Purpose: The objective of this study was to analyze the prevalence of ESBL-producing Enterobacteriaceae (ESBL-E) and ESBL-E. coli on cow/calf operations located in Florida to understand the spread of ESBLs among food animals and to characterize the ESBLs isolated from animals.
Methods: One thousand ninety-six samples were collected from 17 farms including feces of calves and cows, soil, water, and forage. ESBL-E and ESBL-E. coli were isolated by plating on MacConkey agar containing cefotaxime (four µg/ml) and ChromAgar E. coli media. The prevalence was calculated by dividing the number of positive samples by the total number of samples and the confidence interval (CI) was estimated with a 95% confidence level. The ESBL genes were identified using PCR. Minimum inhibitory concentration (MIC) to cefotaxime and antibiotic susceptibility against 13 different antibiotics were determined to characterize ESBL-E.coli.
Results: All the farms had ESBL-E, the prevalence ranged between 13.15% and 63.63%. The average concentration of ESBL-E was 1.68 log CFU/g of feces (95% CI: 1.6 to 1.77). Sixty-five percent (11 of 17) of beef farms had ESBL-E. coli in the majority of the samples (feces, forage, and soil), except water sample. The average prevalence and concentration were 7.42% and 1.56 log CFU/g of feces (95% CI: 1.37 to 1.74), respectively. The CTX-M gene was the most predominant ESBL gene type. Furthermore, all isolates showed a MIC of cefotaxime ≥16 µg/ml and multidrug resistance, suggesting that it could be a potential life-threatening factor.
Significance: Our results provide critical knowledge to better understand the prevalence and characteristics of ESBLs on cattle operations in Florida where antibiotics were not extensively used for prophylactic purpose.