Emergence, distribution, and molecular and phenotypic characteristics of Salmonella enterica serotype 4,5,12:i:-

Abstract

Salmonella spp. represent one of the most common causes of bacterial foodborne illnesses around the world. The species Salmonella enterica contains more than 2500 serotypes, and emergence of new human pathogenic Salmonella strains and serotypes represents a major public health issue. Salmonella enterica subsp. enterica serotype 4,5,12:i:- represents a monophasic variant of Salmonella Typhimurium, which has rarely been identified before the mid-1990 s. The prevalence of this serotype among human salmonellosis cases has increased considerably since the mid-1990 s and Salmonella 4,5,12:i:- currently (i.e., the first decade of the 2000s) represents one of the most common serotypes among human cases in many countries around the world. This paper discusses our current knowledge of the global ecology, epidemiology, transmission, and evolution of this emerging Salmonella serotype.

FIG. 1.

Flagellar phase variation in Salmonella (this figure is reproduced, with permission, from Aldridge et al. [2006]). The reversible, Hin-mediated inversion of the H segment (located between hixL and hixR) results in the inversion of a promoter driving the expression of fljB (which encodes the phase 2 flagellin) and fljA. fljA encodes an inhibitor of fliC, which in turn encodes phase 1 flagellin. The Hin recombinase in conjunction with the Fis protein catalyzes a site-specific recombination reaction between the hixL and hixR recombination sites. The upper part of this figure shows the promoter configuration during phase 2 flagella expression; fljBA is transcribed allowing for production of FljB and FljA, which inhibits fliC transcription. The bottom part of this figure shows the promoter configuration during phase 1 flagella expression; the promoter for fljBA is inverted and thus cannot facilitate fljAB transcription; fliC is transcribed because FljA is not produced and thus cannot inhibit fliC transcription.