Introduction Enterococci are widespread, being part of the bacterial flora of humans and animals. The food chain can be therefore considered as the main route of transmission of antibiotic resistant bacteria between the animal and human populations. Milk in particular represents a source from which resistant bacteria can enter the human food chain. The aim of the study was to determine the occurrence and resistance to antimicrobial agents of Enterococcus spp. strains isolated from raw goat’s milk samples. Material and Methods A total of 207 goat’s milk samples were collected. Samples were cultivated on selective media and confirmed as E. faecium or E. faecalis and screened for selected resistance genes by PCR. Drug susceptibility determination was performed by microdilution on Sensititre EU Surveillance Enterococcus EUVENC Antimicrobial Susceptibility Testing (AST) Plates and Sensititre US National Antimicrobial Resistance Monitoring System Gram Positive CMV3AGPF AST Plates. Results Enterococcal strains totalling 196 were isolated, of which 40.8% were E. faecalis and 15.3% were E. faecium. All tested isolates were susceptible to linezolid, penicillin and tigecycline. For most other antimicrobials the prevalence of resistance was 0.5–6.6% while high prevalence of quinupristin/dalfopristin (51.5%), tetracycline (30%) and lincomycin (52%) resistance was observed. Conclusion This study affords better knowledge concerning the safety of raw goat’s milk in terms of the enterococci possible to isolate from this foodstuff. It seems that enterococci in milk are still mostly susceptible to antimicrobials of major concern as multiply resisted drugs, such as gentamycin and vancomycin. However, the presence of multi-resistant strains in goat milk is cause for apprehension.

This study attempts to present the antimicrobial resistance, virulence and resistance genes of Enterococcus faecalis and Enterococcus faecium isolated from raw goat’s and sheep’s milk and cheese. Strains were identified by PCR. The dominant species was E. faecalis (77.8%) and was most often isolated from raw goat’s milk. The percentage of antimicrobial-resistant E. faecalis isolates was higher than that of E. faecium isolates, the former most frequently resistant to lincomycin (98%), tetracycline (63%) and streptomycin (16%). Fourteen (22.3%) E. faecalis and 2 (11.1%) E. faecium isolates were identified as multidrug-resistant (MDR). All MDR E. faecalis strains also had virulence genes, whereas one of the two E. faecium strains had them. The most prevalent virulence genes in E. faecalis isolates were asa1 (69.8%) and gelE (57.1%). The most prevalent resistance genes found in both bacterial species were tet(M) (43.2%) and vgaA (22.2%). Enterococci from dairy products are confirmed to be a potential source of the spread of antimicrobial resistance, MDR strains, and virulence and resistance genes. This study highlights several aspects of the virulence and pathogenicity of E. faecalis and E. faecium isolated from dairy products—aspects which are indications for their ongoing monitoring.

Proficiency testing (PT) is an important tool for evaluation of the competences of laboratories which test milk for residues of antimicrobial substances. It also warrants the reliability of the obtained test results, which is important to the clients of a laboratory. In 2017–2021, the Polish National Reference Laboratory organized 10 rounds of proficiency testing on raw milk samples according to the ISO/IEC 17043 standard. The milk samples were fortified with selected antimicrobial substances. All participating laboratories used commercial receptor and/or microbiological diagnostic kits in the proficiency tests. The results obtained by the laboratories were compared to assigned results and were defined as compliant or non-compliant. In total, 7533 results were obtained, and 104 (1.4%) were assessed as non-compliant. The percentage of laboratories which obtained a positive result in proficiency tests ranged by testing round from 81.8% to 100%. Based on proficiency testing results, it can be concluded that laboratories carry out tests correctly. The proven proficiency by a laboratory increases the confidence of its clients in its service of antimicrobial residue monitoring in milk.