Occurrence and characteristics of extended-spectrum β-lactamase (ESBL) producing Enterobacteriaceae in food producing animals, minced meat and raw milk

As many as 15.3% of the porcine, 13.7% of the bovine, 8.6% of the sheep and 63.4% of the chicken fecal samples yielded ESBL producers after an enrichment step. In contrast, none of the minced meat, none of the bulk tank milk samples and only one of the mastitis milk samples contained ESBL producing strains. Of the total of 91 isolates, 89 were E. coli, one was Citrobacter youngae and one was Enterobacter cloacae. PCR analysis revealed that 78 isolates (85.7%) produced CTX-M group 1 ESBLs while six isolates (6.6%) produced CTX-M group 9 enzymes. Five detected ESBLs (5.5%) belonged to the SHV group and 2 isolates (2.2%) contained a TEM-type enzyme. A total of 27 CTX-M producers were additionally PCR-positive for TEM-beta-lactamase. The ESBL-encoding genes of 53 isolates were sequenced of which 34 produced CTX-M-1, 6 produced CTX-M-14, 5 produced CTX-M-15 and also 5 produced SHV-12. Two isolates produced TEM-52 and one isolate expressed a novel CTX-M group 1 ESBL, CTX-M-117. One isolate--aside from a CTX-M ESBL-- contained an additional novel TEM-type broad-spectrum beta-lactamase, TEM-186.The relatively high rates of ESBL producers in food animals and the high genetic diversity among these isolates are worrisome and indicate an established reservoir in farm animals.Antimicrobial resistance in bacteria has emerged as a problem in both human and veterinary medicine. One of the currently most important resistance mechanisms in Enterobacteriaceae, which reduces the efficacy even of modern expanded-spectrum cephalosporins (except cephamycins and carbapenems) and monobactams is based on plasmid-mediated production of enzymes that inactivate these compounds by hydrolyzing their β-lactam ring. Such resistance is encoded by an increasing number of different point-mutational variants of classical broad-spectrum β-lactamases (BSBL). These variants are called extended spectrum β-lactamases (ESBL): most are derivates of TEM and SHV β-lactamase families, whereas other groups, such