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An outbreak of streptococcal pneumonia in a nursin ghome is treated with penicillin. Initial isolates are susceptible to penicillin by Kirby-Bauer agar disc diffusion, but isolates tested later in the same month exhibit only intermediate sensitivity to the drug. What is the most likely mechanism by which drug resistance has appeared and why?

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The General Principles section of the USMLE covers these topics:
Biochemistry
Genetics
Microbiology
Pathology
Pharmacology


1. An outbreak of streptococcal pneumonia in a nursin ghome is treated with penicillin. Initial isolates are susceptible to penicillin by Kirby-Bauer agar disc diffusion, but isolates tested later in the same month exhibit only intermediate sensitivity to the drug. What is the most likely mechanism by which drug resistance has appeared and why?





 
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