High prevalence of Salmonella enterica subsp. diarizonae in tonsils of sheep at slaughter

The presence of Salmonella was studied in tonsils and feces of sheep and goats at slaughter using PCR and culturing. The isolates were further characterized using PFGE to get more information about the genetic diversity of Salmonella strains circulating among sheep and goats. Antimicrobial resistance was studied because resistance to multiple antimicrobial agents among Salmonella is increasing. The prevalence of Salmonella was 43% and 2% in the tonsils of sheep and goat, respectively. Salmonella was not detected in the feces of adult animals and only sporadically in the feces of juveniles (2%). S. enterica subsp. diarizonae 61:k:1,5,(7) was isolated from 20% of the sheep tonsils and 1% of the goat tonsils. In total, 9 genotypes were obtained with PFGE using SpeI, XbaI, NotI and XhoI restriction enzymes; however, one genotype was predominant. All strains were sensitive to most (13/16) of the antimicrobials. Resistance to sulfamethoxazole was high (95%). Three (15%) strains, which were isolated from lambs, were also resistant to colistin. No correlation between the antimicrobial resistance pattern and the genotype was noticed. These results demonstrate that slaughtered sheep are an important reservoir for S. enterica subsp. diarizonae 61:k:1,5,(7) carrying this pathogen frequently in the tonsils. Future studies are needed to elucidate the significance of the tonsils in the contamination of sheep carcasses and meat with Salmonella.