Salmonella enterica Serovar Typhi Possesses a Unique Repertoire of Fimbrial Gene Sequences

Abstract

Salmonella enterica serotype Typhi differs from nontyphoidal Salmonella serotypes by its strict host adaptation to humans and higher primates. Since fimbriae have been implicated in host adaptation, we investigated whether the serotype Typhi genome contains fimbrial operons which are unique to this pathogen or restricted to typhoidal Salmonella serotypes. This study established for the first time the total number of fimbrial operons present in an individual Salmonella serotype. The serotype Typhi CT18 genome, which has been sequenced by the Typhi Sequencing Group at the Sanger Centre, contained a type IV fimbrial operon, an orthologue of the agf operon, and 12 putative fimbrial operons of the chaperone-usher assembly class. In addition to sef, fim, saf, and tcf, which had been described previously in serotype Typhi, we identified eight new putative chaperoneusher-dependent fimbrial operons, which were termed bcf, sta, stb, ste, std, stc, stg, and sth. Hybridization analysis performed with 16 strains of Salmonella reference collection C and 22 strains of Salmonella reference collection B showed that all eight putative fimbrial operons of serotype Typhi were also present in a number of nontyphoidal Salmonella serotypes. Thus, a simple correlation between host range and the presence of a single fimbrial operon seems at present unlikely. However, the serotype Typhi genome differed from that of all other Salmonella serotypes investigated in that it contained a unique combination of putative fimbrial operons.The genus Salmonella contains pathogens which are closely related genetically but differ in their host range (7). One end of the spectrum is formed by broad-host-range pathogens such as Salmonella enterica serotype Typhimurium, which is frequently associated with cases of disease in a number of animal species, including mice, pigs, poultry, horses, cattle, and sheep (19,43,52). At the other end of the spectrum are pathogens whose ability to cause disease is restricted to a single genus or related genera of vertebrate species. Serotype Typhi is a prototypical host-restricted serotype which causes typhoid fever in humans and higher primates but is unable to produce illness in other vertebrate species. Since there is no inexpensive animal model with which to study serotype Typhi pathogenesis, little is known about virulence factors which are responsible for its apparent adaptation to the human host and its ability to cause typhoid fever. With the sequence of the whole serotype Typhi genome now almost complete, we can begin to address these questions using comparative genomic analysis.One of the virulence factors recently implicated in adaptation of serotype Typhi to the human host is a fimbrial operon termed tcf, for Typhi colonization factor. Serotype Typhi is the only serotype within Salmonella reference collection C (SARC), a strain collection consisting of 16 isolates representing all phylogenetic lineages within the genus Salmonella, which hybridizes with a DNA probe specific to the tcf operon (20). The serotype...

Genome sequence of Yersinia pestis, the causative agent of plague

“…In ®ve cases the operons are¯anked by genes encoding transposases or integrases, again implying horizontal acquisition. Such high redundancy of ®mbria-related genes is also found in other bacterial pathogens, including Escherichia coli and Salmonella enterica serovar Typhi 17 . A large arsenal of independent gene clusters encoding different ®mbriae and adhesins might be bene®cial in evading host immune response, or may allow multiple interactions with several different hosts during its complex life cycle.…”

The broad host range pathogen Pseudomonas aeruginosa strain PA14 carries two pathogenicity islands harboring plant and animal virulence genes

“…2 and Tables 2 and 4). Moreover, 21 additional PAPI-1 ORFs show similarity with ORFs from only one of these pathogenicity islands, 14 with S. enterica (RL052, 72, 77-79, 81-85) and 7 with X. axonopodis (RL020, 35,[63][64][65]67). This abundant array of putative pathogenicity-related genes likely plays a role in the broad host range of PA14.…”

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. Early hypotheses that fimbriae were involved in adherence to host cells suggested that numerous fimbrial types would contribute to the host specificities and tissue tropisms of different Salmonella spp.…”

“…However, despite much research, the role of fimbriae in the pathogenesis of Salmonella is still not well understood. In addition, no clear links have been made connecting one fimbrial type to a particular animal host or disease process (61).…”