Comparison of genome degradation in Paratyphi A and Typhi, human-restricted serovars of Salmonella enterica that cause typhoid

Abstract

Salmonella enterica serovars often have a broad host range, and some cause both gastrointestinal and systemic disease. But the serovars Paratyphi A and Typhi are restricted to humans and cause only systemic disease. It has been estimated that Typhi arose in the last few thousand years. The sequence and microarray analysis of the Paratyphi A genome indicates that it is similar to the Typhi genome but suggests that it has a more recent evolutionary origin. Both genomes have independently accumulated many pseudogenes among their approximately 4,400 protein coding sequences: 173 in Paratyphi A and approximately 210 in Typhi. The recent convergence of these two similar genomes on a similar phenotype is subtly reflected in their genotypes: only 30 genes are degraded in both serovars. Nevertheless, these 30 genes include three known to be important in gastroenteritis, which does not occur in these serovars, and four for Salmonella-translocated effectors, which are normally secreted into host cells to subvert host functions. Loss of function also occurs by mutation in different genes in the same pathway (e.g., in chemotaxis and in the production of fimbriae).

Salmonella Typhi: from a Human Pathogen to a Vaccine Vector

“…This is in line with other genomes of enteric bacteria sequenced so far which feature a single chromosome with 4.3-5.0 Mb in length (7)(8)(9)(10). A comparison of S. typhi isolates from around the world indicate that they are highly related and that they emerged from a single point of origin approximately 30,000 to 50,000 years ago (11).…”

“…Unlike most other serovars, Salmonella typhi expresses the Vi polysaccharide capsule, an important virulent factor. However, its presence only increases the infectivity of Salmonella typhi and the severity of the disease but is not essential for infection since it has been shown that Vi negative mutants are able to cause a typhoid-like illness in human volunteers (7,31). Supporting this view is the fact that there have been reports of outbreaks of typhoid fever caused by Vi-negative Salmonella typhi (32).…”

Use of multilocus variable-number tandem repeat analysis in molecular subtyping of Salmonella enterica serovar Typhi isolates

“…S. Typhi and S. Paratyphi A are more closely related at the DNA level than other Salmonella serovars, as indicated by whole genome sequence comparisons (McClelland et al, 2004). The genomic sequences of S. Typhi strain CT18 (GenBank accession no.…”

Comparative Genetics of the rdar Morphotype inSalmonella

“…For pathogenic Salmonella spp., genome sequencing efforts have identified over 15 distinct fimbrial types (Salmonella enterica serovars Typhimurium [42], Typhi [44], and Paratyphi [41]). Pioneering work by Baumler et al (5) and subsequent genomic comparisons (14,45,61) revealed that most fimbrial operons have a scattered distribution throughout the salmonellae.…”