OBJECTIVES: to assess the frequency and diversity of extended-spectrum β-lactamases (ESBLs) in Enterobacteriaceae isolates in Belgium.

METHODS: during 2006 and 2008, non-duplicate clinical isolates of Enterobacteriaceae resistant to ceftazidime and/or cefotaxime were collected in 100 Belgian hospitals. ESBL production was confirmed by phenotypic and genotypic tests. MICs of 13 antimicrobial agents were determined by Etest. ESBL-encoding genes were identified by PCR sequencing and the bla(CTX-M) environment was characterized by PCR mapping. Selected isolates were genotyped by PFGE, multilocus sequence typing analysis and phylogenetic grouping by PCR.

RESULTS: overall, 733 isolates were confirmed as ESBL producers. Carbapenems and temocillin were active against ≥ 95% of all tested isolates. Co-resistance to co-trimoxazole and to ciprofloxacin was found in almost 70% and 80% of the strains, respectively. Overall, Escherichia coli (49%), Enterobacter aerogenes (32%) and Klebsiella pneumoniae (9%) represented the most prevalent species. Isolates harboured predominantly TEM-24 (30.7%), CTX-M-15 (24.2%) and TEM-52 (12.1%). Compared with 2006, the proportion of CTX-M-type enzymes increased significantly in 2008 (54% versus 23%; P < 10(-6)), mostly linked to a rising proportion of CTX-M-15-producing E. coli. TEM-24 decreased (19% in 2008 versus 43% in 2006; P < 10(-6)) during the same period, while the prevalence of TEM-52 remained unchanged (10% in 2008 versus 14% in 2006; not significant). Over 80% of the CTX-M-15-producing E. coli isolates clustered into a single PFGE type and phylogroup B2, corresponding to the sequence type (ST) 131 clone. Intra- and inter-species gene dissemination (CTX-M-15, CTX-M-2 and CTX-M-9) and wide epidemic spread of the CTX-M-15-producing E. coli ST131 clone in several Belgian hospitals were observed.

CONCLUSIONS: the rapid emergence of multiresistant CTX-M-15-producing E. coli isolates is of major concern and highlights the need for further surveillance in Belgium.