Seasonal diversity and safety evaluation of enterococci population from goat milk in a farm
2016
Ruiz, Patricia | Pérez-Martín, Fátima | Seseña, Susana | Palop, María Llanos
The presence and genetic diversity of enterococci in raw goat milk sampled in a farm during consecutive seasons were evaluated. Representative strains were screened for virulence determinants, susceptibility to antibiotics and the presence of genes involved in biogenic amine production. Counts of enterococci ranged between 2.80 × 10¹ and 2.50 × 10³ cfu.mL–¹ with summer samples showing the highest counts and winter samples the lowest. A total of 695 enterococci were isolated and genotyped. One hundred and thirty-three representative isolates from genotypes obtained in randomly amplified polymorphic DNA-polymerase chain reaction (RAPD-PCR) analysis were identified as belonging to Enterococcus faecium (62.9%), Enterococcus faecalis (28.2%) and Enterococcus hirae (8.9%) species. A higher number of genotypes was observed in the summer and spring samples. The occurrence of antibiotic resistance and virulence genes was strain dependent, although the presence of genes did not always imply resistance, as occurred for vancomycin. All three species showed a high percentage of resistance to tetracycline. Strains from the warmer seasons (spring, summer and autumn) were resistant to a higher number of antibiotics and harboured a higher number of antibiotic resistance and virulence genes. All the strains produced tyramine, while only one E. hirae strain from a spring sample produced putrescine. The feed regime of goats during the warm seasons was the main difference between samples and thus, it could be proposed that the feed is responsible for the differences in the results between seasons.
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