This class of antibiotic includes the penicillins, cephalosporins, carbapenems, and monobactams, which inhibit the formation of the bacterial cell wall by inhibiting the transpeptidation step in peptidoglycan synthesis. These antibiotics can also bind penicillin-binding proteins and stimulate autolysins, which then lyse the bacterial cell. Resistance to b-lactam antibiotics is commonly mediated by enzymatic inactivation of the antibiotic by a class of enzymes called p-lactamases. The presence of a b-lactamase can be overcome by combining a b-lactam antibiotic with a b-lactamase inhibitor such as clavulanic acid or sulbactam. However, bacteria can also become resistant to these b-lactamase inhibitors. Resistance to p-lactams can also be conferred by mutations to the penicillin-binding proteins, which results in reduced affinity of these proteins for the p-lactam antibiotic. Finally, bacteria can alter the cell wall to reduce the uptake of p-lactams, or use an active efflux pump system to remove the antibiotic from the cytoplasm, although these mechanisms are rare.
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