Tuberculosis (TB) continues to be a serious global health problem, resulting in >1.4 million deaths each year. Of increasing concern is the evolution of antibiotic-resistant strains of the bacterium that causes TB. Using this real-world scenario, we created a 90-minute activity for high school or undergraduate students to use online bioinformatics tools to detect single-nucleotide polymorphisms (SNPs) between a wild-type and a variant Mycobacterium tuberculosis gene that could confer resistance to a commonly used TB antibiotic, rifampin. Students write a scientific explanation, providing evidence and reasoning, to support their claim of antibiotic resistance or susceptibility. The entire lesson can be found online at http://www.stronglab.org/taylor .