Genetic background of Escherichia coli and extended-spectrum β-lactamase type

To assess the implication of the genetic background of Escherichia coli strains in the emergence of extended-spectrum beta-lactamases (ESBL), 55 TEM-, 52 CTX-M-, and 22 SHV-type ESBL-producing clinical isolates involved in various extraintestinal infections or colonization were studied in terms of phylogenetic group, virulence factor (VF) content (pap, sfa/foc, hly, and aer genes), and fluoroquinolone resistance. A factorial analysis of correspondence showed that SHV type, and to a lesser extent TEM type, were preferentially observed in B2 phylogenetic group strains that exhibited numerous VFs but were fluoroquinolone-susceptible, whereas the newly emerged CTX-M type was associated with the D phylogenetic group strains that lacked VF but were fluoroquinolone-resistant. Thus, the emergence of ESBL-producing E. coli seems to be the result of complex interactions between the type of ESBL, genetic background of the strain, and selective pressures in ecologic niches.