A 22-year-old woman is brought to the emergency department because of a 2-day history of fever, intermittent rigors, and night sweats. She also has a 1-month history of progressive fatigue. The patient uses intravenous heroin and has been hospitalized several times due to skin and soft tissue infections. Cardiac auscultation shows a systolic ejection murmur, and subsequent echocardiography reveals a vegetative lesion of the aortic valve. Blood cultures from admission grow Enterococcus faecalis; subsequent testing reveals D-lactate rather than D-alanine as the terminal amino acid in the bacteria's pentapeptide peptidoglycan cell wall precursor. This substitution is likely to significantly decrease the efficacy of which of the following antibiotics?

Question

A 22-year-old woman is brought to the emergency department because of a 2-day history of fever, intermittent rigors, and night sweats. She also has a 1-month history of progressive fatigue. The patient uses intravenous heroin and has been hospitalized several times due to skin and soft tissue infections.  Cardiac auscultation shows a systolic ejection murmur, and subsequent echocardiography reveals a vegetative lesion of the aortic valve.  Blood cultures from admission grow Enterococcus faecalis; subsequent testing reveals D-lactate rather than D-alanine as the terminal amino acid in the bacteria's pentapeptide peptidoglycan cell wall precursor.  This substitution is likely to significantly decrease the efficacy of which of the following antibiotics?

Quizplus · Accepted Answer

Eductional Objective: Vancomycin binds to the terminal D-alanine-D-alanine in bacterial pentapeptide peptidoglycan subunits, which prevents transpeptidase from binding to the pentapeptide, thereby inhibiting cell wall cross-linking.  Resistance stems primarily from substitution of the terminal D-alanine with D-lactate, which prevents vancomycin binding.

A 22-Year-Old Woman Is Brought to the Emergency Department Because