Molecular diversity associated with the dissemination of CTX-M-15 beta-lactamase gene in blood culture isolates of Escherichia coli from Edinburgh

Background: Escherichia coli producing the CTX-M-15 beta-lactamase are a major cause of infection. We present the characterization of plasmids encoding the CTX-M-15 beta-lactamase gene, the genetic environment, and the mode of spread of this gene in blood culture isolates from a single hospital. Methods: Blood culture E. coli isolates with extended spectrum beta-lactamase (ESBL) phenotype were screened for the presence of the bla(CTX-M) gene, other ESBLs, and aac(6')-Ib-cr genes. The genetic environment of bla(CTX-M) was determined by DNA sequencing. Plasmids were classified by their incompatibility group from polymerase chain reaction (PCR) replicon typing. Plasmid numbers and sizing were assessed by alkaline lysis and S1 nuclease digestion. Genotyping of the strains was determined by pulsed-field gel electrophoresis (PFGE) and ST131 by allele-specific PCR. Results: Seven isolates had bla(CTX-M-15), with these isolates additionally having bla TEM (n = 5), bla OXA (n = 6), and aac(6')-Ib-cr (n = 6). Insertion sequence IS Ecp1 was found upstream of the bla(CTX-M) gene, and in 2 isolates, IS Ecp1 was found to be truncated with insertion sequence IS26. Plasmid replicon typing showed bla(CTX-M-15) genes were carried on the IncFII plasmid. All 7 isolates were associated with the O25b-ST131 clone. The PFGE banding pattern showed only 3 isolates were able to demonstrate clonality. Conclusions: This study shows the molecular diversity associated with the dissemination of bla(CTX-M-15) in a single Scottish hospital, which is largely due to horizontal transfer of multiresistance IncF plasmids rather than clonal spread. It demonstrates that more detailed information is needed to monitor these bacteria to control them appropriately.