Vancomycin is an antibiotic that has become critical for controllingpenicillin-r

Question

Vancomycinis an antibiotic that has become critical for controllingpenicillin-resistant bacteria. This large glycopeptide (molecularwt. = 1449) binds to cellwall precursors and interferes withpeptidoglycansynthesis.

The polymyxinsare a group of antibiotics that are particularly effective as atopical antibiotic against skin infections. These largepolypeptides (molecular wt. = 1202) can disrupt some bacterialmembranesby binding preferentially tolipid Amolecules.

NOTE: Bacillushas a Gram (+) type envelope; E.coli has a Gram (-) type envelopeand

Methanobacteriumisan Archaea. (Hint: think about cell envelopestructure).

Explanation / Answer

The Polymyxins act on lipid A.This lipid A is pesent only ingram negative organisms. As E.coli is gram negative polymyxins will act againstthem.The majority of bacilli are Gram positive and so vancomycinacts against them. so in graph A: Bacillus survival rate is 80 while E.coli is 20.That indicatesthat the antibiotic used are polymyxins.
In graph B: Bacillus survival rate is 30 while E.coli is 80.Sowe can safely assume that vancomycin was used.

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