In 200 sulfonamide-resistant Portuguese Salmonella isolates, 152 sul1 , 74 sul2 , and 14 sul3 genes were detected. Class 1 integrons were always associated with sul genes, including sul3 alone in some isolates. The sul3 gene has been identified in isolates from different sources and serotypes, which also carried a class 1 integron with aadA and dfrA gene cassettes.

Salmonellosis remains one of the most frequent foodborne zoonosis, constituting a worldwide major public health concern. The most frequent sources of human infections are food products of animal origin, being pork meat one of the most relevant. Currently, particular pig food production well-adapted and persistent Salmonella enterica serotypes (e.g., Salmonella Typhimurium, Salmonella 1,4,[5],12:i:-, Salmonella Derby and Salmonella Rissen) are frequently reported associated with human infections in diverse industrialized countries. The dissemination of those clinically-relevant Salmonella serotypes/clones has been related to the intensification of pig production chain and to an increase in the international trade of pigs and pork meat. Those changes that occurred over the years along the food chain may act as food chain drivers leading to new problems and challenges, compromising the successful control of Salmonella. Among those, the emergence of antibiotic resistance in non-typhoidal Salmonella associated with antimicrobials use in the pig production chain is of special concern for public health. The transmission of pig-related multidrug-resistant Salmonella serotypes, clones and/or genetic elements carrying clinically-relevant antibiotic resistance genes, frequently associated with metal tolerance genes, from pigs and pork meat to humans, has been reported and highlights the contribution of different drivers to the antibiotic resistance burden. Gathered data strengthen the need for global mandatory interventions and strategies for effective Salmonella control and surveillance across the pig production chain. The purpose of this review was to provide an overview of the role of pig and pork meat in human salmonellosis at a global scale, highlighting the main factors contributing to the persistence and dissemination of clinically-relevant pig-related Salmonella serotypes and clones.

The mcr-1 gene was found in 11 isolates from a Portuguese Salmonella collection (n = 1,010; 58 serotypes; 2002–15) of clinical samples, foodstuff, food-animals and water. Mcr-1 has been located on different plasmids (IncX4/IncHI2) in pig-associated multidrug-resistant, copper-tolerant S.1,4,[5],12:i:-/ST34 and S. Rissen/ST469 clones from human and pork products since at least 2011. Our data highlight dissemination of mcr-1 by successful resistant clones in Europe and raise questions about the efficacy of copper-based interventions to reduce colistin use.

A sul3 domain (IS 440 - sul3 - orf1 -IS 26 ) was found linked to an unusual 3′ conserved sequence region ( qacH ) of class 1 integrons and detected among nontyphoid Salmonella isolates ( n = 47) from different sources. Three types of integrons differing in the gene cassette array ( dfrA12 - orfF - aadA2 - cmlA1 - aadA1 , dfrA12 - orfF - aadA2 / 1 , and estX - psp - aadA2 - cmlA1 - aadA1 ) were found associated with this sul3 domain. They were associated with particular clones and specific high-molecular-weight plasmids.