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 42-year-old woman with a history of multiple sclerosis and recurrent urinary tract infections comes to the emergency department because of flank pain and fever. Her temperature is 38.8°C (101.8°F). Examination shows left-sided costovertebral angle tenderness. She is admitted to the hospital and started on intravenous vancomycin. Three days later, her symptoms have not improved. Urine culture shows growth of Enterococcus faecalis. Which of the following best describes the most likely mechanism of antibiotic resistance in this patient?
AIncreased efflux across bacterial cell membranes
BProduction of beta-lactamase
CAlteration of penicillin-binding proteins
DAlteration of peptidoglycan synthesis
EAlteration of ribosomal targets
A team of intensivists working in a private intensive care unit (ICU) observe that the clinical efficacy of vancomycin is low, and proven nosocomial infections have increased progressively over the past year. A clinical microbiologist is invited to conduct a bacteriological audit of the ICU. He analyzes the microbiological reports of all patients treated with vancomycin over the last 2 years and takes relevant samples from the ICU for culture and antibiotic sensitivity analysis. The audit concludes that there is an increased incidence of vancomycin-resistant Enterococcus fecalis infections. Which of the following mechanisms best explains the changes that took place in the bacteria?
ADecreased number of porins in the bacterial cell wall leading to decreased intracellular entry of the antibiotic
BProduction of an enzyme that hydrolyzes the antibiotic
CProtection of the antibiotic-binding site by Qnr protein
DIncreased expression of efflux pumps which extrude the antibiotic from the bacterial cell
EReplacement of the terminal D-Ala in the cell wall peptidoglycan by D-lactate
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