title: CTX-M-93, a CTX-M variant lacking penicillin hydrolytic activity.
abstract: Extended-spectrum β-lactamases (ESBLs) of the CTX-M type are increasingly being reported worldwide, with more than 90 known variants. Clinical Escherichia coli isolate Bre-1 was isolated in 2009 and displayed an unusual ESBL phenotype, made of a synergy image between expanded cephalosporins and clavulanic acid discs and susceptibility to penicillins. E. coli Bre-1 harbored a novel CTX-M-encoding gene, designated bla(CTX-M-93). CTX-M-93 differed from CTX-M-27 by only a single L169Q substitution. Compared to CTX-M-27, CTX-M-93 conferred higher MICs of ceftazidime for E. coli (MIC of 8 versus 1.5 μg/ml) and decreased MICs of other expanded-cephalosporins (MIC of cefotaxime of 1 versus 32 μg/ml) and penicillins (MIC of ticarcillin of 0.5 versus >256 μg/ml). A comparison of enzymatic properties revealed that the L169Q substitution led to a decreased Km for ceftazidime (25.5 versus 330 μM) but decreased hydrolytic activity against good substrates, such as cefotaxime (kcat of 0.6 versus 113 s(-1)), probably owing to the alteration of the omega loop positioning during the catalytic process. The blaCTX-M-93 gene was surrounded by the ISEcp1 and IS903 elements and inserted onto a 150-kb non-self-transferrable IncF-type plasmid. E. coli Bre-1 belongs to phylogroup D and is of multilocus sequence type (MLST) 624, a sequence type found only in rare Spanish CTX-M-14-producing E. coli isolates. We have characterized a novel CTX-M variant, CTX-M-93, lacking significant penicillin hydrolysis but with increased ceftazidime hydrolysis.
authors.affiliation: Service de Bactériologie-Virologie, INSERM U914, Emerging Resistance to Antibiotics, Hôpital de Bicêtre, Assistance Publique-Hôpitaux de Paris, Faculté de Médecine Paris-Sud, Le Kremlin-Bicêtre, France.
authors.forename: Laura
authors.initials: L
authors.lastname: Djamdjian
authors.forename: Thierry
authors.initials: T
authors.lastname: Naas
authors.forename: Didier
authors.initials: D
authors.lastname: Tandé
authors.forename: Gaelle
authors.initials: G
authors.lastname: Cuzon
authors.forename: Catherine
authors.initials: C
authors.lastname: Hanrotel-Saliou
authors.forename: Patrice
authors.initials: P
authors.lastname: Nordmann
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D002442:Ceftazidime / Q000494:pharmacology; D002511:Cephalosporins / Q000494:pharmacology; D004926:Escherichia coli / Q000187:drug effects / Q000201:enzymology* / Q000235:genetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010406:Penicillins / Q000378:metabolism*; D010802:Phylogeny; D016133:Polymerase Chain Reaction; D001618:beta-Lactamases / Q000235:genetics / Q000378:metabolism*
chemical_list: D000900:Anti-Bacterial Agents; D002511:Cephalosporins; D010406:Penicillins; D002442:Ceftazidime; D001618:beta-Lactamases