A Preliminary Study on Antimicrobial Susceptibility of Staphylococcus spp. and Enterococcus spp. Grown on Mannitol Salt Agar in European Wild Boar (Sus scrofa) Hunted in Campania Region—Italy

SIMPLE SUMMARY: During the last decade, an increase in the European wild boar (Sus scrofa) population occurred; thus, over the years, wild boars have become an important potential carrier of pathogenic bacteria for both livestock animals and pets, but also for humans. Since antibiotic resistance has become one of the greatest challenges of global public health, the aim of the present study was to define the prevalence and the antibiotic resistance profiles of bacteria grown on the selective medium mannitol salt agar (MSA), isolated from nasal swabs of wild boars hunted in Campania Region (southern Italy). The most prevalent isolated bacteria were represented by the Staphylococcus spp. and Enterococcus spp. strains, which showed worrying antibiotic-resistant profiles. Consequently, constant surveillance of wild boars is strongly recommended, in order to assess their role as reservoirs of antibiotic resistant bacteria and as sentinels of a possible environmental contamination. ABSTRACT: The importance of wild boar lies in its role as a bioindicator for the control of numerous zoonotic and non-zoonotic diseases, including antibiotic resistance. Mannitol Salt Agar (MSA) is a selective medium used for isolation, enumeration, and differentiation of pathogenic staphylococci. Other genera such as Enterococcus spp. are also salt tolerant and able to grow on MSA. The present study focused on the identification, by matrix assisted laser desorption/ionization-time of flight mass spectrometry (MALDI-TOF-MS), of bacteria grown on MSA isolated from the nasal cavities of 50 healthy wild boars hunted in Campania Region (southern Italy) in the year 2019. In addition, the antimicrobial resistance phenotype of the isolated strains was determined by disk diffusion method. Among genus Staphylococcus, coagulase-negative Staphylococcus (CoNS) were the most common isolated species, with Staphylococcus xylosus as the most prevalent species (33.3%). Furthermore, Enterococcus spp. strains were isolated, and Enterococcus faecalis was the species showing the highest frequency of isolation (93.8%). For staphylococci, high levels of resistance to oxacillin (93.3%) were recorded. Differently, they exhibited low frequencies of resistance to tested non-β-lactams antibiotics. Among enterococci, the highest resistances were observed for penicillin (93.7%), followed by ampicillin (75%), and ciprofloxacin (68.7%). Interestingly, 43.7% of the isolated strains were vancomycin-resistant. In conclusion, this study reports the phenotypic antibiotic resistance profiles of Staphylococcus spp. and Enterococcus spp. strains isolated from nasal cavities of wild boars hunted in Campania Region, highlighting that these wild animals are carriers of antibiotic resistant bacteria.