An alternative approach to teaching microbial diversity was designed to enhance learning of important concepts in microbiology, increase retention of content, improve microbiology-related skill sets, and positively influence student interest in and disposition toward the natural sciences.

As part of a larger biology curriculum, a course in general microbiology can make significant contributions to student understanding of the themes, topics, mechanisms, and skill sets that are important to the study of the life sciences. One of the challenges for instructors in any college course in the natural sciences is to teach in a manner that helps students develop higher-order cognitive skills. This challenge can be particularly daunting in the instruction of microbiology because of the rapid rate of discovery and because the voluminous scientific findings in microbiology may tempt instructors to present the discipline as an ocean of facts. Here, I describe an alternative philosophy and method for delivering topics of microbial diversity. In this approach, microbial diversity is used as an encompassing theme to investigate the enduring understandings that ought to be a part of a general microbiology course. This is a switch from a content-rich, laundry-list approach to one that is more theme-based. I describe pedagogy, provide class schedules that can be used, and report some assessment data. Although there does not appear to be a statistically significant increase in overall student performance from year to year, there is some evidence of improved performance with content-specific understanding.

Most biological diversity resides in the microbial world. The number of species in the kingdoms Bacteria, Fungi, Protista, and Archaea are predicted to be several million (Tiedje, 1994). Moreover, the diversity within bacteriophages, plant viruses, and animal viruses is thought to exceed what is found in any one of the major kingdoms (Srinivasiah et al., 2008). Courses in general microbiology help introduce students to this vast biological diversity found in the microbial world, though a typical course may cover a relatively small subset of microorganisms. Teaching about microbial diversity in an undergraduate general microbiology course poses several important challenges. Among the primary concerns in revamping the microbiology course at Drake University were (1) emphasizing critical-thinking skills over rote memorization, (2) increasing retention of skills and content, (3) sufficiently covering "enduring understanding" in accordance with national standards, (4) keeping pace with the rapid rates of discovery in microbiology and keeping the content current and relevant, (5) increasing opportunities to think about microbiology in a problem-centric manner, and (6) positively influencing students' disposition toward microbiology by keeping the instruction fun and engaging student interest in the classroom.

Retention of content about specific microorganisms can be challenging as students struggle to commit microbial genera, species, and a multitude of characteristics to memory. There is little dispute that foundational knowledge is critical to the instruction of biology. However, one of the goals of biology classes and biology curricula should be to get students beyond rote memorization and have them apply, analyze, and synthesize new knowledge. There has been an ongoing movement in science instruction away from rote memorization and toward foundational understanding. A report produced by an American Society of Microbiology educational task force identified six overarching concepts that students of microbiology should truly understand: Evolution, Structure and Function, Metabolic Pathways, Information Flow, Systems, and Impact of Microorganisms (http://www.asm.org/images/Education/website%20may%202011%20final.pdf). Additionally, this committee included descriptions of scientific-thinking skills and microbiology-lab-specific skills. The alternative approach described here is in agreement and aligned closely with the thinking and conclusions of this committee.

Current research in microbial diversity and ecology is rapidly changing the discipline of microbiology (Haruta et al., 2009). In light of this, some textbooks that are used in introductory microbiology courses do a fairly good job in keeping their content current. They at least mention current techniques used for microbial community analyses, and they make students aware of the tremendous pace of discovery that is uncovering the richness in microbial life. These advancements give instructors the opportunity to teach the science of microbiology as it is currently being done. To keep instruction up-to-date in any area experiencing rapid change, learning materials within textbooks should be supplemented with primary literature. Instructors who are cognizant of these changes should strive to keep the content and teaching updated.

Another important challenge is in how the content of microbial diversity is communicated. One criticism of current textbooks is the encyclopedic manner in which some of their information is conveyed. To be fair, it might be more reasonable to consider these textbooks as combinations of pedagogical tools and reference manuals. Perhaps to accommodate different types of microbiology courses such as medical, industrial, and environmental microbiology, these textbook chapters provide an incredible list of microbial species, and perhaps the intent is not for students to digest these particular chapters in their entirety, but to focus on selected sections. Maintaining students' interest and keeping them engaged with the study of microbiology means avoiding presenting the information as trivia or in an encyclopedic manner. A related challenge in surveying microbial diversity is in the selection of microbial species to emphasize and study in detail. Which microbes should be studied, and why? The choice in a general microbiology course can be more difficult than in specialized courses. Especially if the class serves as a foundation for advanced courses in the discipline, it may have the responsibility of covering a diverse range of microbes. The teaching of microbial diversity should not be a hindrance to promoting critical thinking. Microbial diversity can be used to emphasize and reinforce the teaching of evolution, biological structure and function, metabolic pathways, genetics, systems biology, and the environmental, medical, and industrial impacts of microbes.

Another issue encountered in the teaching of microbiology and microbial diversity is keeping the information and its study meaningful to students. Certainly, keeping the content current, using recent primary literature, and using events and topics from popular media can aid in keeping the course relevant. Another way is to embed the content in other principles and foundations important to and defining of microbiology and microbiology education (Benson, 2001). This alternative approach attempts to weave themes of microbial diversity into the thinking that is important to the study of microbiology. Using an alternative teaching approach, specific microbes were tied to the investigation of features, mechanisms, processes, and important topics in microbiology. The rationale was that presenting the learning materials in this manner would enhance understanding of themes in microbiology and the recall of microbiology-related content. Yet another way is to teach microbial diversity in a problem-centric manner, seeking to understand, solve, or advance knowledge about a microbiology-related problem (Benson, 2001). These ideas were further emphasized in the laboratory, and the students were given opportunities to work with a very diverse collection of microbes, in the context of laboratory controls or laboratory unknowns. Students worked in a problem-centric manner in the identification of sets of unknowns. They were given the responsibility of designing classification schemes and picking good experimental controls. They were permitted the freedom to design their own lines of inquiry.

This approach was not intended to be a substitute for classroom pedagogies that have been demonstrated to be effective in the instruction of microbiology, such as active learning, collaborative learning, and inquiry-based and problem-based learning (Seifert et al., 2009; Southwick et al., 2010). This approach nicely complemented what was already being done in the microbiology classroom at Drake University, utilizing microbial diversity as a unifying theme in an attempt to increase student interest, enhance learning, and increase retention of course content.

Microbiology Lecture

The theme of diversity in the microbial world was introduced during the first day of class and extended throughout the semester. The students discussed human immunodeficiency virus (HIV) and Plasmodium malariae on that first day. These were two microbes with which virtually all students had some familiarity. Using HIV and P. malariae as examples, the relevance of microbiology to global public health was discussed. In using this approach, one concern at the beginning of the semester was that students would be lacking in foundational knowledge needed to have meaningful discussions about microbiology, microbial life forms, and viruses. This was not observed to be the case, and students were very engaged in talking about the numbers of people globally affected by HIV and malaria and the parts of the world where malaria is endemic. The discussion on this first day really seemed to capture student interest in microbiology, likely because the major theme was the impact that microbes can have on the health of human populations.

Specific microbes were highlighted during each classroom session, and the choice of these microbes had some relationship with the topic being studied. In most cases the associations were fairly obvious and the selection of which microbes to discuss seemed natural. In discussing bacterial endospores as unique microbial structures, the example of Clostridium botulinum was used. Emphasizing this species also helped feed a lecture and discussions about food poisoning, neurotoxins, botox, and the durability of bacterial endospores. In discussing antibiotics, Penicillium chrysogenum was highlighted. The class watched a short video clip about Alexander Fleming and the discovery of penicillin. Talking about penicillin and the fungal species originally used to isolate the small molecule supported dialogue about discovery in microbiology and chemotherapeutics and about natural products that can be isolated from microbes. The students worked in pairs to list advantages that could be conferred by modification of naturally occurring antibiotics. We talked about how antibiotics are discovered and characterized and how this information is germane to the development of semisynthetic antibiotics. There were opportunities to review and emphasize responsible antibiotic use and why and how these measures should be employed. A sample lecture outline is provided in Figure 1.

Figure 1.

A sample lecture outline on the topic of water purification. Importantly, the lecture was supplemented by student problem solving, collaborative learning, and discussion.

Figure 1.

A sample lecture outline on the topic of water purification. Importantly, the lecture was supplemented by student problem solving, collaborative learning, and discussion.

In other cases the associations were not completely obvious. In lecturing about differing types of microscopy, Treponema pallidum was highlighted because these spirochetes have been distinguished using dark-field microscopy, being very difficult to stain and to visualize using bright-field microscopy. This fueled an activity in which each student worked with a partner to describe the advantages and disadvantages of the differing types of microscopy covered. In another class, Chlamydia trachomatis was highlighted when discussing clinical microbiology, and the focus on this microbe enabled discussion about how clinical specimens are collected and how polymerase-chain-reaction techniques can be used to diagnose certain infections.

Assigned readings in the textbook and in primary literature helped to encourage discussion. In many cases, questions were used to prompt student responses. The students were given time to formulate answers and, often, to consult with a partner in class. There was extra attention invested in keeping the classroom environment safe and academic so that the students felt free to ask questions and free to interrupt lecture or discussion if particular points needed clarification or stimulated additional questions.

In general, the class focused on one or two microbes during each lecture. The content covered, principal ideas, and the microbes used to highlight these topics are shown in Table 1. The diversity studied throughout the lectures and labs were brought together at the end of the semester in a discussion about microbial evolution and microbial phylogenetics. In discussing evolution and phylogenetics, important considerations in modern microbiology were addressed (Woese, 1994; Pace, 2008) and the class reevaluated the terms "prokaryotic" and "eukaryotic," revisited the position of Domain Archaea and Kingdom Archaea in the tree of life, and reexamined the role microbial genetics has had in restructuring our understanding of evolutionary relatedness.

Table 1.

Using microbial diversity as a unifying theme in a general microbiology class.

TopicKey ConceptsMicrobe
Introduction to Microbiology Overview on the Importance of Microbial Life Plasmodium malariae
HIV 
Principles of Microscopy Magnification, Resolution Treponema pallidum
Poxviruses 
Specimen Preparation and Staining Fixation, Simple Stains,
Differential Staining, Gram Staining 
Klebsiella pneumoniae
Mycobacterium tuberculosis 
Prokaryotic and Eukaryotic Life Taxonomic Domains, Kingdoms Giardia lamblia
Schistosoma 
Microbial Physiology Cell Structure and Morphology

Cell Walls, Outer Membranes, 
Bacillus subtilis
Micrococcus luteus
Clostridium botulinum 
Chemistry of Cellular Components Fimbriae, Capsules, Endospores Neisseria gonorrhea 
Microbial Motility Bacterial Motility Proteus vulgaris 
Microbial Nutrition and Culture Culture Media, Aseptic Techniques Haemophilus influenzae 
Microbial Metabolism Fermentation, Microbial Biochemistry Saccharomyces cerevisiae 
Bacterial Genetics Ames Test, Mutagenesis Salmonella enterica 
Microbial Genomics Bioinformatics, Transcriptomes  
Microbial Gene Regulation Prokaryotic Gene Regulation, Operons
Eukaryotic Gene Regulation, Transcription Factors 
Escherichia coli 
Measuring Microbial Growth Growth Cycles, Growth Conditions Thermophilus aquaticus 
Factors Influencing Microbial Growth Cardinal Temperatures, Oxygen Requirements Bacteroides fragilis 
Control of Microbial Growth Sterilization, Microbiostatics, Microbicidals Listeria monocytogenes
Campylobacter jejuni 
Pathogenicity Virulence, Toxins Candida albicans 
Normal Microbiota Opportunistic Pathogens, Probiotics Bifidobacterium animalis 
Microbial Diagnostics Serology, ELISAs Streptococcus pneumoniae 
Clinical Microbiology Specimens and Cultures
Nosocomial Infections 
Chlamydia trachomatis
Staphylococcus aureus 
Chemotherapeutics Antibiotics, Antifungals, Antivirals Penicillium chrysogenum 
Microbial Ecology Nutrient and Chemical Cycles Rhizobium leguminisarium 
Environmental Microbiology Soil Microbiology  
Water Purification Waterborne Infectious Agents
Coliforms 
Vibrio cholerae
Enterobacter aerogenes 
Wastewater Treatment Biochemical Oxygen Demand Burkholderia cepacia 
Bioremediation Xenobiotics Pseudomonas aeruginosa 
Epidemiology Mortality, Morbidity Influenza virus 
Public Health  Rhinovirus 
Emerging Infectious Diseases Epidemics, Microbial Surveillance Yersinia pestis 
Innate Immunity Inflammation, Toll-like Receptors, PAMPs
Leukocytes 
Streptococcus pyogenes 
Adaptive Immunity Antigens, Antibodies, Lymphocytes
Immunizations 
Herpes simplex virus
Poliovirus 
Industrial Microbiology Bioreactors, Enzyme Purification Lactobacillus acidophilus 
Food Microbiology Spoilage, Pasteurization Aspergillus 
Biofuels Ethanol Production, Biodiesel, Helioculture Botryococcus braunii 
Biotechnology Transgenic Organisms
Bioethics 
Agrobacterium tumefaciens
Bacillus thuringiensis 
Microbial Evolution Origins of Life Crenarchaeota 
Microbial Phylogenetics Tree of Life, Revisiting Prokaryotes/Eukaryotes Euryarchaeota 
TopicKey ConceptsMicrobe
Introduction to Microbiology Overview on the Importance of Microbial Life Plasmodium malariae
HIV 
Principles of Microscopy Magnification, Resolution Treponema pallidum
Poxviruses 
Specimen Preparation and Staining Fixation, Simple Stains,
Differential Staining, Gram Staining 
Klebsiella pneumoniae
Mycobacterium tuberculosis 
Prokaryotic and Eukaryotic Life Taxonomic Domains, Kingdoms Giardia lamblia
Schistosoma 
Microbial Physiology Cell Structure and Morphology

Cell Walls, Outer Membranes, 
Bacillus subtilis
Micrococcus luteus
Clostridium botulinum 
Chemistry of Cellular Components Fimbriae, Capsules, Endospores Neisseria gonorrhea 
Microbial Motility Bacterial Motility Proteus vulgaris 
Microbial Nutrition and Culture Culture Media, Aseptic Techniques Haemophilus influenzae 
Microbial Metabolism Fermentation, Microbial Biochemistry Saccharomyces cerevisiae 
Bacterial Genetics Ames Test, Mutagenesis Salmonella enterica 
Microbial Genomics Bioinformatics, Transcriptomes  
Microbial Gene Regulation Prokaryotic Gene Regulation, Operons
Eukaryotic Gene Regulation, Transcription Factors 
Escherichia coli 
Measuring Microbial Growth Growth Cycles, Growth Conditions Thermophilus aquaticus 
Factors Influencing Microbial Growth Cardinal Temperatures, Oxygen Requirements Bacteroides fragilis 
Control of Microbial Growth Sterilization, Microbiostatics, Microbicidals Listeria monocytogenes
Campylobacter jejuni 
Pathogenicity Virulence, Toxins Candida albicans 
Normal Microbiota Opportunistic Pathogens, Probiotics Bifidobacterium animalis 
Microbial Diagnostics Serology, ELISAs Streptococcus pneumoniae 
Clinical Microbiology Specimens and Cultures
Nosocomial Infections 
Chlamydia trachomatis
Staphylococcus aureus 
Chemotherapeutics Antibiotics, Antifungals, Antivirals Penicillium chrysogenum 
Microbial Ecology Nutrient and Chemical Cycles Rhizobium leguminisarium 
Environmental Microbiology Soil Microbiology  
Water Purification Waterborne Infectious Agents
Coliforms 
Vibrio cholerae
Enterobacter aerogenes 
Wastewater Treatment Biochemical Oxygen Demand Burkholderia cepacia 
Bioremediation Xenobiotics Pseudomonas aeruginosa 
Epidemiology Mortality, Morbidity Influenza virus 
Public Health  Rhinovirus 
Emerging Infectious Diseases Epidemics, Microbial Surveillance Yersinia pestis 
Innate Immunity Inflammation, Toll-like Receptors, PAMPs
Leukocytes 
Streptococcus pyogenes 
Adaptive Immunity Antigens, Antibodies, Lymphocytes
Immunizations 
Herpes simplex virus
Poliovirus 
Industrial Microbiology Bioreactors, Enzyme Purification Lactobacillus acidophilus 
Food Microbiology Spoilage, Pasteurization Aspergillus 
Biofuels Ethanol Production, Biodiesel, Helioculture Botryococcus braunii 
Biotechnology Transgenic Organisms
Bioethics 
Agrobacterium tumefaciens
Bacillus thuringiensis 
Microbial Evolution Origins of Life Crenarchaeota 
Microbial Phylogenetics Tree of Life, Revisiting Prokaryotes/Eukaryotes Euryarchaeota 

The approach that the microbiology course had taken prior to the reforms was to cover first the foundational knowledge in microbiology and then apply these principles and descriptors such as Gram +/-, oxygen requirements, ability to utilize specific carbohydrate energy sources, et cetera to differing species of bacteria in an encompassing microbial-diversity unit. Using examples of microbes to reinforce foundational ideas did not appear to hamper classroom discussions. A collection of more than 40 different bacteria, fungi, animal parasites, archaea, and viruses were covered over the course of the semester.

Microbiology Laboratory

The microbiology laboratory emphasized inquiry-based experimentation that centered around identification of microbial unknowns. The students identified or characterized multiple sets of unknowns, including (1) unknowns gathered from the microbiota of their hands as part of a handwashing experiment, (2) a laboratory unknown from a library of 30 microbes, (3) upper- respiratory-tract microbes cultured from throat swabs, (4) microbes cultured from mouth swabs, and (5) environmental unknowns cultured from water samples.

At Drake University, the general microbiology laboratory course meets twice a week and each lab session lasts 2 hours. The first quarter of the semester is spent learning basic lab techniques. Concurrent with these basic exercises and along with known microbial controls, the students subculture, stain, and test biochemical properties of unknown samples. Over the 16-week class, the students have opportunities to work with a wide range of microbes in their experiments (Table 2 and Figure 2). Working with the unknowns, attempting to identify them, utilizing a diverse range of microbial controls, and producing lab reports from their experimental results gave the students additional working experience with multiple culturable species. The laboratory was designed to intentionally have the students use many differing microbial species. In the handling of these microbial species, good laboratory practices were emphasized and the students were instructed to treat every specimen, even if it was a known control, as a potential pathogen. That being said, in assigning laboratory unknowns, the use of potential pathogens was mostly avoided. In Table 2, the Notes column draws attention to pathogenic species. Each student cultured, stained, observed, researched the literature, discussed with their lab partners, and reported on 18 to 24 species by the end of the semester.

Table 2.

How a diverse array of microbes can be incorporated into a microbiology lab.

MicrobeMediaNotes
Acinetobacter calcoaceticus Brain heart infusion agar Pathogenic, Gram (-) bacilli 
Alcaligenes faecalis Nutrient agar Pathogenic, Gram (-) coccobacilli 
Bacillus laterosporus Nutrient agar Gram (+) bacilli, endospore-forming 
Bacillus megaterium Nutrient agar Gram (+) bacilli, endospore-forming 
Bacillus stearothermophilus Nutrient agar Gram (+) bacilli, endospore-forming, culture at 55°C 
Bacillus subtilis Nutrient agar Gram (+) bacilli, endospore-forming 
Citrobacter freundii Nutrient agar Gram (-) bacilli 
Clostridium perfringens Brewer's anaerobic agar Pathogenic, Gram (+) bacilli, obligate anaerobe 
Clostridium sporogenes Brewer's anaerobic agar Gram (+) bacilli, obligate anaerobe 
Corynebacterium xerosis Brain heart infusion agar Gram (+) bacilli, palisade arrangement 
Enterobacter aerogenes Nutrient agar Gram (-) bacilli 
Escherichia coli Nutrient agar Gram (-) coccobacilli 
Klebsiella pneumoniae Nutrient agar Pathogenic, Gram (-) bacilli 
Lactobacillus acidophilus MRS agar Gram (+) bacilli 
Micrococcus luteus Nutrient agar Gram (+) cocci, tetrads, yellow colonies 
Mycobacterium phlei Brain heart infusion agar Pathogenic, acid-fast 
Mycobacterium smegmatis Brain heart infusion agar Pathogenic, acid-fast 
Penicillium chrysogenum Sabouraud agar Fungus 
Proteus vulgaris Nutrient agar Pathogenic, Gram (-) bacilli 
Pseudomonas aeruginosa Nutrient agar Pathogenic, Gram (-) bacilli 
Pseudomonas fluorescens Nutrient agar Gram (-) bacilli 
Rhodospirillum rubrum Nutrient agar Gram (-), spiral-shaped, photosynthetic, needs light 
Saccharomyces cerevisiae Sabouraud agar Fungus 
Salmonella typhimurium Nutrient agar Pathogenic, Gram (-) bacilli 
Serratia marcescens Nutrient agar Gram (-) bacilli, colonies are white at 37°C, red at 25°C 
Shigella flexneri Nutrient agar Pathogenic, Gram (-) bacilli 
Staphylococcus aureus Nutrient agar Pathogenic, Gram (+) cocci, clustered 
Staphylococcus epidermidis Nutrient agar Gram (+) cocci, clustered 
Streptococcus pyogenes Blood agar Pathogenic, Gram (+) cocci, chains, beta-hemolytic 
Streptomyces griseus Yeast malt extract agar Gram (+), form hyphae 
Vibrio anguillarum Marine agar Gram (-), vibrioid 
Vibrio fischeri Marine agar Gram (-), vibrioid, fluorescent 
MicrobeMediaNotes
Acinetobacter calcoaceticus Brain heart infusion agar Pathogenic, Gram (-) bacilli 
Alcaligenes faecalis Nutrient agar Pathogenic, Gram (-) coccobacilli 
Bacillus laterosporus Nutrient agar Gram (+) bacilli, endospore-forming 
Bacillus megaterium Nutrient agar Gram (+) bacilli, endospore-forming 
Bacillus stearothermophilus Nutrient agar Gram (+) bacilli, endospore-forming, culture at 55°C 
Bacillus subtilis Nutrient agar Gram (+) bacilli, endospore-forming 
Citrobacter freundii Nutrient agar Gram (-) bacilli 
Clostridium perfringens Brewer's anaerobic agar Pathogenic, Gram (+) bacilli, obligate anaerobe 
Clostridium sporogenes Brewer's anaerobic agar Gram (+) bacilli, obligate anaerobe 
Corynebacterium xerosis Brain heart infusion agar Gram (+) bacilli, palisade arrangement 
Enterobacter aerogenes Nutrient agar Gram (-) bacilli 
Escherichia coli Nutrient agar Gram (-) coccobacilli 
Klebsiella pneumoniae Nutrient agar Pathogenic, Gram (-) bacilli 
Lactobacillus acidophilus MRS agar Gram (+) bacilli 
Micrococcus luteus Nutrient agar Gram (+) cocci, tetrads, yellow colonies 
Mycobacterium phlei Brain heart infusion agar Pathogenic, acid-fast 
Mycobacterium smegmatis Brain heart infusion agar Pathogenic, acid-fast 
Penicillium chrysogenum Sabouraud agar Fungus 
Proteus vulgaris Nutrient agar Pathogenic, Gram (-) bacilli 
Pseudomonas aeruginosa Nutrient agar Pathogenic, Gram (-) bacilli 
Pseudomonas fluorescens Nutrient agar Gram (-) bacilli 
Rhodospirillum rubrum Nutrient agar Gram (-), spiral-shaped, photosynthetic, needs light 
Saccharomyces cerevisiae Sabouraud agar Fungus 
Salmonella typhimurium Nutrient agar Pathogenic, Gram (-) bacilli 
Serratia marcescens Nutrient agar Gram (-) bacilli, colonies are white at 37°C, red at 25°C 
Shigella flexneri Nutrient agar Pathogenic, Gram (-) bacilli 
Staphylococcus aureus Nutrient agar Pathogenic, Gram (+) cocci, clustered 
Staphylococcus epidermidis Nutrient agar Gram (+) cocci, clustered 
Streptococcus pyogenes Blood agar Pathogenic, Gram (+) cocci, chains, beta-hemolytic 
Streptomyces griseus Yeast malt extract agar Gram (+), form hyphae 
Vibrio anguillarum Marine agar Gram (-), vibrioid 
Vibrio fischeri Marine agar Gram (-), vibrioid, fluorescent 
Figure 2.

Micrographs produced by students in the microbiology laboratory. Lab exercises and student-designed inquiry-based experiments were an important component of the microbiology course and the alternative approach to microbiology instruction. In this figure are two examples of a Gram stain that students performed on microbes they isolated from the environment.

Figure 2.

Micrographs produced by students in the microbiology laboratory. Lab exercises and student-designed inquiry-based experiments were an important component of the microbiology course and the alternative approach to microbiology instruction. In this figure are two examples of a Gram stain that students performed on microbes they isolated from the environment.

Assessment

The assessments reported here consist of course evaluations and the results of student exams in aggregate. In 2008, the bulk of microbial diversity was covered in a single unit, an approach that had traditionally been used at Drake University. Thus, the spring semester of 2008 served as a baseline and "control" comparison for subsequent semesters. The alternative approach of teaching microbial diversity to enhance understanding of themes in microbiology was implemented in the spring of 2009. Use of this alternative pedagogical tool was continued in 2010 and 2011. Assessment data attempting to evaluate the effectiveness of this approach were gathered during each of these 3 years.

Understanding of Key Concepts

How did the students perform overall in the microbiology class? The aggregate data from class exams showed no statistically significant difference between the traditional approach and the alternative approach. There was no significant difference in overall student performance between the control year and the years that the alternative approach was used. The data show a small increase in mean scores when the alternative approach was used, but the significance of this difference when analyzed with a two-tailed t-test gave P values >0.11 (Figure 3). During the control year, the average exam score was 79.7, whereas in the spring semester of 2009, 2010, and 2011, average exam scores were 81.7, 81.4, and 83.3, respectively.

The exams were structured as timed 50-question tests that were a mix of multiple choice and short answer, with some variations on these types of questions. Many questions attempted to assess student understanding and comprehension and their ability to interpret and extrapolate correct answers. The ability to analyze and apply knowledge, as defined by Bloom's taxonomy, was also a major part of the assessment. There were few questions that tested basic recall, and there were some, but also relatively few, that attempted to assess higher-order synthesis and evaluation thinking skills.

However, as a result of the alternative approach, there were improvements observed in student performance with exam questions related to microbial diversity. In the control year, the bulk of microbial diversity was tested on a single unit exam. Forty-five students took this exam, and the average of all scores was 81.3% with a standard deviation of 10.1% (Figure 4).

Figure 3.

The alternative approach to teaching and learning microbial diversity had little impact on overall performance in general microbiology. Students learning about microbial diversity using the traditional (2008, n = 45) versus the alternative method (2009, n = 46; 2010, n = 40; 2011, n = 41) showed no statistically significant improvement in their performance on written exams. To determine the significance of the differences between the traditional and alternative approaches, a two-tailed t-test was used. The P values ranged from <0.29 to <0.57. Written exams were structured as multiple-choice questions and short-answer questions, with some variations on these two basic types of questions.

Figure 3.

The alternative approach to teaching and learning microbial diversity had little impact on overall performance in general microbiology. Students learning about microbial diversity using the traditional (2008, n = 45) versus the alternative method (2009, n = 46; 2010, n = 40; 2011, n = 41) showed no statistically significant improvement in their performance on written exams. To determine the significance of the differences between the traditional and alternative approaches, a two-tailed t-test was used. The P values ranged from <0.29 to <0.57. Written exams were structured as multiple-choice questions and short-answer questions, with some variations on these two basic types of questions.

Figure 4.

The alternative approach to teaching and learning microbial diversity improved student recall and understanding of microbial diversity themes. Students learning about microbial diversity using the traditional (2008, n = 45) versus the alternative method (2009, n = 46; 2010, n = 40; 2011, n = 41) showed a significant improvement in their performance on written exam questions pertaining to themes in microbial diversity. A two-tailed t-test was employed for statistical comparison. Statistically significant differences with P values <0.03 were observed for all 3 years in which the alternative pedagogy was employed in comparison to the control year.

Figure 4.

The alternative approach to teaching and learning microbial diversity improved student recall and understanding of microbial diversity themes. Students learning about microbial diversity using the traditional (2008, n = 45) versus the alternative method (2009, n = 46; 2010, n = 40; 2011, n = 41) showed a significant improvement in their performance on written exam questions pertaining to themes in microbial diversity. A two-tailed t-test was employed for statistical comparison. Statistically significant differences with P values <0.03 were observed for all 3 years in which the alternative pedagogy was employed in comparison to the control year.

In the first year in which the alternative approach was implemented, the assessment of student learning on topics of microbial diversity was similar to that used in 2008. The students were asked to recall information, make inferences, analyze data, tables, and graphs, and apply understanding of specific microbial species. There were five regularly scheduled exams, each of which had some component that assessed student knowledge of microbial diversity, and the final comprehensive exam was focused on topics surrounding microbial diversity. The average score on this final exam was 83.2% (n = 46), with a standard deviation of 10.3%. In the following years, the same strategy was used for the final comprehensive exam. The students performed quite well on these tests. In the second experimental year, the average score was 87.1% (n = 40), with a standard deviation of 8.0%. In the third experimental year, the students scored an average of 86.8% (n = 41) and the standard deviation for this test was 3.9%. Comparison of exam scores between the control year and the experimental years revealed statistically significant trends. Using a two-tailed t-test, P values were <0.03 (Table 2) for the three comparisons that were made.

There are important caveats in the interpretation of these observations. Student assessment was not identical over the course of the study, and there were changes that were introduced each semester. Many exam questions, though similar from year to year, were changed and refined in progressive semesters. An example of a question that students performed very well with during the control year was this (correct answer in bold):

Which of the following is an obligate intracellular parasite of humans?

  1. A. Salmonella enterica

  2. B. Vibrio cholera

  3. C. Influenza B virus

  4. D. Klebsiella pneumoniae

  5. E. Yersinia pestis

The question changed slightly the following year to read:

In which of the following ways are influenza virus and Chlamydia trachomatis similar?

  1. A. Both belong to the domain Bacteria

  2. B. Both are obligate intracellular pathogens

  3. C. Both are Gram (+)

  4. D. Both are Gram (-)

  5. E. Both are lacking a membrane

Interestingly, there was virtually no difference in student performance with the modified question. An example of a basic recall question that (surprisingly) many students struggled with during the control year was:

Which of the following is considered to be a genus of enteric bacteria?

  1. A. Neisseria

  2. B. Vibrio

  3. C. Bordetella

  4. D. Salmonella

  5. E. Streptococcus

This question about Salmonella was altered so that it did not solely assess basic recall, but attempted to assess understanding in addition to recall:

There are over 2000 differing serovars of Salmonella. Which of the listed reagents would be most useful in differentiating between the serovars?

  1. A. DNA dyes

  2. B. Cell surface antibodies

  3. C. Fermentation tests

  4. D. Gram staining reagents

  5. E. Flagellar stains

Short-answer questions provided greater flexibility in helping to assess the extent of student understanding. Examples of short- answer questions used on these assessments included:

  • Explain why postmenopausal women are at increased risk of yeast infections.

  • Explain the mechanism by which sucrose contributes to dental caries.

  • Explain why tetracycline can be used to inhibit growth of Yersinia pestis but is ineffective at controlling Candida albicans.

These questions provide perhaps a broader assessment of student understanding (or misunderstanding).

Student Impressions & Disposition

The alternative methodology was largely developed in response to criticisms with how particular sections of the microbiology unit had been taught. This was despite the fact that the students performed relatively well on their unit exam (average score 81.3%). Examples of student remarks included: "Please include less information in the microbial diversity section"; "I would enjoy more learning of actual bacteria in depth"; and "Spend more time learning about the different bacteria and their characteristics."

The narrative evidence provided by the students during the first year the new approach was implemented was overwhelmingly positive. The students remarked on course evaluations, "The individual microorganism close-ups were very beneficial and interesting in that it gave us clear examples of different microorganisms and how they affect us"; "I feel that I learned a lot about microbiology and it's information that I will remember"; and "I feel like I've learned a lot about microbiology and was actually interested in the material." This alternative approach continued to garner positive comments and appeared to have positively influenced student disposition about microbiology. In general, the students were appreciative that the material was not conveyed as an onerous and long laundry-list of facts.

In their course evaluations, the students were given opportunities to rate their level of satisfaction or dissatisfaction with the course. They were asked to numerically score on a scale of 1-5 (or A-E) important aspects of the class (Table 3). The lecture and laboratory components of the course were evaluated in a similar manner and were scored separately. A score of 1 was a poor rating, and a rating of 5 was excellent. During the control year, the students rated the quality of the discussions and lectures with an average score of 4.2, with 40% of the class rating the discussions and lectures as excellent. Satisfaction with the course format and class objectives was marked with an average score of 4.6. Approximately 64% of students rated the traditional format and class objectives as being excellent.

Table 3.

Student perceptions of conventional and alternative approaches to microbiology instruction.

Excellent (5 or A)Very Good (4 or B)Average (3 or C)Below Average (2 or D)Poor (3 or E)Average Numeric Score (1-5)
2008 
1. Overall quality of lectures and discussions 40% 40% 20% 0% 0% 4.2 
2. Quality of course format and objectives 69% 27% 4% 0% 0% 4.6 
3. Emphasis on critical thinking 33% 38% 27% 2% 0% 4.0 
2009 
1. Overall quality of lectures and discussions 71% 29% 0% 0% 0% 4.4 
2. Quality of course format and objectives 67% 31% 2% 0% 0% 4.3 
3. Emphasis on critical thinking 60% 29% 12% 0% 0% 4.2 
2010 
1. Overall quality of lectures and discussions 64% 36% 0% 0% 0% 4.6 
2. Quality of course format and objectives 70% 30% 0% 0% 0% 4.7 
3. Emphasis on critical thinking 67% 30% 3% 0% 0% 4.6 
2011 
1. Overall quality of lectures and discussions 54% 46% 0% 0% 0% 4.5 
2. Quality of course format and objectives 59% 41% 0% 0% 0% 4.6 
3. Emphasis on critical thinking 69% 28% 3% 0% 0% 4.7 
Excellent (5 or A)Very Good (4 or B)Average (3 or C)Below Average (2 or D)Poor (3 or E)Average Numeric Score (1-5)
2008 
1. Overall quality of lectures and discussions 40% 40% 20% 0% 0% 4.2 
2. Quality of course format and objectives 69% 27% 4% 0% 0% 4.6 
3. Emphasis on critical thinking 33% 38% 27% 2% 0% 4.0 
2009 
1. Overall quality of lectures and discussions 71% 29% 0% 0% 0% 4.4 
2. Quality of course format and objectives 67% 31% 2% 0% 0% 4.3 
3. Emphasis on critical thinking 60% 29% 12% 0% 0% 4.2 
2010 
1. Overall quality of lectures and discussions 64% 36% 0% 0% 0% 4.6 
2. Quality of course format and objectives 70% 30% 0% 0% 0% 4.7 
3. Emphasis on critical thinking 67% 30% 3% 0% 0% 4.6 
2011 
1. Overall quality of lectures and discussions 54% 46% 0% 0% 0% 4.5 
2. Quality of course format and objectives 59% 41% 0% 0% 0% 4.6 
3. Emphasis on critical thinking 69% 28% 3% 0% 0% 4.7 

The students in the first year of the alternative teaching style rated the discussions and lectures with an average score of 4.7, with 70% of students rating them excellent. Course format and class objectives received an average rating of 4.7, with 66% marking the format and objectives as excellent. These positive sentiments about the course were echoed in the second and third experimental years, and 64% and 51%, respectively, of these classes rated the discussions and lectures of this alternative approach to teaching microbiology as excellent.

Using microbial diversity as the theme tying together the content in microbiology did not appear to hinder the emphasis on critical-thinking skills, judging from student perceptions. The students perceived that there was more of an emphasis on critical thinking using the alternative approach compared with the control year. With each year of this study, a greater percentage of students felt that critical-thinking skills were being taught.

Content Retention

Assessment of longer-term retention was desirable, but its collection was complicated by several factors. The major problem was that the opportunities to assess content retention were limited. One opportunity that had been taken was to assess students enrolled in a higher-level immunology course. Certainly, this method suffers from selection bias, given that students who were unsuccessful in microbiology were highly unlikely to continue on to take the immunology class. Successful completion of a course in microbiology is listed as a prerequisite for this class. However, special waivers of this prerequisite may be granted if the student completed other courses in biology and performed sufficiently well in them.

A precourse assessment was used to identify a cohort of students that had completed microbiology when the alternative approach was utilized. Data from two precourse assessments were collected. Following the conclusion of the first experimental semester, the students were assessed for longer-term retention of content from the microbiology course. This was approximately 3 months after the conclusion of the 2009 microbiology class. Multiple-choice and short-answer pretests were used to address student recall of information pertaining to topics in microbial diversity. Disappointingly, the students enrolled in microbiology when the alternative approach was first instituted (n = 11) achieved an average score of 38%. The students who completed microbiology in classes that did not utilize this approach (n = 6) scored an average of 27%. A two-tailed student's t-test performed on the assessment data yielded a P value <0.10.

In the following year, the precourse assessment for immunology was altered and included 13 newly designed multiple-choice questions. The purpose of the redesign was to better evaluate theme-based understanding of concepts in microbiology. The new questions tested higher-order understanding. Students who successfully completed the microbiology course and who received instruction with this alternative approach (n = 13) achieved an average score of 8.4 out of 13 (65%), with a standard deviation of 2.2 (17%). Unfortunately, there were insufficient data available from immunology students who had taken the microbiology course during the control year. The low number of students belonging to this group made comparisons not meaningful. However, present in this class was a small cohort (n = 4) that had not taken a prior microbiology course. This group achieved an average score of 4.8 (37%), with a standard deviation of 0.5 (3.8%). The difference between students who had not taken microbiology and those who were instructed using the alternative approach was significant (P < 0.0001).

Discussion

This study describes an alternative method for teaching content concerning microbial diversity. A problem that had been encountered was that students were retaining disappointingly little information about microbiology, and their evaluations expressed dissatisfaction with how it was being taught. The intent of these reforms was to increase student interest and engagement with the content of microbial diversity. The hope was that if these goals were realized, retention and recall of information, microbiology-related skills, and overall performance in the class would also improve. This alternative approach had its genesis in attempting to meet the challenges students face in digesting the large quantity of knowledge in microbial diversity, keep pace with the tremendous amount of information being generated, emphasizing critical thinking, and increase student interest in microbiology. Certainly, prevailing teaching attitudes de-emphasize rote memorization in favor of higher-level analytical skills. However, there are certain facts that we need for students to know in order to make the class teachable. Moreover, instructors have expectations for a certain body of knowledge that students must possess to successfully complete a course. For example, microbiology students should know and remember that E. coli is a Gram (-) bacterium, they should know what a coliform is, and they should be able to give an example of a coliform. This information should be retained, and it should be used to construct more important stories that incorporate complex themes of biology.

The alternative approach to teaching the microbiology laboratory encouraged the use of as many different species as practically feasible. Doing this gave the students hands-on practical experience in culturing, observing, and communicating about many types of experience. The diversity that was emphasized in lecture was also emphasized in the laboratory, and lab experiments were designed to get the students to work in a problem-centered manner.

When they were surveyed, their dispositions as assessed by written and anonymous evaluations appeared to be more positive when the alternative approach was instituted. Narrative evidence provided in student comments was overwhelmingly positive for the alternative approach to teaching and using microbial diversity. These changes did not appear to significantly influence the students' perceptions of course format, class objectives, or fairness of the assessment. The students rated the quality of lectures and discussions higher when this alternative pedagogy was utilized.

Student performance, as measured with written examinations over the course of this study, were done with differing populations, during differing semesters, and where there were likely, from a student's perspective, significant differences in the assessment and teaching. Unfortunately, the data suggest that anticipated gains in overall student performance were not achieved. Statistical analyses suggest that there were no marked improvements in overall performance in the class. The data suggest that the alternative approach did not hamper instruction in other content areas and did not result in an overall decrease in student performance. These analyses did reveal gains made in content-specific themes. Using this approach, students performed better at properly answering questions related to topics of microbial diversity. A full analysis measuring student performance based on the type of question as categorized by Bloom's taxonomy was not done. The alternative pedagogy was an intentional attempt to increase student learning in all areas and overall performance in a microbiology course. In future assessments it may be worthwhile to determine whether and how different skills within the cognitive domain are influenced.

In conclusion, this study describes an alternative approach that microbiology instructors can utilize to incorporate microbial diversity as a central theme in an introductory-level course in general microbiology and microbiology lab. The students reacted positively to the changes. Although there were no significant improvements in overall performance in the class as measured by aggregate exam data, the students appeared to make gains in recalling and understanding themes specifically related to the characteristics of individual microbes. It is tempting to make extrapolations to other areas of biology instruction in which students are asked to learn materials that might appear to them as a long laundry-list of knowledge. Pedagogies that take laundry-list items and study some of them in greater detail and weave some of those items into greater themes of the class may increase students' satisfaction with their studies and may make the knowledge more meaningful to them.

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