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Phenotypic Variation Is Almost Entirely Independent of the Host-Pathogen Relationship in Clinical Isolates of S. aureus.

Land AD, Hogan P, Fritz S, Levin PA - PLoS ONE (2015)

Bottom Line: Biofilm formation, hemolysis and pigment formation have all been associated with virulence in mice.One exception was a small, but significant, correlation between an increased propensity for biofilm formation and isolation from skin and soft tissue infections (SSTIs).These data suggest the existence of significant evolutionary pressure on the S. aureus genome and highlight a role for host factors as a strong determinant of the host-pathogen relationship.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Washington University in Saint Louis, Saint Louis, Missouri, United States of America.

ABSTRACT

Background: A key feature of Staphylococcus aureus biology is its ability to switch from an apparently benign colonizer of ~30% of the population to a cutaneous pathogen, to a deadly invasive pathogen. Little is known about the mechanisms driving this transition or the propensity of different S. aureus strains to engender different types of host-pathogen interactions. At the same time, significant weight has been given to the role of specific in vitro phenotypes in S. aureus virulence. Biofilm formation, hemolysis and pigment formation have all been associated with virulence in mice.

Design: To determine if there is a correlation between in vitro phenotype and the three types of host-pathogen relationships commonly exhibited by S. aureus in the context of its natural human host, we assayed 300 clinical isolates for phenotypes implicated in virulence including hemolysis, sensitivity to autolysis, and biofilm formation. For comparative purposes, we also assayed phenotype in 9 domesticated S. aureus strains routinely used for analysis of virulence determinants in laboratory settings.

Results: Strikingly, the clinical strains exhibited significant phenotypic uniformity in each of the assays evaluated in this study. One exception was a small, but significant, correlation between an increased propensity for biofilm formation and isolation from skin and soft tissue infections (SSTIs). In contrast, we observed a high degree of phenotypic variation between common laboratory strains that exhibit virulence in mouse models. These data suggest the existence of significant evolutionary pressure on the S. aureus genome and highlight a role for host factors as a strong determinant of the host-pathogen relationship. In addition, the high degree of variation between laboratory strains emphasizes the need for caution when applying data obtained in one lab strain to the analysis of another.

No MeSH data available.


Related in: MedlinePlus

Colony morphology and growth rate variability in reference strains of S. aureus.(A) Domesticated strains of S. aureus were streaked onto TSA plates and grown overnight at 37°C. Following incubation images were observed for differences in color and size. (B) We observed S. aureus isolates relative growth rates, cell density, and survival potential in stationary phase. Single colonies of S. aureus were inoculated into TSB and grown overnight at 37°C with shaking. Following overnight incubation cultures are diluted back to an OD600 of ~0.05 grown at 37°C with shaking. Optical density was measured every 30 minutes.
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pone.0129670.g001: Colony morphology and growth rate variability in reference strains of S. aureus.(A) Domesticated strains of S. aureus were streaked onto TSA plates and grown overnight at 37°C. Following incubation images were observed for differences in color and size. (B) We observed S. aureus isolates relative growth rates, cell density, and survival potential in stationary phase. Single colonies of S. aureus were inoculated into TSB and grown overnight at 37°C with shaking. Following overnight incubation cultures are diluted back to an OD600 of ~0.05 grown at 37°C with shaking. Optical density was measured every 30 minutes.

Mentions: Comparisons of the growth rates of each domesticated staphylococcal strain revealed very few differences in cell densities and mass doubling times. As expected the VISA strain Mu50 grew substantially slower in Tryptic Soy Broth (TSB) when compared to the other reference strains (Fig 1B). This growth property is common amongst VISA isolates and is thought to be due to defects in cell wall biosynthesis [14]. Also Mu50, plated on TSA plates appeared smaller by visual analysis, than the related N315 strain and the other laboratory strains. Observations of the domesticated laboratory strains plated on TSB agar revealed a distinct difference in the pigmentation of SH1000 and its progenitor strain NCTC 8325 (Fig 1A). Comparisons of the two USA300 strains directly exhibited differences in both growth rates and yields. USA300 TCH1516 grows slower in TSB media than its subclone USA300 FPR3757 (Fig 1B). There were also morphological distinctions when comparing the three USA300 strains. TCH1516 formed small, unpigmented colonies on TSA plates, while FPR3757 and MW2 both formed larger golden colonies under identical growth conditions (Fig 1A).


Phenotypic Variation Is Almost Entirely Independent of the Host-Pathogen Relationship in Clinical Isolates of S. aureus.

Land AD, Hogan P, Fritz S, Levin PA - PLoS ONE (2015)

Colony morphology and growth rate variability in reference strains of S. aureus.(A) Domesticated strains of S. aureus were streaked onto TSA plates and grown overnight at 37°C. Following incubation images were observed for differences in color and size. (B) We observed S. aureus isolates relative growth rates, cell density, and survival potential in stationary phase. Single colonies of S. aureus were inoculated into TSB and grown overnight at 37°C with shaking. Following overnight incubation cultures are diluted back to an OD600 of ~0.05 grown at 37°C with shaking. Optical density was measured every 30 minutes.
© Copyright Policy
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4476556&req=5

pone.0129670.g001: Colony morphology and growth rate variability in reference strains of S. aureus.(A) Domesticated strains of S. aureus were streaked onto TSA plates and grown overnight at 37°C. Following incubation images were observed for differences in color and size. (B) We observed S. aureus isolates relative growth rates, cell density, and survival potential in stationary phase. Single colonies of S. aureus were inoculated into TSB and grown overnight at 37°C with shaking. Following overnight incubation cultures are diluted back to an OD600 of ~0.05 grown at 37°C with shaking. Optical density was measured every 30 minutes.
Mentions: Comparisons of the growth rates of each domesticated staphylococcal strain revealed very few differences in cell densities and mass doubling times. As expected the VISA strain Mu50 grew substantially slower in Tryptic Soy Broth (TSB) when compared to the other reference strains (Fig 1B). This growth property is common amongst VISA isolates and is thought to be due to defects in cell wall biosynthesis [14]. Also Mu50, plated on TSA plates appeared smaller by visual analysis, than the related N315 strain and the other laboratory strains. Observations of the domesticated laboratory strains plated on TSB agar revealed a distinct difference in the pigmentation of SH1000 and its progenitor strain NCTC 8325 (Fig 1A). Comparisons of the two USA300 strains directly exhibited differences in both growth rates and yields. USA300 TCH1516 grows slower in TSB media than its subclone USA300 FPR3757 (Fig 1B). There were also morphological distinctions when comparing the three USA300 strains. TCH1516 formed small, unpigmented colonies on TSA plates, while FPR3757 and MW2 both formed larger golden colonies under identical growth conditions (Fig 1A).

Bottom Line: Biofilm formation, hemolysis and pigment formation have all been associated with virulence in mice.One exception was a small, but significant, correlation between an increased propensity for biofilm formation and isolation from skin and soft tissue infections (SSTIs).These data suggest the existence of significant evolutionary pressure on the S. aureus genome and highlight a role for host factors as a strong determinant of the host-pathogen relationship.

View Article: PubMed Central - PubMed

Affiliation: Department of Biology, Washington University in Saint Louis, Saint Louis, Missouri, United States of America.

ABSTRACT

Background: A key feature of Staphylococcus aureus biology is its ability to switch from an apparently benign colonizer of ~30% of the population to a cutaneous pathogen, to a deadly invasive pathogen. Little is known about the mechanisms driving this transition or the propensity of different S. aureus strains to engender different types of host-pathogen interactions. At the same time, significant weight has been given to the role of specific in vitro phenotypes in S. aureus virulence. Biofilm formation, hemolysis and pigment formation have all been associated with virulence in mice.

Design: To determine if there is a correlation between in vitro phenotype and the three types of host-pathogen relationships commonly exhibited by S. aureus in the context of its natural human host, we assayed 300 clinical isolates for phenotypes implicated in virulence including hemolysis, sensitivity to autolysis, and biofilm formation. For comparative purposes, we also assayed phenotype in 9 domesticated S. aureus strains routinely used for analysis of virulence determinants in laboratory settings.

Results: Strikingly, the clinical strains exhibited significant phenotypic uniformity in each of the assays evaluated in this study. One exception was a small, but significant, correlation between an increased propensity for biofilm formation and isolation from skin and soft tissue infections (SSTIs). In contrast, we observed a high degree of phenotypic variation between common laboratory strains that exhibit virulence in mouse models. These data suggest the existence of significant evolutionary pressure on the S. aureus genome and highlight a role for host factors as a strong determinant of the host-pathogen relationship. In addition, the high degree of variation between laboratory strains emphasizes the need for caution when applying data obtained in one lab strain to the analysis of another.

No MeSH data available.


Related in: MedlinePlus