TheshdAGene Is Restricted to Serotypes ofSalmonella entericaSubspecies I and Contributes to Efficient and Prolonged Fecal Shedding

Abstract

Little is known about factors which enable Salmonella serotypes to circulate within populations of livestock and domestic fowl. We have identified a DNA region which is present in Salmonella serotypes commonly isolated from livestock and domestic fowl (S. enterica subspecies I) but absent from reptile-associated Salmonella serotypes (S. bongori and S. enterica subspecies II to VII). This DNA region was cloned from Salmonella serotype Typhimurium and sequence analysis revealed the presence of a 6,105-bp open reading frame, designated shdA, whose product's deduced amino acid sequence displayed homology to that of AIDA-I from diarrheagenic Escherichia coli, MisL of serotype Typhimurium, and IcsA of Shigella flexneri. The shdA gene was located adjacent to xseA at 52 min, in a 30-kb DNA region which is not present in Escherichia coli K-12. A serotype Typhimurium shdA mutant was shed with the feces in reduced numbers and for a shorter period of time compared to its isogenic parent. A possible role for the shdA gene during the expansion in host range of S. enterica subspecies I to include warm-blooded vertebrates is discussed.Salmonella serotypes are a frequent constituent of the intestinal flora of poikilothermic animals. The percentage of apparently healthy, cold-blooded vertebrates which harbor Salmonella serotypes ranges from 74 to 94% (20,28,32,34,59), and these bacteria could thus be considered part of the normal intestinal flora (23,48). Salmonella serotypes are also commonly isolated from a fraction (usually Ͻ20%) of warmblooded animal hosts (15,31,49,54). Although chronic carriers, which appear healthy, are observed within the human population and among warm-blooded animals (22,27,35,40), Salmonella serotypes are commonly associated with illness in these hosts (55). Consequently Salmonella serotypes are regarded as pathogens rather than part of the normal intestinal flora of homeothermic animals.On the basis of multilocus enzyme electrophoresis and comparative sequence analysis of orthologous genes, two species, S. enterica and S. bongori, have been assigned to the genus Salmonella (18,46). S. enterica is further subdivided into seven subspecies designated with roman numerals (18, 44). While S. bongori and S. enterica subspecies II, IIIa, IIIb, IV, VI, and VII are mainly associated with cold-blooded vertebrates, members of S. enterica subspecies I are frequently isolated from avian and mammalian hosts (44). For instance, of the 90,201 Salmonella isolates collected between 1977 and 1992 by the German National Reference Center for Enteric Pathogens from humans and warm-blooded animals, 89,798 isolates (99.55%) belonged to S. enterica subspecies I (1). Currently it is not clear which virulence mechanisms are responsible for the apparent adaptation of S. enterica subspecies I to circulation within populations of warm-blooded animals.S. bongori or S. enterica subspecies II to VII are able to infect humans, colonize the intestine and cause disease (1). Human infections with serotypes of S. bongori and S. enterica su...

Protein expression diversity amongst serovars of Salmonella enterica

“…manifest different disease symptoms. Such differences in the capacity to spread and adapt to different conditions can be observed amongst the serovars of Salmonella enterica subspecies enterica (Kingsley et al, 2000;Kingsley & Baümler, 2002). The existence of host-generalist and host-adapted variants of this species provides a unique opportunity to study the mechanisms defining the process of host adaptation, not only at the level of DNA sequences, but also at the level of the expressed proteome, which could reveal modifications and expression-level differences not detectable from the DNA data.…”

Evolutionary genomics of Salmonella : Gene acquisitions revealed by microarray analysis

“…The ssp. 1 salmonellae also may have added the envF gene at this stage, encoding an envelope lipoprotein, and the shdA gene, a Peyer's patch colonization and shedding factor (33). Cluster STM 3251-3256 encodes components of sugar activation and transport (fructose-specific phosphotransferase system component IIA and putative sugar kinases), specific for ssp.…”

Vancomycin-resistant Enterococcus domination of intestinal microbiota is enabled by antibiotic treatment in mice and precedes bloodstream invasion in humans

“…Our finding that mice that recovered from antibiotic treatment were more susceptible to VRE colonization is consistent with this hypothesis. Similar to VRE, other bacteria, such as Salmonella, persist in the intestine for long periods of time (42). Moreover, as with VRE, mice that recover from antibiotic treatment are more susceptible to Salmonella intestinal colonization (30).…”