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Microbiology, 2021

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570 14 • Antimicrobial Drugs<br />

lactamase enzymes. Although they all share the same nucleus, various penicillins differ from each other in the structure of their R groups.<br />

Chemical changes to the R groups provided increased spectrum of activity, acid stability, and resistance to β-lactamase degradation.<br />

Drugs that Inhibit Bacterial Cell Wall Synthesis<br />

Mechanism of Action Drug Class Specific Drugs<br />

Natural or<br />

Semisynthetic<br />

Spectrum of Activity<br />

Penicillin G,<br />

penicillin V<br />

Natural<br />

Narrow-spectrum<br />

against gram-positive<br />

and a few gram-negative<br />

bacteria<br />

Penicillins<br />

Ampicillin,<br />

amoxicillin<br />

Semisynthetic<br />

Narrow-spectrum<br />

against gram-positive<br />

bacteria but with<br />

increased gram-negative<br />

spectrum<br />

Methicillin<br />

Semisynthetic<br />

Narrow-spectrum<br />

against gram-positive<br />

bacteria only, including<br />

strains producing<br />

penicillinase<br />

Interact directly with<br />

PBPs and inhibit<br />

transpeptidase activity<br />

Cephalosporin<br />

C<br />

Firstgeneration<br />

cephalosporins<br />

Natural<br />

Semisynthetic<br />

Narrow-spectrum<br />

similar to penicillin but<br />

with increased gramnegative<br />

spectrum<br />

Narrow-spectrum<br />

similar to cephalosporin<br />

C<br />

Cephalosporins<br />

Secondgeneration<br />

cephalosporins<br />

Semisynthetic<br />

Narrow-spectrum but<br />

with increased gramnegative<br />

spectrum<br />

compared with first<br />

generation<br />

Third- and<br />

fourthgeneration<br />

cephalosporins<br />

Semisynthetic<br />

Broad-spectrum against<br />

gram-positive and gramnegative<br />

bacteria,<br />

including some β-<br />

lactamase producers<br />

Fifthgeneration<br />

cephalosporins<br />

Semisynthetic<br />

Broad-spectrum against<br />

gram-positive and gramnegative<br />

bacteria,<br />

including MRSA<br />

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