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...

An improved medium for the direct, positive selection of tetracycline-sensitive clones from a population of tetracycline-resistant strains of Escherichia coli is described. Various genetic techniques have been developed requiring the excision of the tetracyclineresistant transposon TnlO from an insertion site

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The proline utilization (put) operon of Salmonella typhimurium is transcriptionally repressed by PutA

Enteric bacteria possess multiple fimbriae, many of which play critical roles in attachment to epithelial cell surfaces. SEF14 fimbriae are only found in Salmonella enterica serovar Enteritidis (S. enteritidis) and closely related serovars, suggesting that SEF14 fimbriae may affect serovar-specific virulence traits. Despite evidence that SEF14 fimbriae are expressed by S. enteritidis in vivo, previous studies showed that SEF14 fimbriae do not mediate adhesion to the intestinal epithelium. Therefore, we tested whether SEF14 fimbriae are required for virulence at a stage in infection after the bacteria have passed the intestinal barrier. Polar mutations that disrupt the entire sef operon decreased virulence in mice more than 1,000-fold. Nonpolar mutations that disrupted sefA (encoding the major structural subunit) did not affect virulence, but mutations that disrupted sefD (encoding the putative adhesion subunit) resulted in a severe virulence defect. The results indicate that the putative SEF14 adhesion subunit is specifically required for a stage of the infection subsequent to transit across the intestinal barrier. Therefore, we tested whether SefD is required for uptake or survival in macrophages. The majority of wild-type bacteria were detected inside macrophages soon after i.p. infection, but the sefD mutants were not readily internalized by peritoneal macrophages. These results indicate that the potential SEF14 adhesion subunit is essential for efficient uptake or survival of S. enteritidis in macrophages. This report describes a role of fimbriae in intracellular infection, and indicates that fimbriae may be required for systemic infections at stages beyond the initial colonization of host epithelial surfaces.