A 37-year-old woman with a history of anorectal abscesses complains of pain in the perianal region. Physical examination reveals mild swelling, tenderness, and erythema of the perianal skin. She is prescribed oral ampicillin and asked to return for follow-up. Two days later, the patient presents with a high-grade fever, syncope, and increased swelling. Which of the following would be the most common mechanism of resistance leading to the failure of antibiotic therapy in this patient?
AIntrinsic absence of a target site for the drug
BUse of an altered metabolic pathway
CProduction of beta-lactamase enzyme
DAltered structural target for the drug
EDrug efflux pump
A 75-year-old man presents to his primary care provider with malaise and low-grade fever after he underwent a cystoscopy for recurrent cystitis and pyelonephritis two weeks ago. His past medical history is significant for coronary artery disease and asthma. His current medications include aspirin, metoprolol, atorvastatin, and albuterol inhaler. Temperature is 37.2°C (99.0°F), blood pressure is 110/70 mm Hg, pulse is 92/min and respirations are 14/min. On physical examination, there are painless areas of hemorrhage on his palms and soles. Cardiac auscultation reveals a new pansystolic murmur over the apex. An echocardiogram shows echogenic endocardial vegetation on a leaflet of the mitral valve. Which of the following pathogens is most likely responsible for his condition?
AStaphylococcus aureus
BEnterococcus
CPseudomonas aeruginosa
DStaphylococcus epidermidis
EStreptococcus gallolyticus
A scientist is studying the mechanisms by which bacteria become resistant to antibiotics. She begins by obtaining a culture of vancomycin-resistant Enterococcus faecalis and conducts replicate plating experiments. In these experiments, colonies are inoculated onto a membrane and smeared on 2 separate plates, 1 containing vancomycin and the other with no antibiotics. She finds that all of the bacterial colonies are vancomycin resistant because they grow on both plates. She then maintains the bacteria in liquid culture without vancomycin while she performs her other studies. Fifteen generations of bacteria later, she conducts replicate plating experiments again and finds that 20% of the colonies are now sensitive to vancomycin. Which of the following mechanisms is the most likely explanation for why these colonies have become vancomycin sensitive?
APoint mutation
BGain of function mutation
CViral infection
DPlasmid loss
ELoss of function mutation
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