Antimicrobial resistance and genetic diversity of Enterococcus faecalis from yolk sac infections in broiler chicks

Abstract

Despite restrictions on the use of antibiotics in poultry, the percentage of multidrug resistant bacteria, isolated from both adult birds and chicks, remains high. These bacteria can spread between countries via hatching eggs or chicks. Antibiotic resistant bacteria can also pose a threat to hatchery and farm workers or to consumers of poultry. The aim of the study was to perform a phenotypic and genotypic analysis of the drug resistance of E. faecalis isolates from yolk sac infections in broiler chicks from Poland and the Netherlands and to determine their genetic diversity. The tests revealed resistance to antibiotics from category D, that is, tetracycline (69.7%); category C - lincomycin (98.7%), erythromycin (51.3%), aminoglycosides (high-level streptomycin and kanamycin resistance - 10.5% and 3.95%, respectively), and chloramphenicol (7.9%); and category B - ciprofloxacin (25% with resistance or intermediate resistance). No resistance to penicillin, ampicillin, high-level gentamicin, tigecycline, or linezolid was noted. Various combinations of the erm(B), tet(M), tet(L), tet(O), ant(6)-Ia, aph(3')-IIIa, ant(4')-Ia, cat, and msr(A/B) genes were detected in all isolates (irrespective of the drug-resistance phenotype). Among isolates that carried the tet(M) and/or the tet(L) gene, 28% also had the Int-Tn gene, in contrast with isolates possessing tet(O). There were 28 sequence types and 43 PFGE restriction patterns. About 60% of isolates were of sequences types ST59, ST16, ST116, ST282, ST36, and ST82. Nine new sequence types were shown (ST836-ST844). In conclusion, broiler chicks can be a source of drug-resistant sequence types of E. faecalis that are potentially hazardous for people and animals. Restrictive programs for antibiotic use in broiler breeding flocks should be developed to decrease drug resistance in day-old chicks and reduce economic losses during rearing.

Keywords: Enterococcus faecalis; antibiotic resistance; broiler chicks; yolk sac infections.