Extended-spectrum beta-lactamases (ESBL) in Escherichia coli isolated from poultry.

Increasing prevalence of extended-spectrum beta-lactamases (ESBLs)-producing Escherichia coli has been reported in poultry over the past decade. ESBLs are an heterogeneous group of enzymes which confer resistance to most beta-lactam antimicrobials, including third and fourth generation cephalosporins; their activity is decreased by beta-lactamase inhibitors such as clavulanic acid. ESBLs-producing isolates are often associated with resistance to a large number of non-beta lactam antimicrobials, and with infections extremely difficult to treat. Typically, ESBLs are located on mobile genetic elements that can be easily spread both clonally and horizontally between different bacterial species. The zoonotic risk derived from the emergence of ESBL producing-E. coli in animals has been hypothesized by various authors. The screening and confirmatory tests for ESBLs production were performed by the disk diffusion method, as recommended by the CLSI guidelines, in 257 E. coli of poultry origin. Cefpodoxime, ceftazidime and cefotaxime disks were used for the initial screening test to identify potentially ESBLs producing isolates, while ceftazidime and cefotaxime both combined with clavulanic acid were used to confirm ESBLs production. The difference of the inhibition zone diameters greater than 5 mm for any cephalosporin/ clavulanic acid combination, vs the corresponding cephalosporin alone, was considered indicative of ESBL production. Thirty two out of 257 E. coli isolates (12%) were identified as potential ESBLs-producers by the initial screening test, while the large majority of isolates (88%) resulted in ESBLs-non producers. Among those putative ESBLs-producers, 25 isolates were confirmed. The remaining 7 isolates, showing a difference smaller than 5 mm, were not confirmed.