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Retired NBME 16 Answers

nbme16/Block 1/Question#43 (reveal difficulty score)
A 68-year-old woman is diagnosed with ...
Substitution of d-lactate for d-alanine in peptidoglycan ๐Ÿ” / ๐Ÿ“บ / ๐ŸŒณ / ๐Ÿ“–
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submitted by โˆ—fruitkebabs(34)
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Vancomycin binds to the terminal d-Ala, d-Ala of the peptide side chain of Peptidoglycan which is normally used to cross-link Peptidoglycan strands together. Since the d-Ala, d-Ala is not available to be crosslinked when it is bound by Vancomycin, the Peptidoglycan wall cannot be crosslinked properly, thus compromising its structural rigidity. Bacteria which switch the terminal d-Ala for a d-Lac are resistant to Vancomycin. Helpful Diagram on Wiki

FA2020, p190

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chaosawaits  But isn't impaired influx/increased efflux also a common method of resistance for Vancomycin? So how do you know the answer is not also "upregulation of rapid efflux pump"? +



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