Phenotypic and genotypic characterization of Enterococcus spp. from yolk sac infections in broiler chicks with a focus on virulence factors

Bacterial infections of yolk sacs contribute to increased mortality of chicks, chronic infections during their rearing, or increased selection in the flock, which in turn leads to high economic losses in poultry production worldwide. The aim of this study was a phenotypic and genotypic characterization of enterococci isolated from yolk sac infections (YSI) of broiler chickens from Poland and the Netherlands. Biochemical, matrix-assisted laser desorption/ionization (MALDI)–time-of-flight (TOF) MS, and rpoA gene sequencing identification was performed. Moreover, phenotypic and genotypic characterization of virulence factors and analysis of the clonal relationship of isolates by MALDI-TOF MS and enterobacterial repetitive intergenic consensus—polymerase chain reaction (ERIC-PCR) were performed. The biochemical test identified 70 isolates as Enterococcus faecalis and 6 as Enterococcus mundtii. The results of MALDI-TOF MS were 100% concordant with those obtained by rpoA gene sequencing, and all 76 isolates were identified as E. faecalis. Differences were noted in the β-glucuronidase, β-glucosidase, α-galactosidase, phosphatase, melibiose, lactose, and raffinose tests that is going about the results of biochemical identification. None of the isolates were beta-hemolytic on blood agar in aerobic conditions, but all but one were gelatinase positive. Among biofilm-forming isolates (30/76; 39.5%), as many as 66.7% (20/30) were Polish E. faecalis strains. Most of the isolates carried virulence genes, that is gelE, ace, asa1, efaAfs, fsrA, fsrB, fsrC, cob, cpd, and ccf, but none had the hyl gene. Some isolates harbored cyl operon genes. One Polish strain (ST16) had all of the tested cyl genes and the esp gene, considered clinically important, and showed the highest biofilm-forming ability. Nearly 50% of the isolates showed close genetic relatedness in ERIC typing. In contrast with MALDI-TOF MS cluster analysis, ERIC-PCR results did not show a relationship with the origin of the strains. Using MALDI-TOF MS, 7 peaks were found in Polish and Dutch isolates, which may type them as species-specific biomarkers in E. faecalis from YSI.