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Persistent Staphylococcus aureus isolates from two independent cases of bacteremia display increased bacterial fitness and novel immune evasion phenotypes.

Richards RL, Haigh RD, Pascoe B, Sheppard SK, Price F, Jenkins D, Rajakumar K, Morrissey JA - Infect. Immun. (2015)

Bottom Line: Several novel traits were associated specifically with both independent sets of persistent S. aureus isolates compared to both the initial isolates and the isolates from resolved infections (resolved isolates).These traits included (i) increased growth under nutrient-poor conditions; (ii) increased tolerance of iron toxicity; (iii) higher expression of cell surface proteins involved in immune evasion and stress responses; and (iv) attenuated virulence in a Galleria mellonella larva infection model that was not associated with small-colony variation or metabolic dormancy such as had been seen previously.Overall, our data indicate a novel role for MprF function during development of S. aureus persistence by increasing bacterial fitness and immune evasion.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics and Infection, Immunity of Inflammation, University of Leicester, Leicester, United Kingdom.

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DNase and hemolysin activity. (A and B) Alpha (A) and beta (B) hemolytic activities were assessed as the final dilution (DF, dilution factor) of concentrated bacterial supernatant where complete hemolysis still occurred. Dilution factor means were calculated and plotted from the results of three independent experiments ± 1 standard deviation. (C) DNase activity was assessed by measuring the size (in millimeters) of the halo around the test isolates indicating hydrolyzed DNA. Means were calculated and plotted from the results of three independent experiments ± 1 standard deviation.
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Figure 4: DNase and hemolysin activity. (A and B) Alpha (A) and beta (B) hemolytic activities were assessed as the final dilution (DF, dilution factor) of concentrated bacterial supernatant where complete hemolysis still occurred. Dilution factor means were calculated and plotted from the results of three independent experiments ± 1 standard deviation. (C) DNase activity was assessed by measuring the size (in millimeters) of the halo around the test isolates indicating hydrolyzed DNA. Means were calculated and plotted from the results of three independent experiments ± 1 standard deviation.

Mentions: Persistent S. aureus bacteremia isolates have previously been associated with decreased toxin expression and activity, particularly of alpha-hemolysin, usually in combination with a recognized SCV phenotype and/or agr dysfunction (11, 13, 18, 19). No differences were found between the initial, persistent, and resolved MRSA bacteremia isolates with regard to alpha-hemolysin, beta-hemolysin, and DNase activity or cell wall covalently bound protein profiles in this study (Fig. 4 and unpublished data). However, several reproducible differences between the persistent, initial, and resolved EMRSA-15 bacteremia isolates in the non-covalently bound cell surface-associated protein fraction after growth in nutrient- and metal ion-restricted CRPMI medium were recorded. To identify individual proteins, quantitative proteomic profiling was conducted using iTRAQ (isobaric tag for relative and absolute quantification) coupled with LC-MS (liquid chromatography-mass spectrometry). The iTRAQ–LC-MS analysis identified 214 and 178 individual proteins in each biological repeat across the full set of isolates tested, and mean relative protein values were calculated. Those proteins which exhibited >0.5 log2-fold differences (P > 0.05) in abundance between each persistent or resolved MRSA bacteremia isolate and the respective initial isolate are listed in Tables 3 and 4, and the data are summarized in Fig. 5.


Persistent Staphylococcus aureus isolates from two independent cases of bacteremia display increased bacterial fitness and novel immune evasion phenotypes.

Richards RL, Haigh RD, Pascoe B, Sheppard SK, Price F, Jenkins D, Rajakumar K, Morrissey JA - Infect. Immun. (2015)

DNase and hemolysin activity. (A and B) Alpha (A) and beta (B) hemolytic activities were assessed as the final dilution (DF, dilution factor) of concentrated bacterial supernatant where complete hemolysis still occurred. Dilution factor means were calculated and plotted from the results of three independent experiments ± 1 standard deviation. (C) DNase activity was assessed by measuring the size (in millimeters) of the halo around the test isolates indicating hydrolyzed DNA. Means were calculated and plotted from the results of three independent experiments ± 1 standard deviation.
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC4496624&req=5

Figure 4: DNase and hemolysin activity. (A and B) Alpha (A) and beta (B) hemolytic activities were assessed as the final dilution (DF, dilution factor) of concentrated bacterial supernatant where complete hemolysis still occurred. Dilution factor means were calculated and plotted from the results of three independent experiments ± 1 standard deviation. (C) DNase activity was assessed by measuring the size (in millimeters) of the halo around the test isolates indicating hydrolyzed DNA. Means were calculated and plotted from the results of three independent experiments ± 1 standard deviation.
Mentions: Persistent S. aureus bacteremia isolates have previously been associated with decreased toxin expression and activity, particularly of alpha-hemolysin, usually in combination with a recognized SCV phenotype and/or agr dysfunction (11, 13, 18, 19). No differences were found between the initial, persistent, and resolved MRSA bacteremia isolates with regard to alpha-hemolysin, beta-hemolysin, and DNase activity or cell wall covalently bound protein profiles in this study (Fig. 4 and unpublished data). However, several reproducible differences between the persistent, initial, and resolved EMRSA-15 bacteremia isolates in the non-covalently bound cell surface-associated protein fraction after growth in nutrient- and metal ion-restricted CRPMI medium were recorded. To identify individual proteins, quantitative proteomic profiling was conducted using iTRAQ (isobaric tag for relative and absolute quantification) coupled with LC-MS (liquid chromatography-mass spectrometry). The iTRAQ–LC-MS analysis identified 214 and 178 individual proteins in each biological repeat across the full set of isolates tested, and mean relative protein values were calculated. Those proteins which exhibited >0.5 log2-fold differences (P > 0.05) in abundance between each persistent or resolved MRSA bacteremia isolate and the respective initial isolate are listed in Tables 3 and 4, and the data are summarized in Fig. 5.

Bottom Line: Several novel traits were associated specifically with both independent sets of persistent S. aureus isolates compared to both the initial isolates and the isolates from resolved infections (resolved isolates).These traits included (i) increased growth under nutrient-poor conditions; (ii) increased tolerance of iron toxicity; (iii) higher expression of cell surface proteins involved in immune evasion and stress responses; and (iv) attenuated virulence in a Galleria mellonella larva infection model that was not associated with small-colony variation or metabolic dormancy such as had been seen previously.Overall, our data indicate a novel role for MprF function during development of S. aureus persistence by increasing bacterial fitness and immune evasion.

View Article: PubMed Central - PubMed

Affiliation: Department of Genetics and Infection, Immunity of Inflammation, University of Leicester, Leicester, United Kingdom.

Show MeSH
Related in: MedlinePlus