Abstract
BackgroundRecent studies have shown that mammalian milk represents a continuous supply of commensal bacteria, including enterococci. The objectives of this study were to evaluate the presence of enterococci in milk of different species and to screen them for several genetic and phenotypic traits of clinical significance among enterococci.ResultsSamples were obtained from, at least, nine porcine, canine, ovine, feline and human healthy hosts. Enterococci could be isolated, at a concentration of 1.00 × 102 -1.16 × 103 CFU/ml, from all the porcine samples and, also from 85, 50, 25 and 25% of the human, canine, feline and ovine ones, respectively. They were identified as Enterococcus faecalis, Enterococcus faecium, Enterococcus hirae, Enterococcus casseliflavus and Enterococcus durans. Among the 120 initial enterococcal isolates, 36 were selected on the basis of their different PFGE profiles and further characterized. MLST analysis revealed a wide diversity of STs among the E. faecalis and E. faecium strains, including some frequently associated to hospital infections and novel STs. All the E. faecalis strains possessed some of the potential virulence determinants (cad, ccf, cob, cpd, efaAfs, agg2, gelE, cylA, espfs) assayed while the E. faecium ones only harboured the efaAfm gene. All the tested strains were susceptible to tigecycline, linezolid and vancomycin, and produced tyramine. Their susceptibility to the rest of the antimicrobials and their ability to produce other biogenic amines varied depending on the strain. Enterococci strains isolated from porcine samples showed the widest spectrum of antibiotic resistance.ConclusionsEnterococci isolated from milk of different mammals showed a great genetic diversity. The wide distribution of virulence genes and/or antibiotic resistance among the E. faecalis and E. faecium isolates indicates that they can constitute a reservoir of such traits and a risk to animal and human health.
Highlights
Recent studies have shown that mammalian milk represents a continuous supply of commensal bacteria, including enterococci
Natural lactation provides a wide variety of short- and long-term health benefits, being a critical period for mammals’ growth and development; precocious weaning is associated with high mortality and morbidity rates, in those species in which IgG transfer mainly occurs through maternal milk [1]
No colonies were detected on Violet Red Bile Agar (VRBA) plates, which confirmed the hygienic collection of the milk samples
Summary
Recent studies have shown that mammalian milk represents a continuous supply of commensal bacteria, including enterococci. Fresh mammalian milk from a given species usually fulfils the nutritional requirements of the neonates of such species and, protects them against infectious diseases. Genome sequencing of a high number of diverse Enterococcus faecium strains has been applied to resolve the lineage responsible for epidemic and/or multidrugresistant infections from other strains, and to measure the evolutionary distances between groups [24]. Such approach has shown that each evolutionary bifurcation has been accompanied by the acquisition of new metabolic and colonization traits on mobile elements and genome remodeling associated with the insertion and movement of such elements. Diversity within such enterococcal species, in terms of sequence divergence as well as gene content, may span a range usually associated with speciation [24]
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