Abstract
Virulence-associated traits have frequently been studied in enterococci and are considered to contribute towards the pathogenicity of infections. In the present study, Enterococcus isolates were collected during diagnostic investigations from meat turkeys in Germany. Twenty-eight isolates of three different Enterococcus species were analyzed for five selected putative virulence traits to understand their potential role in the pathogenicity using the chicken embryo lethality assay. Ten E. faecalis, ten E. faecium, and eight E. gallinarum isolates were examined for the presence of common virulence genes and their phenotypic expression, namely, the cytolysin operon, five individual cyl genes (cylLL, cylLS, cylM, cylB, and cylA), gelatinase (gelE), hyaluronidase (hylEfm), aggregation substance (asa1), and enterococcal surface protein (esp). The Enterococcus isolates showed significant species-dependent differences in the presence of genotypic traits (p < 0.001 by Fisher's exact test; Cramer's V = 0.68). At least one gene and up to three virulence traits were found in E. faecalis, while six E. faecium isolates and one E. gallinarum isolate did not display any virulence-associated pheno- or genotype. More than half of the Enterococcus isolates (n = 15) harbored the gelE gene, but only E. faecalis (n = 10) expressed the gelatinase activity in vitro. The hylEfm gene was found in five E. gallinarum isolates only, while seven isolates showed the hyaluronidase activity in the phenotypic assay. In Cramer's V statistic, a moderate association was indicated for species (V ≤ 0.35) or genotype (V < 0.43) and the results from the embryo lethality assay, but the differences were not significant. All E. gallinarum isolates were less virulent with mortality rates ranging between 0 and 30%. Two E. faecalis isolates were highly virulent, harboring the whole cyl-operon as well as gelE and asa1 genes. Likewise, one E. faecium isolate caused high embryo mortality but did not harbor any of the investigated virulence genes. For the first time, Enterococcus isolates of three different species collected from diseased turkeys were investigated for their virulence properties in comparison. The results differed markedly between the Enterococcus species, with E. faecalis harboring the majority of investigated genes and virulence traits. However, the genotype did not entirely correlate with the phenotype or the isolates' virulence potential and pathogenicity for chicken embryos.
Highlights
Enterococci are opportunistic bacterial pathogens that belong to the gastrointestinal flora of mammals and birds
At least one of the virulence genes was found in E. faecalis, while six E. faecium isolates, two E. gallinarum isolates, and the corresponding
28 Enterococcus isolates from poults and subadult turkeys were investigated for five common virulence traits, namely, the cytolysin toxin, the lytic enzymes gelatinase and hyaluronidase, and the aggregation substance and enterococcal surface proteins. ese traits have been selected because they seem to be more prevalent in the clinical course of Enterococcus isolates [17, 18, 40]. e aim was to understand genotype-phenotype correlations and their potential role in pathogenicity using the chicken embryo lethality assay
Summary
Enterococci are opportunistic bacterial pathogens that belong to the gastrointestinal flora of mammals and birds. Enterococcus faecalis and E. cecorum are responsible for the majority of enterococcal infections in poultry. Clinical infections with E. cecorum became more prevalent over the past years and are responsible for severe inflammatory lesions of bones, joints, and internal organs in various poultry species including turkeys [5]. Enterococci are a common cause of nosocomial infections in humans, and BioMed Research International therapeutic options are impaired by multiresistant strains [6, 7]. Resistance genes as well as virulence-associated genes are located on plasmids or transposons and can be transferred between different Enterococcus species and to other bacteria [8]. Enterococcal colonization of host tissues is facilitated by degradation of hyaluronic acids [11], encoded by the hyaluronidase gene hylEfm [12], as well as by different adhesins. Aggregation substance, encoded by asa1 [13], is a group of surface proteins that promotes bacterial adherence to renal tubular cells [14] and internalization by intestinal cells [15], while the enterococcal surface protein, encoded by esp, is associated with bacterial biofilm formation [16]
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