Thymidine-dependent Staphylococcus aureus small-colony variants are associated with extensive alterations in regulator and virulence gene expression profiles - PubMed (original) (raw)

Thymidine-dependent Staphylococcus aureus small-colony variants are associated with extensive alterations in regulator and virulence gene expression profiles

Barbara C Kahl et al. Infect Immun. 2005 Jul.

Abstract

Chronic airway infection is a hallmark of cystic fibrosis (CF) and many CF patients are infected persistently by Staphylococcus aureus. Thymidine-dependent trimethoprim-sulfamethoxazole (SXT)-resistant S. aureus small-colony variants (SCVs), often in combination with isogenic normal S. aureus phenotypes, are highly prevalent and persistent in airway secretions of CF patients due to long-term SXT therapy (B. Kahl, M. Herrmann, A. S. Everding, H. G. Koch, K. Becker, E. Harms, R. A. Proctor, and G. Peters, J. Infect. Dis. 177:1023-1029, 1998). In this report, SCVs were compared to normal S. aureus by transcription analysis of important regulator (sigB, sarA, and agr) and virulence (alpha-hemolysin, hla, and protein A, spa) genes. Growth curve analyses revealed longer doubling times and lower final densities for SCVs than for normal strains. sigB activity was measured by transcription analysis of the sigB target gene asp23. For nearly all SCVs, expression of all regulators was decreased as assessed by asp23 reverse transcription-PCR for sigB and Northern analysis for sarA and agr. These results are in agreement with diminished hla signals in all SCVs and increased spa signals in 5 of 10 SCVs compared to the isogenic normal S. aureus. Both supplementation of SCVs with thymidine and activation of the agr quorum-sensing system by the supernatant of the isogenic normal strain reversed transcription to almost normal levels. In conclusion, multiple changes in growth characteristics and in regulator and virulence gene expression render SCVs less virulent and allow them to survive in the hostile environment present in the airways of CF patients, thereby illustrating adaptation of the bacteria during long-term persistence.

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Figures

FIG. 1.

FIG. 1.

Growth phase analysis and transcription profiles of a normal S. aureus strain, the isogenic thymidine-dependent SCV with fried-egg appearance, and the SCV supplemented with thymidine. (A) For growth phase analysis (strain pair 1), bacteria were cultured in BHI or BHI supplemented with 100 μg/ml thymidine on a rotary shaker at 37°C. Every hour, bacteria were harvested and the optical density at 578 nm was determined. (B) Transcription analysis of sarA, RNAIII, hla, and spa of the normal S. aureus strain 5, its isogenic thymidine-dependent SCV with fried-egg appearance, and the SCV supplemented with 100 μg/ml thymidine, representative for typical transcription patterns as found in other SCV-normal strain pairs with fried-egg appearances. RNA was harvested at early log phase (EL), late log phase (LL), and stationary phase (SP). Ten micrograms of total RNA was applied to each lane.

FIG. 2.

FIG. 2.

Growth phase analysis and transcription profiles of a normal S. aureus strain, the isogenic thymidine-dependent SCV with pinpoint phenotype, and the SCV supplemented with thymidine (strain pair 10). (A) For growth phase analysis, bacteria were cultured in BHI or BHI supplemented with 100 μg/ml thymidine on a rotary shaker at 37°C. Every hour, bacteria were harvested and the optical density was determined at 578 nm. (B) Transcription analysis of sarA, RNAIII, hla, and spa of a normal S. aureus strain, the isogenic thymidine-dependent SCV with pinpoint phenotype, and the SCV supplemented with 100 μg/ml thymidine, representative for typical transcription patterns as found in other pinpoint SCV-normal strain pairs. RNA was harvested at early log, late-log, and stationary phases. Ten micrograms of total RNA was applied to each lane.

FIG. 3.

FIG. 3.

agr activation of SCV strains by the AIP of the isogenic normal S. aureus strain. To determine if the agr regulon of SCVs can be activated by the AIP of the isogenic normal S. aureus, the supernatant of the normal strain was prepared after overnight culture and added to SCV and to normal growth cultures at the indicated time points. As a control, BHI broth alone was added to SCV and normal cultures.

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References

    1. Balwit, J. M., P. van Langefelde, J. M. Vann, and R. A. Proctor. 1994. Gentamicin-resistant menadione and hemin auxotrophic Staphylococcus aureus persist within cultured endothelial cells. J. Infect. Dis. 170:1033-1037. - PubMed
    1. Bayer, M. G., J. H. Heinrichs, and A. L. Cheung. 1996. The molecular architecture of the sar locus in Staphylococcus aureus. J. Bacteriol. 178:4563-4570. - PMC - PubMed
    1. Bischoff, M., J. M. Entenza, and P. Giachino. 2001. Influence of a functional sigB operon on the global regulators sar and agr in Staphylococcus aureus. J. Bacteriol. 183:5171-5179. - PMC - PubMed
    1. Branger, C., C. Gardye, and N. Lambert-Zechovsky. 1996. Persistence of Staphylococcus aureus strains among cystic fibrosis patients over extended periods of time. J. Med. Microbiol. 45:294-301. - PubMed
    1. Burns, J. L., J. Emerson, J. R. Stapp, D. L. Yim, J. Krzewinski, L. Louden, B. W. Ramsey, and C. R. Clausen. 1998. Microbiology of sputum from patients at cystic fibrosis centers in the United States. Clin. Infect. Dis. 27:158-163. - PubMed

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