Antibiotic resistance and mechanisms implicated in fecal enterococci recovered from pigs, cattle and sheep in a Portuguese slaughterhouse

Abstract

A total of 194 enterococcal isolates were recovered from 198 fecal samples of pigs, cattle, and sheep obtained in a Portuguese slaughterhouse. The enterococcal species most prevalent were Enterococcus faecium and E. hirae. High percentages of resistance were detected for tetracycline in pig isolates (95.7%), sheep isolates (76.7%), and cattle isolates (49%); erythromycin resistance was higher in pig isolates than in cattle or sheep isolates. Intermediate level of resistance was obtained to quinupristin/dalfopristin in all animal isolates (15.1–23.5%). High-level resistance to aminoglycosides was detected, HLR-S and -K was higher in pig isolates (44.3 and 32.9%, respectively) compared with cattle or sheep isolates, and modest percentages of HLR-G were obtained in pig and cattle isolates (7.1 and 3.9%, respectively). The aac(6`)-aph(2”), aph(3`)-IIIa, ant(6)-Ia, cat(A), erm(B), and tet(M) genes were demonstrated in most of the gentamycin-, kanamycin-, streptomycin-, chloramphenicol-, erythromycin- and tetracycline-resistant isolates, respectively. The association between the tet(M) gene and Tn916/Tn1545-like or Tn5397-like transposons was detected in 30.8 and 11.2% of the isolates, respectively. Food animals could be a reservoir for antibiotic resistance genes, and slaughterhouse cross-contamination of animals carcasses may be a food safety risk.