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Vibrio cholerae CsrA Regulates ToxR Levels in Response to Amino Acids and Is Essential for Virulence.

Mey AR, Butz HA, Payne SM - MBio (2015)

Bottom Line: Conversely, specific amino acid substitutions in CsrA were associated with defects in ToxR production in response to NRES.Unlike previously described effects of CsrA on virulence gene regulation, the effects of CsrA on ToxR were not mediated through quorum sensing and HapR.By linking environmental sensing to the ToxR regulon, CsrA effectively acts as a switch that controls pathogenesis in response to specific signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biosciences and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, USA armey@austin.utexas.edu.

No MeSH data available.


Related in: MedlinePlus

CsrA is required for V. cholerae virulence in infant mice. The CsrA Arg6His point mutant NcsrA.R6H was competed against the wild-type strain N16961G. Five-day-old suckling BALB/c mice were inoculated intragastrically with an equal number of each competing strain as described in Materials and Methods. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. Each data point represents one mouse, and the median CI (0.01) is represented by the solid horizontal line. A CI value below 1 indicates that the mutant is at a competitive disadvantage. The dotted line shows the limit of detection for the CI in this experiment, which was 0.005. In 4 out of 9 mice, the mutant was not detected during analysis of more than 200 recovered colonies, and thus the CI falls below the limit of detection. These data points are included in the analysis as having a value of 0.005, which is the most conservative estimate for the CI. The actual CI values are likely to be lower. The results were statistically significant (P < 0.05) by the Mann-Whitney nonparametric test.
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fig8: CsrA is required for V. cholerae virulence in infant mice. The CsrA Arg6His point mutant NcsrA.R6H was competed against the wild-type strain N16961G. Five-day-old suckling BALB/c mice were inoculated intragastrically with an equal number of each competing strain as described in Materials and Methods. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. Each data point represents one mouse, and the median CI (0.01) is represented by the solid horizontal line. A CI value below 1 indicates that the mutant is at a competitive disadvantage. The dotted line shows the limit of detection for the CI in this experiment, which was 0.005. In 4 out of 9 mice, the mutant was not detected during analysis of more than 200 recovered colonies, and thus the CI falls below the limit of detection. These data points are included in the analysis as having a value of 0.005, which is the most conservative estimate for the CI. The actual CI values are likely to be lower. The results were statistically significant (P < 0.05) by the Mann-Whitney nonparametric test.

Mentions: ToxR is a critical virulence factor within the mammalian host (4, 33, 34), suggesting that functional CsrA may also be necessary for the pathogenesis of V. cholerae. To test this, we assessed the ability of the NcsrA.R6H mutant to colonize infant mice. The infant mouse model has been shown to be effective in demonstrating the importance of many major virulence factors in this pathogen (35). A competition assay was performed to compare the in vivo fitness of the NcsrA.R6H point mutant to that of the wild-type strain. As described earlier, the NcsrA.R6H strain was not impaired in its in vitro growth but failed to increase ToxR and OmpU levels in response to the NRES mix. Five-day-old infant mice were inoculated intragastrically with equal numbers of the wild-type strain and the NcsrA.R6H mutant. The ability of the mutant strain to compete with the wild-type strain was assessed by determining the ratio of viable mutant cells to wild-type cells recovered after 18 h. The median competitive index (CI [i.e., the output ratio normalized to the input ratio]) for the NcsrA.R6H mutant was <0.01, showing a severe defect in the ability to colonize the infant mouse (Fig. 8). Four of the nine animals yielded results that were below the limit of detection (CI, <0.005), and therefore the median CI is likely even lower than what was computed. These data point to an overall decrease in fitness of more than 100-fold for the mutant strain, showing that CsrA is critical for colonization of the small intestine.


Vibrio cholerae CsrA Regulates ToxR Levels in Response to Amino Acids and Is Essential for Virulence.

Mey AR, Butz HA, Payne SM - MBio (2015)

CsrA is required for V. cholerae virulence in infant mice. The CsrA Arg6His point mutant NcsrA.R6H was competed against the wild-type strain N16961G. Five-day-old suckling BALB/c mice were inoculated intragastrically with an equal number of each competing strain as described in Materials and Methods. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. Each data point represents one mouse, and the median CI (0.01) is represented by the solid horizontal line. A CI value below 1 indicates that the mutant is at a competitive disadvantage. The dotted line shows the limit of detection for the CI in this experiment, which was 0.005. In 4 out of 9 mice, the mutant was not detected during analysis of more than 200 recovered colonies, and thus the CI falls below the limit of detection. These data points are included in the analysis as having a value of 0.005, which is the most conservative estimate for the CI. The actual CI values are likely to be lower. The results were statistically significant (P < 0.05) by the Mann-Whitney nonparametric test.
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Related In: Results  -  Collection

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fig8: CsrA is required for V. cholerae virulence in infant mice. The CsrA Arg6His point mutant NcsrA.R6H was competed against the wild-type strain N16961G. Five-day-old suckling BALB/c mice were inoculated intragastrically with an equal number of each competing strain as described in Materials and Methods. The competitive index (CI) was calculated by normalizing the output ratio to the input ratio of the two competing strains. Each data point represents one mouse, and the median CI (0.01) is represented by the solid horizontal line. A CI value below 1 indicates that the mutant is at a competitive disadvantage. The dotted line shows the limit of detection for the CI in this experiment, which was 0.005. In 4 out of 9 mice, the mutant was not detected during analysis of more than 200 recovered colonies, and thus the CI falls below the limit of detection. These data points are included in the analysis as having a value of 0.005, which is the most conservative estimate for the CI. The actual CI values are likely to be lower. The results were statistically significant (P < 0.05) by the Mann-Whitney nonparametric test.
Mentions: ToxR is a critical virulence factor within the mammalian host (4, 33, 34), suggesting that functional CsrA may also be necessary for the pathogenesis of V. cholerae. To test this, we assessed the ability of the NcsrA.R6H mutant to colonize infant mice. The infant mouse model has been shown to be effective in demonstrating the importance of many major virulence factors in this pathogen (35). A competition assay was performed to compare the in vivo fitness of the NcsrA.R6H point mutant to that of the wild-type strain. As described earlier, the NcsrA.R6H strain was not impaired in its in vitro growth but failed to increase ToxR and OmpU levels in response to the NRES mix. Five-day-old infant mice were inoculated intragastrically with equal numbers of the wild-type strain and the NcsrA.R6H mutant. The ability of the mutant strain to compete with the wild-type strain was assessed by determining the ratio of viable mutant cells to wild-type cells recovered after 18 h. The median competitive index (CI [i.e., the output ratio normalized to the input ratio]) for the NcsrA.R6H mutant was <0.01, showing a severe defect in the ability to colonize the infant mouse (Fig. 8). Four of the nine animals yielded results that were below the limit of detection (CI, <0.005), and therefore the median CI is likely even lower than what was computed. These data point to an overall decrease in fitness of more than 100-fold for the mutant strain, showing that CsrA is critical for colonization of the small intestine.

Bottom Line: Conversely, specific amino acid substitutions in CsrA were associated with defects in ToxR production in response to NRES.Unlike previously described effects of CsrA on virulence gene regulation, the effects of CsrA on ToxR were not mediated through quorum sensing and HapR.By linking environmental sensing to the ToxR regulon, CsrA effectively acts as a switch that controls pathogenesis in response to specific signals.

View Article: PubMed Central - PubMed

Affiliation: Department of Molecular Biosciences and Institute for Cellular and Molecular Biology, The University of Texas at Austin, Austin, Texas, USA armey@austin.utexas.edu.

No MeSH data available.


Related in: MedlinePlus