Is staphylococci population from milk of healthy goats safe?

• S. epidermidis, S. caprae, S. aureus and S. simulans were identified in goat milk.
• S. simulans and S. epidermidis were the most frequent staphylococci in goat milk.
• Antibiotic resistances were notably higher for S. epidermidis and S. aureus strains.
• Hemolysin genes were found in a high number of S. epidermidis and S. aureus strains.
• S. epidermidis and S. aureus strains could constitute a reservoir of safety traits.

The aim of this study was to assess the species and the genetic diversity of the staphylococci population in raw milk from healthy goats. Isolates representative of all genotypes were screened for their potential pathogenicity by the occurrence of some relevant safety-related properties, such as antibiotic resistance, presence of virulence factor genes, biofilm formation ability and biogenic amine production. A total of 314 staphylococci were isolated, and randomly amplified polymorphic DNA-PCR analysis displayed 48 genotypes. Isolates were identified as belonging to S. epidermidis (87.5%), S. caprae (6.2%), S. aureus (4.2%) and S. simulans (2.1%) species.The antibiotic resistance varied strongly with strains, with S. epidermidis and S. aureus strains showing resistance to more number of antibiotics. A high occurrence of strains harbouring hemolysin genes was also found in both species. On the contrary, none of the strains assayed harboured enterotoxin or amino acid decarboxylase genes, and, although a moderate or high biofilm formation was observed in 29% of the strains, they did not harbour icaA or icaD genes. This study gives a first and extensive picture of safety-related properties within Staphylococcus species isolated from milk of healthy goats, displaying that these species can act as a reservoir for spreading genes related to safety.