title: The CTX-M beta-lactamase pandemic.
abstract: In the past decade CTX-M enzymes have become the most prevalent extended-spectrum beta-lactamases, both in nosocomial and in community settings. The insertion sequences (ISs) ISEcp1 and ISCR1 (formerly common region 1 [CR1] or orf513) appear to enable the mobilization of chromosomal beta-lactamase Kluyvera species genes, which display high homology with blaCTX-Ms. These ISs are preferentially linked to specific genes: ISEcp1 to most blaCTX-Ms, and ISCR1 to blaCTX-M-2 or blaCTX-M-9. The blaCTX-M genes embedded in class 1 integrons bearing ISCR1 are associated with different Tn402-derivatives, and often with mercury Tn21-like transposons. The blaCTX-M genes linked to ISEcp1 are often located in multidrug resistance regions containing different transposons and ISs. These structures have been located in narrow and broad host-range plasmids belonging to the same incompatibility groups as those of early antibiotic resistance plasmids. These plasmids frequently carry aminoglycoside, tetracycline, sulfonamide or fluoroquinolone resistance genes [qnr and/or aac(6')-Ib-cr], which would have facilitated the dissemination of blaCTX-M genes because of co-selection processes. In Escherichia coli, they are frequently carried in well-adapted phylogenetic groups with particular virulence-factor genotypes. Also, dissemination has been associated with different clones (CTX-M-9 or CTX-M-14 producers) or epidemic clones associated with specific enzymes such as CTX-M-15. All these events might have contributed to the current pandemic CTX-M beta-lactamase scenario.
authors.affiliation: Servicio de Microbiología, Hospital Ramón y Cajal, 28034-Madrid, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Cantón
authors.forename: Teresa M
authors.initials: TM
authors.lastname: Coque
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D001419:Bacteria / Q000187:drug effects / Q000201:enzymology*; D001424:Bacterial Infections / Q000453:epidemiology / Q000382:microbiology*; D003428:Cross Infection / Q000453:epidemiology / Q000382:microbiology; D004251:DNA Transposable Elements; D024901:Drug Resistance, Multiple, Bacterial; D019353:Endemic Diseases; D004756:Enterobacteriaceae Infections / Q000382:microbiology; D004926:Escherichia coli / Q000201:enzymology; D005798:Genes, Bacterial; D014943:Global Health; D006801:Humans; D032023:Integrons; D044086:Kluyvera / Q000201:enzymology; D010957:Plasmids / Q000235:genetics; D001618:beta-Lactamases / Q000096:biosynthesis* / Q000235:genetics
chemical_list: D000900:Anti-Bacterial Agents; D004251:DNA Transposable Elements; D001618:beta-Lactamases