Whole-genome sequencing analysis of highly prevalent Salmonella serovars in wild boars from a national park in Sardinia

The study investigated Salmonella prevalence in slaughtered wild boars from Asinara island National Park in Sardinia (Italy). Salmonella isolates were serotyped and the antimicrobial resistance profile was evaluated. Isolates were furthermore characterized with Whole Genome Sequencing. Additional analysis were performed in order to evaluate the microbial hygiene of wild boars carcasses. A total of 306 samples were tested for Salmonella presence, of which n. 270 were from n. 90 slaughtered wild boars and n. 36 were from slaughterhouse environment. Salmonella was detected in 32/90 (35.6%) colon content and 16/90 (17.8%) mesenteric lymph nodes samples. The overall prevalence of Salmonella carriers wild boars, either in colon content and/or lymph nodes, was 42/90 (46.7%) but only one animal was found positive at carcass level. Prevalence was not influenced (P > 0.05) by the age and the gender of the animals. Eight different Salmonella serotypes were identified between 50 isolates, with the most common ones being Abony and Newport. The sequence analysis showed that S. Abony and S. Newport strains clustered separately from public genomes. This finding refects the origin of the animals from the geographical closed environment of Asinara island. Moreover, sequence analysis showed high similarity between strains belonging to the same serovar. S. Derby and S. Agona strains exhibited phenotypic resistance to fosfomycin and harboured the fosA7 gene. The mean aerobic colony count and Enterobacteriaceae values showed a good hygiene level of the carcasses. This study demonstrated that Salmonella enterica is widespread in wild boar population of Asinara island and could play an important role in transmission to humans. The finding of Salmonella strains resistant to fosfomycin is of primary importance as this drug is used as an alternative treatment for infections caused by multi-drug resistant microorganisms.