The CTX-M beta-lactamase pandemic

Curr Opin Microbiol. 2006 Oct;9(5):466-75. doi: 10.1016/j.mib.2006.08.011. Epub 2006 Aug 30.


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.

Publication types

  • Research Support, Non-U.S. Gov't
  • Review

MeSH terms

  • Anti-Bacterial Agents / pharmacology
  • Bacteria / drug effects
  • Bacteria / enzymology*
  • Bacterial Infections / epidemiology
  • Bacterial Infections / microbiology*
  • Cross Infection / epidemiology
  • Cross Infection / microbiology
  • DNA Transposable Elements
  • Drug Resistance, Multiple, Bacterial
  • Endemic Diseases
  • Enterobacteriaceae Infections / microbiology
  • Escherichia coli / enzymology
  • Genes, Bacterial
  • Global Health
  • Humans
  • Integrons
  • Kluyvera / enzymology
  • Plasmids / genetics
  • beta-Lactamases / biosynthesis*
  • beta-Lactamases / genetics


  • Anti-Bacterial Agents
  • DNA Transposable Elements
  • beta-Lactamases