A chromosomal region surrounding the ompD porin gene marks a genetic difference between Salmonella typhi and the majority of Salmonella serovars

Abstract

In this work it is shown that the majority of Salmonella serovars most frequently associated with the systemic infection of vertebrate hosts produce a major outer-membrane porin, OmpD. However, OmpD is absent from the outer-membrane protein profiles of Salmonella typhi strain Ty2 and 26 clinical isolates of S. typhi examined by SDS-PAGE. To determine whether the ompD gene is present in S. typhi, primers internal to the ompD coding sequence were used to amplify the gene by PCR. With the exception of S. typhi strains, the ompD gene was amplified from the genomes of all Salmonella serovars tested. Consistently, a specific ompD probe did not hybridize with DNA isolated from the S. typhi strains. Taken together, these results demonstrate that S. typhi does not produce OmpD due to the absence of the ompD gene. Furthermore, it was investigated whether the deletion of ompD extended to smvA. This gene is adjacent to ompD in the Salmonella typhimurium chromosome and encodes a protein involved in the resistance to methyl viologen, a superoxide-generating agent. Although PCR failed to amplify the smvA gene from the S. typhi strain Ty2 genome, it was possible to amplify it from the chromosome of the clinical strains. On the other hand, hybridization analyses showed that the smvA gene is present in all the S. typhi strains tested. In contrast to the other Salmonella serovars, S. typhi strain Ty2 and the clinical isolates showed sensitivity to methyl viologen, suggesting that smvA gene is inactive in S. typhi. In conclusion, the ompD-smvA region is variable in structure among Salmonella serovars. It is hypothesized that the absence of ompD may suggest a role in host specificity.

Differences in Gene Content among Salmonella enterica Serovar Typhi Isolates

“…Third, the gene cluster of STM1568 to STM1572 encoding nitrate inducible formate dehydrogenase subunits (fdnIH), a molybdopterin-dependent oxidoreductase (fdnG), a permease (yddG), and a predicted porin (nmpC or ompD) have homologues in both SARB63 and SARB64 but in none of the other Typhi isolates. Previous observations had suggested the absence of ompD from all clinical Typhi isolates (24).…”

Global Regulation of the Salmonella enterica Serovar Typhimurium Major Porin, OmpD

“…This region, which maps at minute 33.7 on the serovar Typhimurium chromosome, includes two adjacent genes, ompD and yddG, which are not present on the serovar Typhi genome (21,22). The ompD gene encodes the most abundant protein in the outer membrane, a porin similar in primary amino acid sequence to the major porins OmpC, OmpF, and PhoE.…”

“…As a complementary approach to understand the function of ompD, we constructed a serovar Typhi hybrid carrying the serovar Typhimurium ompD gene. This serovar Typhi hybrid expresses the OmpD porin in its outer membrane and has a gain-offunction phenotype, increased resistance to methyl viologen (21,22).…”

Precise Excision of the Large Pathogenicity Island, SPI7, inSalmonella entericaSerovar Typhi

“…S. enterica serovar Typhi clinical strains are from the Infection Disease Hospital Lucio Cordova in Santiago, Chile, and have been described previously (55). Each strain was isolated directly from blood samples of different patients being treated for typhoid fever.…”

“…Standard conditions for amplification were 30 cycles of incubation at 96°C for 40 s, 60°C for 40 s, and 72°C for 3 min, followed by a final extension step at 72°C for 10 min. Template S. enterica serovar Typhi chromosomal DNA was prepared as described previously (55), and the sequences of the primers used are listed in Table 1. Sequencing of the amplified PCR products from SARB50, STH2327, Ty2, and STH2370⌬SPI7 genomic DNA templates across SPI7 deletion join points was performed by the Center of DNA and Peptide Sequencing at Pontificia Universidad Católica de Chile.…”