Beta-Lactamases cause resistance to penicillins and cephalosporins by

Penicillins and cephalosporins are called beta-Iactam drugs because of the impoance of the intact BETA-lactam ring for antimicrobial activity. -Lactamases inactivate these drugs by breaking the single bond in their BETA-lactam ring. BETA-Lactamases are coded for by either a transferable plasmid or by the genome of the organism. Plasmids are extrachromosomal genetic elements that may be transferred among unrelated bacteria. Ref: katzung 12th ed INtroduction to chemotherapy.