Clinically relevant multidrug resistant Salmonella enterica in swine and meat handlers at the abattoir

The presence of multidrug resistant (MDR) Salmonella serotypes in slaughtered swine, carcasses, meat and meat handlers is scarcely evaluated. Recently we demonstrated that diverse Salmonella serotypes are frequently present in swine, pork meat and carcasses, and meat handlers at Portuguese abattoirs. Here we have characterized their antibiotic resistance phenotypes and genotypes, helping elucidate the flow of MDR Salmonella in the food chain. Testing 60 Salmonella isolates from different serotypes, the highest frequencies of resistance were observed for tetracycline (T) [70% (n = 42/60), tet(A)/tet(B)/tet(G)], streptomycin (S) [63% (n = 38/60), aadA2/strA/strB], sulfamethoxazole (Sul) [62% (n = 37/60), sul1/sul2/sul3] and ampicillin (A) [57% (n = 34/60), blaPSE-1/blaTEM]. Thirty-seven percent (n = 22/60) carried class 1 integrons and multidrug resistance was frequently observed (63% n = 38/60), including those serotypes common to human infections [S. Typhimurium 78% n = 25/32; S. 4,[5],12:i:- 67% n = 2/3; S. Rissen 75% (n = 3/4); S. London 67% n = 2/3; S. Derby 55%; n = 6/11)]. The emergent S. 4,[5],12:i:- isolates were mostly characterized by ASSuT phenotype [blaTEM/strA-strB/sul2/tet(B)], typical of the European clone, while for the first time the ST phenotype [strA-strB-tet(A)-tet(B)] was also observed. Moreover, we report a first finding of a MDR phenotype in S. London [ANSSuT; blaTEM-strA-strB-sul2-tet(A)]. Our findings suggest that the abattoir environment and the slaughter operations seem not only to harbor MDR serotypes that originated in the pig reservoir, but also propagate them through cross-contamination processes, involving meat handlers. The present study suggests a probable relationship between swine and human salmonellosis throughout the food chain, which is of interest for epidemiological, animal health and public health purposes.