from Indrani Karunasagar, Patit Paban Bhowmick and Deekshit Vijaya Kumar writing in Foodborne and Waterborne Bacterial Pathogens: Epidemiology, Evolution and Molecular Biology:
Foodborne and waterborne infections due to Salmonella species are a major concern worldwide. Several virulence genes have been identified in Salmonella and located in clusters called Salmonella Pathogenicity Island (SPI). There are 17 Pathogenicity Islands of Salmonella reported to date. Salmonella possess two distinct type three secretion system (T3SS) encoded by genes present in two different SPI viz. SPI-1 and SPI-2 that play an important role in adhesion, invasion and survival in the host cells. It has been also reported that a variety of Salmonella phenotypes associated with bioluminescence, biofilm formation, conjugation, motility, competence, and antibiotic production, are regulated in response to signaling molecules of quorum-sensing systems. The development of resistance to various antibiotics (particularly in Asian countries) including extended-spectrum cephalosporins worldwide is a cause of concern. Some variants of Salmonella have developed multidrug-resistance as an integral part of the genetic material of the organism, and are therefore likely to retain their drug-resistance genes even when antimicrobial drugs are no longer used. The role of plasmids, bacteriophages, transposons and integrons in the transfer of resistance genes is discussed.
Further reading: Foodborne and Waterborne Bacterial Pathogens: Epidemiology, Evolution and Molecular Biology