These enzymes were named for their greater activity against cefotaxime than other oxyimino-beta-lactam substrates (eg, ceftazidime, ceftriaxone, or cefepime). Rather than arising by mutation, they represent examples of plasmid acquisition of beta-lactamase genes normally found on the chromosome of Kluyvera species, a group of rarely pathogenic commensal organisms. These enzymes are not very closely related to TEM or SHV beta-lactamases in that they show only approximately 40% identity with these two commonly isolated beta-lactamases. Despite their name, a few are more active on ceftazidime than cefotaxime. CTX-M-15 was recently found in bacterial strains expressing NDM-1 and were responsible for resistance to aztreonam.

Cephalosporins are a class of beta-lactam antibiotics, containing the beta-lactam ring fused with a dihydrothiazolidine ring. Together with cephamycins they belong to a sub-group called cephems. Cephalosporin are bactericidal, and act by inhibiting the synthesis of the peptidoglycan layer of bacterial cell walls. The peptidoglycan layer is important for cell wall structural integrity, especially in Gram-positive organisms.

Enzymatic inactivation of antibiotic to confer drug resistance.