Salmonella: clinical importance and evolution of nomenclature.

Salmonella is an important pathogen for both humans and animals. Although the organism has been intensively studied during the last century, much remains to be learned about this pathogen. The complicated nomenclature system of Salmonella has long been a subject of discussion. In 2005, "Salmonella enterica" finally gained official approval as the type species of the genus Salmonella. The genus Salmonella also contains the species "Salmonella bongori" in addition to a new species, "Salmonella subterranean", which was recognized in 2005. Unlike other bacterial genera, Salmonella organisms are differentiated by serotyping analysis. Presently, new serotypes (serovars) are still being discovered each year, adding to the complexity of this large bacterial population. Despite the conserved genetic background, molecular analysis has indicated successful evolution of the Salmonella genome in response to the environment, particularly to the selective pressure from antimicrobial agents. Mechanisms of fluoroquinolone resistance in Salmonella are similar to the complex system reported for other members of the family Enterobacteriaceae. On the other hand, resistance to extended-spectrum cephalosporins is more likely to be mediated by bla(CTX-M) or ampC genes that are carried on plasmids. Plasmid-borne genes have increased efficacy in the dissemination of resistance determinants, resulting in increased antimicrobial resistance. To provide clinicians with up-to-date information on this important pathogen, the evolving nomenclature and clinical importance of Salmonella are reviewed.