CTXM9

CTXM9 is a variant within the CTX-M family of beta-lactamase enzymes, a subset of extended-spectrum beta-lactamases (ESBLs) produced by some Gram-negative bacteria. Like other CTX-M enzymes, CTXM9 hydrolyzes beta-lactam antibiotics such as cefotaxime and other third-generation cephalosporins, contributing to a multidrug-resistant phenotype in affected strains. Its activity can vary against different cephalosporins and is generally inhibited by beta-lactamase inhibitors to a limited extent.

The bla_CTX-M-9 gene encoding CTXM9 is typically located on plasmids, which facilitates horizontal transfer between bacteria. These genetic elements are often associated with mobile insertion sequences and transposons that promote dissemination within enteric flora. As a result, CTXM9 has been found in various Enterobacterales species, including Escherichia coli and Klebsiella pneumoniae, and has been identified in multiple geographic regions.

Clinically, infection or colonization with CTXM9-producing strains can lead to reduced susceptibility to many cephalosporins, complicating treatment choices. Carbapenems often remain effective, but reliance on these agents increases, underscoring the importance of susceptibility testing. Co-occurrence with other resistance determinants, such as additional ESBL genes or plasmid-borne resistance factors, can further limit therapeutic options.

Detection of CTXM9 involves phenotypic ESBL testing alongside molecular methods, such as PCR and sequencing, to identify the bla_CTX-M-9 allele. Accurate identification informs antibiotic stewardship and helps track epidemiological trends of ESBL-producing organisms.