Antimicrobial resistance and virulence factors of Streptococcus suis strains isolated from diseased pigs in southern Italy (Sardinia)

Streptococcus suis is a major swine pathogen responsible for important economic losses to the porcine industry worldwide. The objective of this study was to characterize strains of S suis isolated from dead piglets from farms located in southern Italy (Sardinia) between 2012 and 2014, by determining their genotype profiles, antimicrobial resistance profiles, and presence of associated virulence factors in order to evaluate a potential association between antimicrobial resistance serotypes and virulence factors. A total of 39 S suis isolates were examined for possession of virulence-associated factors using multiplex polymerase chain reaction assays. All isolates were tested for susceptibility to antimicrobial agents. Fisher’s exact test was performed in order to study the correlation between antimicrobial resistance and virulence factors epf+/epf-. Genotypes cps2+/epf+/sly+/mrp+/arcA+, cps2+/epf-/sly+/mrp+/arcA+, and cps2-/epf-/sly+/mrp+/arcA+ were identified, representing 18.0%, 74.6%, and 7.4% of the isolates, respectively. A high frequency of resistance was observed for tetracycline (88.9%) and erythromycin (38.9%). No correlation between the virulence factor epf and resistance to multiple antibiotics was found.