CTXM

CTX-M is a family of beta-lactamase enzymes classified as extended-spectrum beta-lactamases (ESBLs). The bla_CTX-M genes encode enzymes that hydrolyze extended-spectrum cephalosporins, notably cefotaxime, and, to varying degrees, ceftazidime, reducing the effectiveness of many beta-lactam antibiotics against Enterobacterales and other Gram-negative bacteria. CTX-M enzymes are among the most common ESBLs reported in clinical isolates worldwide and are a major factor in antimicrobial resistance.

Origin and diversification. Most CTX-M enzymes originated from chromosomal beta-lactamases of Kluyvera spp. and were mobilized onto plasmids through genetic rearrangements, enabling rapid spread across species. The CTX-M family comprises multiple groups (for example CTX-M-1, CTX-M-2, CTX-M-8, CTX-M-9, CTX-M-25) with numerous variants such as CTX-M-15, CTX-M-14, CTX-M-27, and CTX-M-55. The CTX-M-15 variant is particularly widespread, with regional differences in prevalent variants.

Genetic mobility and epidemiology. CTX-M genes are often located on plasmids and linked to mobile elements such as ISEcp1, which promote transcriptional upregulation and transposition. This mobility facilitates dissemination among Enterobacterales, especially Escherichia coli and Klebsiella pneumoniae, in hospital and community settings, as well as in animal reservoirs and environmental sources. Global distribution continues to evolve with regional predominance of certain variants.

Clinical impact and detection. Infections caused by CTX-M–producing strains may limit the activity of third-generation cephalosporins, complicating treatment. Management often relies on carbapenems or alternative agents when susceptibility allows. Laboratory detection combines phenotypic ESBL testing with molecular methods (PCR and sequencing) to identify bla_CTX-M and determine the specific variant.

Prevention and surveillance. Public health surveillance tracks CTX-M prevalence and spread. Antimicrobial stewardship, infection control, and prudent antibiotic use in human and animal health are essential to limit dissemination of CTX-M–producing organisms.