The emergence and dissemination of CTX-M-producing Escherichia coli sequence type 131 causing community-onset bacteremia in Israel.

Community-onset bloodstream infections caused by extended-spectrum β-lactamase-producing Escherichia coli (ESBL-EC-COBSIs) were investigated over a 7-year-period (2003-2009) in our institution. ESBL-EC-COBSI inclusion criteria were cefotaxime/ceftazidime non-susceptible blood isolates recovered during 48 h upon hospital admission. Forty-one isolates were molecularly characterized. Susceptibilities were determined (Vitek-2) and genotyping was performed [multilocus sequence typing (MLST)]. CTX-M genes were determined [polymerase chain reaction (PCR) and sequencing] and bla CTX-M-encoding plasmids (n = 10) were analyzed and compared. Phylogrouping and virulence genes were identified (PCR). The incidence rate of ESBL-EC-COBSIs has increased from 2.94 to 7.87 cases/10,000 admissions. All isolates were multidrug-resistant (MDR), displaying co-resistance to ciprofloxacin (93 %), trimethoprim-sulfamethoxazole (85 %), and gentamicin (51 %). MLST identified ten sequence types (STs), of which five were novel. ST131 accounted for 66 % of the cases (27/41), and dominated over the years (prevalence of 25 % in 2003 and 85 % in 2009). All isolates carried CTX-M genes with the following prevalence: bla CTX-M-2 (6/8; 75 %) in 2003; bla CTX-M-15 (9/13, 69 % in 2007); and bla CTX-M-15 (11/20, 55 %) and bla CTX-M-14 (7/20, 35 %) in 2009. bla CTX-M-15- and bla CTX-M-14-encoding plasmids harbored by ST131 differed. Of all isolates, 98 % belonged to virulent phylogroups B2 (28/41, 68 %) and D (12/41, 29 %), though ST131 isolates carried a higher number of virulence genes compared to other lineages (p < 0.05). The incidence of ESBL-EC-COBSIs increased 2.7-fold during the period 2003-2009. This increase appears to be related to the emergence and clonal expansion of bla CTX-M-15- or bla CTX-M-14-carrying ST131. The superiority of this virulent lineage should be further explored.