Open Access Highly Accessed Research article

Antibiotic resistance, virulence determinants and production of biogenic amines among enterococci from ovine, feline, canine, porcine and human milk

Esther Jiménez1, Victor Ladero2, Irene Chico1, Antonio Maldonado-Barragán3, María López4, Virginia Martín15, Leonides Fernández15, María Fernández2, Miguel A Álvarez2, Carmen Torres4 and Juan M Rodríguez15*

Author Affiliations

1 Departamento de Nutrición, Bromatología y Tecnología de los Alimentos, Universidad Complutense de Madrid, Ciudad Universitaria, Avda. Puerta de Hierro, Madrid s/n. 28040, Spain

2 Instituto de Productos Lácteos de Asturias (IPLA-CSIC), Paseo Río Linares s/n 33300, Villaviciosa, Spain

3 Departamento de Biotecnología de Alimentos, Instituto de la Grasa-CSIC, Sevilla 41012, Spain

4 Área de Bioquímica y Biología Molecular, Universidad de La Rioja, Logroño, Spain

5 Probisearch. c/Santiago Grisolía, Tres Cantos 2. 28760, Spain

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BMC Microbiology 2013, 13:288  doi:10.1186/1471-2180-13-288

Published: 10 December 2013



Recent 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.


Samples 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.


Enterococci 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.

Enterococcus; Milk; Mammals; Virulence; Antibiotic resistance; Biogenic amines