Detection of chromosomal blaCTX-M-15 in Escherichia coli O25b-B2-ST131 isolates from the Kinki region of Japan.

Escherichia coli O25b-B2-ST131 isolates harbouring bla(CTX-M-15) are distributed worldwide. The bla(CTX-M-15) transposition unit has often been found on plasmids and the genetic contexts have been examined; however, less is known about the frequency and contexts of the bla(CTX-M-15) transposition unit on the chromosome. This study was performed to determine the chromosomal location of the bla(CTX-M-15) transposition unit and to analyse the molecular structure of the region surrounding the bla(CTX-M-15) transposition unit in E. coli O25b-B2-ST131 isolates. Twenty-two E. coli O25b-B2-ST131 strains harbouring bla(CTX-M-15) that had been isolated from university hospital patients and nursing home residents in the Kinki region of Japan were examined. Inverse PCR (iPCR) targeting bla(CTX-M-15) was performed to classify the molecular structure of the region surrounding the bla(CTX-M-15) transposition unit. The isolates were classified into nine types (types A-I) considering the iPCR results; type A was the most prevalent type (13/22 isolates). Sequences of the iPCR-amplified DNA fragments showed that the bla(CTX-M-15) transposition unit consisted of ISEcp1, bla(CTX-M-15) and orf477Δ. A homology search of the obtained sequences showed that the bla(CTX-M-15) transposition unit was inserted into different chromosomal regions in eight of the nine classified types. Although 21 of the 22 E. coli isolates possessed chromosomally located bla(CTX-M-15) transposition units, clonal spread was not evident on pulsed-field gel electrophoresis (PFGE) analysis. Taken together, these data indicate that certain E. coli O25b-B2-ST131 strains harbouring chromosomal bla(CTX-M-15) have emerged and spread in the Kinki region of Japan.

Prevalence of and risk factors associated with faecal carriage of CTX-M ß-lactamase-producing Enterobacteriaceae in rural Thai communities.

OBJECTIVES: To determine the prevalence of CTX-M ß-lactamase-producing Enterobacteriaceae and to study the risk factors associated with faecal carriage in asymptomatic rural Thai people. METHODS: In all, 417 stool samples were obtained from rural Thai people and screened for extended-spectrum ß-lactamases (ESBLs) using MacConkey agar supplemented with 2 mg/L cefotaxime. Results were confirmed using cefotaxime and ceftazidime with and without clavulanic acid. The bla(CTX-M) genes were identified and genotyped using PCR with bacterial DNA samples. Multivariate analysis was performed to investigate risk factors associated with the faecal carriage of CTX-M producers. RESULTS: The prevalence of CTX-M-type ESBL-producing Enterobacteriaceae was 65.7%. The CTX-M-9 group (60.6%) was dominant, followed by the CTX-M-1 group (38.7%). Most of the bacteria were Escherichia coli (85.4%) and Klebsiella pneumoniae (4.7%). Of a total of 234 E. coli strains, 48.7% belonged to phylogenetic group A, 28.6% to group B1, 15.8% to group D and 6.8% to group B2. Most CTX-M producers were susceptible to carbapenems and amikacin, but resistant to tetracycline and gentamicin. In a multivariate logistic regression model, better education status (OR 2.245; 95% CI 1.297-3.884), history of hospitalization (OR 1.643; 95% CI 1.036-2.603) and the use of antibiotics within the last 3 months (OR 1.883; 95% CI 1.221-2.903) were independently associated with faecal carriage. CONCLUSIONS: Faecal carriage of CTX-M-type ESBL-producing Enterobacteriaceae among asymptomatic individuals in rural Thailand remains alarmingly high, and previous antibiotic use and a history of hospitalization may contribute to its dissemination.