Characterization of extended-spectrum beta-lactamase (ESBL) producing Escherichia coli from raw meat and comparison to human isolates

We selectively screened 153 food samples (raw meat) collected in supermarkets in Styria (Austria) to determine the rate of extended-spectrum beta-lactamase- (ESBL-) producing Escherichia coli. A high incidence of ESBL-producing E. coli was found in chicken meat (35.9%), while pork or beef were rarely contaminated with ESBL-producing strains. Genetic analyses revealed that CTX-M-1 was the prevalent enzyme among the food strains examined, while blaCTX-M-15-harboring isolates could not be found. In contrast, human stool isolates and isolates from patients suffering from community-acquired urinary tract infections mainly produced CTX-M-15 enzymes and CTX-M beta-lactamases of phylogenetic group 9. The pandemic ESBL-producing E. coli serotype 025:H4 was only detected in human urine samples of patients suffering from urinary tract infections. Susceptibility testing using Sensititre (R) microdilution minimum inhibitory concentration (MIC) plates revealed high resistance rates of food isolates against sulfamethoxazole, trimethoprim and tetracycline, antibiotics that may facilitate co-selection of ESBL. As bla(CTX-M-1) genes were also found in human stool isolates, it cannot be ruled out that ESBL-producing bacteria or ESBL genes are also transferred via the food chain.