The cycle of drug development and the evolution of resistance is a costly one, both in terms of mortality and economics. Over one million resistant infections are acquired each year in . hospitals at an estimated financial cost of 4-5 billion dollars (not to mention increased mortality)! And because they are harder to treat than susceptible infections, antibiotic resistant infections cause more days of hospitalization and missed work. Various sources estimate that in the ., we experience 400,000 additional days of diarrhea due to bacterial infections resistant to a single antibiotic alone and more than 8000 additional days of hospitalization due to resistant salmonella strains.
How exactly does antibiotic resistance evolve? How have such small and simple organisms managed to repeatedly outpace our drugs? The process is quite simply evolution by natural selection but bacteria have a few secret weapons that give them an edge. Imagine a population of bacteria infecting a patient in a hospital. The patient is treated with an antibiotic. The drug kills most of the bacteria but there are a few individual bacteria that happen to carry a gene that allows them to survive the onslaught of antibiotic. These survivors reproduce, passing on the gene for resistance to their offspring, and soon the patient is populated by an antibiotic resistant infection one that not only affects the original patient but that can also be passed on to other patients in the hospital.
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Maura Meade-Callahan, . , is a professor of biology at Allegheny College in Meadville, PA. There she teaches biology, microbiology, and antimicrobial agent resistance in bacteria. She earned her . in plant pathology at North Carolina State University. She is actively involved in a graduate research ethics project of the Association for Practical and Professional Ethics and in various aspects of undergraduate microbiology education through the American Society for Microbiology. She serves as a reviewer for several journals, textbooks, and web sites.