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Evolution of Salmonella enterica virulence via point mutations in the fimbrial adhesin.

Kisiela DI, Chattopadhyay S, Libby SJ, Karlinsey JE, Fang FC, Tchesnokova V, Kramer JJ, Beskhlebnaya V, Samadpour M, Grzymajlo K, Ugorski M, Lankau EW, Mackie RI, Clegg S, Sokurenko EV - PLoS Pathog. (2012)

Bottom Line: We have found that while the low-binding shear-dependent phenotype of the adhesin is preserved in broad host-range (usually systemically non-invasive) Salmonella, the majority of host-adapted serovars express FimH variants with one of two alternative phenotypes: a significantly increased binding to mannose (as in S.The functional diversification of FimH in host-adapted Salmonella results from recently acquired structural mutations.In conclusion, our study demonstrates that point mutations are the target of positive selection and, in addition to horizontal gene transfer and genome degradation events, can contribute to the differential pathoadaptive evolution of Salmonella.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
Whereas the majority of pathogenic Salmonella serovars are capable of infecting many different animal species, typically producing a self-limited gastroenteritis, serovars with narrow host-specificity exhibit increased virulence and their infections frequently result in fatal systemic diseases. In our study, a genetic and functional analysis of the mannose-specific type 1 fimbrial adhesin FimH from a variety of serovars of Salmonella enterica revealed that specific mutant variants of FimH are common in host-adapted (systemically invasive) serovars. We have found that while the low-binding shear-dependent phenotype of the adhesin is preserved in broad host-range (usually systemically non-invasive) Salmonella, the majority of host-adapted serovars express FimH variants with one of two alternative phenotypes: a significantly increased binding to mannose (as in S. Typhi, S. Paratyphi C, S. Dublin and some isolates of S. Choleraesuis), or complete loss of the mannose-binding activity (as in S. Paratyphi B, S. Choleraesuis and S. Gallinarum). The functional diversification of FimH in host-adapted Salmonella results from recently acquired structural mutations. Many of the mutations are of a convergent nature indicative of strong positive selection. The high-binding phenotype of FimH that leads to increased bacterial adhesiveness to and invasiveness of epithelial cells and macrophages usually precedes acquisition of the non-binding phenotype. Collectively these observations suggest that activation or inactivation of mannose-specific adhesive properties in different systemically invasive serovars of Salmonella reflects their dynamic trajectories of adaptation to a life style in specific hosts. In conclusion, our study demonstrates that point mutations are the target of positive selection and, in addition to horizontal gene transfer and genome degradation events, can contribute to the differential pathoadaptive evolution of Salmonella.

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FimH-mediated bacterial interaction with epithelial and macrophage cell lines.Bacterial adhesion to (A and C) and invasion of (B and D) Hep-2 cells (A and B) and RAW264.7 cells (C and D). Different variants of FimH were expressed in S. Typhimurium SL1344H3 and bacterial binding was tested in the absence and presence of 50 mM methyl-D-mannopyranoside (α-mm). Data are the means ± SD of triplicates from one representative experiment of three experiments that were performed.
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ppat-1002733-g006: FimH-mediated bacterial interaction with epithelial and macrophage cell lines.Bacterial adhesion to (A and C) and invasion of (B and D) Hep-2 cells (A and B) and RAW264.7 cells (C and D). Different variants of FimH were expressed in S. Typhimurium SL1344H3 and bacterial binding was tested in the absence and presence of 50 mM methyl-D-mannopyranoside (α-mm). Data are the means ± SD of triplicates from one representative experiment of three experiments that were performed.

Mentions: We investigated how variation in mannose-binding by Salmonella FimH affects bacterial cell adhesion and invasion. The human epithelial cell line HEp-2 and the murine macrophage cell line RAW264.7 were used as target cells. We compared isogenic strains that express two previously characterized S. Typhimurium FimH variants, low-binding FimHSL1344 (Thm1) and high-binding FimHAJB3 (Thm3), that differ in a single amino acid N136Y, and FimH variants from five other serovars: Enteritidis (Ent1, low-binding), Dublin (Dub1, medium-binding), Choleraesuis strain Chl5 and Typhi strain Typ1 (both high-binding), and Choleraesuis strain Chl1 (non-binding). Bacterial adhesion and invasion were assessed after allowing a bacterial suspension to interact with the target cell monolayers under static conditions without centrifugation. As shown in Figure 6, the level of bacterial binding to both epithelial cells (6A) and macrophages (6C) corresponded well to the mannose-binding capability of the FimH variants, with the high-binding FimH mediating up to 10-fold higher adhesion than the low-binding variants and up to 100-fold higher adhesion than inactive FimH of Choleraesuis (Chl1) or the FimH knockout strain that does not express type 1 fimbriae (fimHΔ). The binding was strongly inhibited by a soluble mannose derivative (methyl-alpha-D-mannopyranoside). Thus, under our experimental conditions cell adhesion is primarily mediated by FimH, and the variants with activating mutations mediate significantly better cell binding. When bacterial internalization was assessed (Figure 6B and D), the pattern generally was the same. Consequently, the highly-adhering bacteria were internalized to a significantly higher degree than the low-adhering bacteria. However, while the level of FimH-dependent bacterial adhesion to these two types of eukaryotic cells was similar, the invasion level differed significantly with 75 times greater invasion of the macrophage cell line (7.4–13.2% of bacterial inoculum) compared to the epithelial cells (0.07–0.19% of bacterial inoculum). Again, invasion was strongly inhibited by soluble mannose.


Evolution of Salmonella enterica virulence via point mutations in the fimbrial adhesin.

Kisiela DI, Chattopadhyay S, Libby SJ, Karlinsey JE, Fang FC, Tchesnokova V, Kramer JJ, Beskhlebnaya V, Samadpour M, Grzymajlo K, Ugorski M, Lankau EW, Mackie RI, Clegg S, Sokurenko EV - PLoS Pathog. (2012)

FimH-mediated bacterial interaction with epithelial and macrophage cell lines.Bacterial adhesion to (A and C) and invasion of (B and D) Hep-2 cells (A and B) and RAW264.7 cells (C and D). Different variants of FimH were expressed in S. Typhimurium SL1344H3 and bacterial binding was tested in the absence and presence of 50 mM methyl-D-mannopyranoside (α-mm). Data are the means ± SD of triplicates from one representative experiment of three experiments that were performed.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3369946&req=5

ppat-1002733-g006: FimH-mediated bacterial interaction with epithelial and macrophage cell lines.Bacterial adhesion to (A and C) and invasion of (B and D) Hep-2 cells (A and B) and RAW264.7 cells (C and D). Different variants of FimH were expressed in S. Typhimurium SL1344H3 and bacterial binding was tested in the absence and presence of 50 mM methyl-D-mannopyranoside (α-mm). Data are the means ± SD of triplicates from one representative experiment of three experiments that were performed.
Mentions: We investigated how variation in mannose-binding by Salmonella FimH affects bacterial cell adhesion and invasion. The human epithelial cell line HEp-2 and the murine macrophage cell line RAW264.7 were used as target cells. We compared isogenic strains that express two previously characterized S. Typhimurium FimH variants, low-binding FimHSL1344 (Thm1) and high-binding FimHAJB3 (Thm3), that differ in a single amino acid N136Y, and FimH variants from five other serovars: Enteritidis (Ent1, low-binding), Dublin (Dub1, medium-binding), Choleraesuis strain Chl5 and Typhi strain Typ1 (both high-binding), and Choleraesuis strain Chl1 (non-binding). Bacterial adhesion and invasion were assessed after allowing a bacterial suspension to interact with the target cell monolayers under static conditions without centrifugation. As shown in Figure 6, the level of bacterial binding to both epithelial cells (6A) and macrophages (6C) corresponded well to the mannose-binding capability of the FimH variants, with the high-binding FimH mediating up to 10-fold higher adhesion than the low-binding variants and up to 100-fold higher adhesion than inactive FimH of Choleraesuis (Chl1) or the FimH knockout strain that does not express type 1 fimbriae (fimHΔ). The binding was strongly inhibited by a soluble mannose derivative (methyl-alpha-D-mannopyranoside). Thus, under our experimental conditions cell adhesion is primarily mediated by FimH, and the variants with activating mutations mediate significantly better cell binding. When bacterial internalization was assessed (Figure 6B and D), the pattern generally was the same. Consequently, the highly-adhering bacteria were internalized to a significantly higher degree than the low-adhering bacteria. However, while the level of FimH-dependent bacterial adhesion to these two types of eukaryotic cells was similar, the invasion level differed significantly with 75 times greater invasion of the macrophage cell line (7.4–13.2% of bacterial inoculum) compared to the epithelial cells (0.07–0.19% of bacterial inoculum). Again, invasion was strongly inhibited by soluble mannose.

Bottom Line: We have found that while the low-binding shear-dependent phenotype of the adhesin is preserved in broad host-range (usually systemically non-invasive) Salmonella, the majority of host-adapted serovars express FimH variants with one of two alternative phenotypes: a significantly increased binding to mannose (as in S.The functional diversification of FimH in host-adapted Salmonella results from recently acquired structural mutations.In conclusion, our study demonstrates that point mutations are the target of positive selection and, in addition to horizontal gene transfer and genome degradation events, can contribute to the differential pathoadaptive evolution of Salmonella.

View Article: PubMed Central - PubMed

Affiliation: Department of Microbiology, University of Washington, Seattle, Washington, United States of America.

ABSTRACT
Whereas the majority of pathogenic Salmonella serovars are capable of infecting many different animal species, typically producing a self-limited gastroenteritis, serovars with narrow host-specificity exhibit increased virulence and their infections frequently result in fatal systemic diseases. In our study, a genetic and functional analysis of the mannose-specific type 1 fimbrial adhesin FimH from a variety of serovars of Salmonella enterica revealed that specific mutant variants of FimH are common in host-adapted (systemically invasive) serovars. We have found that while the low-binding shear-dependent phenotype of the adhesin is preserved in broad host-range (usually systemically non-invasive) Salmonella, the majority of host-adapted serovars express FimH variants with one of two alternative phenotypes: a significantly increased binding to mannose (as in S. Typhi, S. Paratyphi C, S. Dublin and some isolates of S. Choleraesuis), or complete loss of the mannose-binding activity (as in S. Paratyphi B, S. Choleraesuis and S. Gallinarum). The functional diversification of FimH in host-adapted Salmonella results from recently acquired structural mutations. Many of the mutations are of a convergent nature indicative of strong positive selection. The high-binding phenotype of FimH that leads to increased bacterial adhesiveness to and invasiveness of epithelial cells and macrophages usually precedes acquisition of the non-binding phenotype. Collectively these observations suggest that activation or inactivation of mannose-specific adhesive properties in different systemically invasive serovars of Salmonella reflects their dynamic trajectories of adaptation to a life style in specific hosts. In conclusion, our study demonstrates that point mutations are the target of positive selection and, in addition to horizontal gene transfer and genome degradation events, can contribute to the differential pathoadaptive evolution of Salmonella.

Show MeSH
Related in: MedlinePlus