Poirel, Laurent Ortiz de la Rosa, José Manuel Richard, Anaïs Aires-de-Sousa, Marta Nordmann, Patrice 2019-12-01 CTX-M-type extended-spectrum β-lactamases (ESBLs) are widespread among Enterobacterales strains worldwide. The most common variant is CTX-M-15, which hydrolyzes ceftazidime at a high rate but spares carbapenems. Here, we identified CTX-M-33, a point mutation derivative of CTX-M-15 (Asp to Ser substitution at Ambler position 109) that exhibited low carbapenemase activity. β-Lactamase CTX-M-33 was identified in a Klebsiella pneumoniae isolate, belonging to sequence type 405 and lacking the outer membrane protein OmpK36, that was resistant to broad-spectrum cephalosporins and β-lactam/β-lactamase inhibitor combinations and displayed decreased susceptibility to carbapenems. Comparative hydrolytic activity assays showed that CTX-M-33 hydrolyzed ceftazidime at a lower level than CTX-M-15 but significantly hydrolyzed meropenem. In addition, CTX-M-33 showed higher mutant prevention concentration values and a wider mutant selection window in the presence of meropenem, in accordance with its observed hydrolytic properties. Here, we identified the very first CTX-M enzyme possessing weak carbapenemase activity, which may correspond to an emerging phenomenon, considering its possible evolution from the widespread ESBL CTX-M-15. application/pdf https://folia.unifr.ch/global/documents/308393 https://folia.unifr.ch/documents/308393/files/nor_ccd.pdf eng info:eu-repo/semantics/altIdentifier/doi/10.1128/AAC.01515-19 info:eu-repo/semantics/openAccess License undefined Antimicrobial Agents and Chemotherapy. - 2019, vol. 63, no. 12, p. 10.1128/aac.01515-19 info:eu-repo/classification/udc/57 CTX-M-33 Is a CTX-M-15 derivative conferring reduced susceptibility to carbapenems http://purl.org/coar/resource_type/c_6501