Dataset Information

Recombinational basis of serovar diversity in Salmonella enterica.

ABSTRACT: The fliC gene, which encodes phase 1 flagellin, was sequenced in strains of 15 Salmonella enterica serovars expressing flagellar antigenic factors of the g series. The occurrence of each of the flagellin serotypes g,m, m,t, and g,z51 in distantly related strains is the result of horizontal exchange of DNA, as indicated by identity or close similarity in nucleotide sequence of all or parts of the antigenic factor-determining central region of fliC. The flagellin genes of some serovars are complex mosaic structures composed of diverse segments derived through multiple recombination events. Thus, recombination of horizontally transferred segments (intragenic) or entire genes (assortative) within and among subspecies is identified as a major evolutionary mechanism generating both allelic variation at the fliC locus and serovar diversity in natural populations. Evidence that flagellar serological diversity is promoted by diversifying selection in adaptation to host immune defense system or flagellotropic phage is discussed.

SUBMITTER: Li J

PROVIDER: S-EPMC43407 | biostudies-other | 1994 Mar

REPOSITORIES: biostudies-other

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Recombinational basis of serovar diversity in Salmonella enterica.

Li J J Nelson K K McWhorter A C AC Whittam T S TS Selander R K RK

Proceedings of the National Academy of Sciences of the United States of America 19940301 7

The fliC gene, which encodes phase 1 flagellin, was sequenced in strains of 15 Salmonella enterica serovars expressing flagellar antigenic factors of the g series. The occurrence of each of the flagellin serotypes g,m, m,t, and g,z51 in distantly related strains is the result of horizontal exchange of DNA, as indicated by identity or close similarity in nucleotide sequence of all or parts of the antigenic factor-determining central region of fliC. The flagellin genes of some serovars are complex ...[more]

PMID: 8146152

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Project description:Salmonella enterica serovar Enteritidis has emerged as a significant foodborne pathogen throughout the world and is commonly characterized by phage typing. In Canada phage types (PT) 4, 8 and 13 predominate and in 2005 a large foodborne PT13 outbreak occurred in the province of Ontario. The ability to link strains during this outbreak was difficult due to the apparent clonality of PT13 isolates in Canada, as there was a single dominant pulsed-field gel electrophoresis (PFGE) profile amongst epidemiologically linked human and food isolates as well as concurrent sporadic strains. The aim of this study was to perform comparative genomic hybridization (CGH), DNA sequence-based typing (SBT) genomic analyses, plasmid analyses, and automated repetitive sequence-based PCR (rep-PCR) to identify epidemiologically significant traits capable of subtyping S. Enteritidis PT13.CGH using an oligonucleotide array based upon chromosomal coding sequences of S. enterica serovar Typhimurium strain LT2 and the Salmonella genomic island 1 successfully determined major genetic differences between S. Typhimurium and S. Enteritidis PT13, but no significant strain-to-strain differences were observed between S. Enteritidis PT13 isolates. Individual loci (safA and fliC) that were identified as potentially divergent in the CGH data set were sequenced in a panel of S. Enteritidis strains, and no differences were detected between the PT13 strains. Additional sequence-based typing was performed at the fimA, mdh, manB, cyaA, citT, caiC, dmsA, ratA and STM0660 loci. Similarly, no diversity was observed amongst PT13 strains. Variation in plasmid content between PT13 strains was observed, but macrorestriction with BglII did not identify further differences. Automated rep-PCR patterns were variable between serovars, but S. Enteritidis PT13 strains could not be differentiated.None of the methods identified any significant variation between PT13 strains. Greater than 11,300 base pairs of sequence for each of seven S. Enteritidis PT13 strains were analyzed without detecting a single polymorphic site, although diversity between different phage types of S. Enteritidis was observed. These data suggest that Canadian S. Enteritidis PT13 strains are highly related genetically.

Project description:BackgroundTyphoid fever is an acute systemic infection of humans caused by Salmonella enterica subspecies enterica serovar Typhi (S. Typhi). In chronic carriers, the bacteria survive the harsh environment of the gallbladder by producing biofilm. The phenotype of S. Typhi biofilm cells is significantly different from the free-swimming planktonic cells, and studies have shown that they are associated with antibiotic resistance, immune system evasion, and bacterial persistence. However, the mechanism of this transition and the events leading to biofilm formation are unknown. High throughput sequencing was performed to identify the genes involved in biofilm formation and to postulate the mechanism of action.ResultsPlanktonic S. Typhi cells were cultured using standard nutrient broth whereas biofilm cells were cultured in a stressful environment using high shearing-force and bile to mimic the gallbladder. Sequencing libraries were prepared from S. Typhi planktonic cells and mature biofilm cells using the Illumina HiSeq 2500 platform, and the transcriptome data obtained were processed using Cufflinks bioinformatics suite of programs to investigate differential gene expression between the two phenotypes. A total of 35 up-regulated and 29 down-regulated genes were identified. The identities of the differentially expressed genes were confirmed using NCBI BLAST and their functions were analyzed. The results showed that the genes associated with metabolic processes and biofilm regulations were down-regulated while those associated with the membrane matrix and antibiotic resistance were highly up-regulated.ConclusionsIt is proposed that the biofilm phenotype of S. Typhi allows the bacteria to increase production of the membrane matrix in order to serve as a physical shield and to adhere to surfaces, and enter an energy conservation state in response to the stressful environment. Conversely, the planktonic phenotype allows the bacteria to produce flagella and increase metabolic activity to enable the bacteria to migrate and form new colonies of infection. This data provide a basis for further studies to uncover the mechanism of biofilm formation in S. Typhi and to discover novel genes or pathways associated with the development of the typhoid carrier state.

Dataset Information

Recombinational basis of serovar diversity in Salmonella enterica.

Publications

Recombinational basis of serovar diversity in Salmonella enterica.

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