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A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues
07:10

A Fluorescence-based Method to Study Bacterial Gene Regulation in Infected Tissues

Published on: February 19, 2019

Thymidine-dependent Staphylococcus aureus small-colony variants are associated with extensive alterations in

Barbara C Kahl1, Gunnar Belling, Petra Becker

  • 1Institute of Medical Microbiology, University Clinics of Muenster, Domagkstr. 10, 48149 Muenster, Germany. kahl@uni-muenster.de

Infection and Immunity
|June 24, 2005
PubMed

Insights

Small-colony variants (SCVs) of Staphylococcus aureus are thymidine-dependent and resistant to trimethoprim-sulfamethoxazole (SXT). These SCVs exhibit reduced virulence gene expression and altered growth, aiding their persistence in cystic fibrosis airways.

Area of Science:

  • Microbiology
  • Infectious Diseases
  • Genetics

Background:

  • Chronic airway infection is characteristic of cystic fibrosis (CF).
  • Staphylococcus aureus, particularly trimethoprim-sulfamethoxazole (SXT)-resistant small-colony variants (SCVs), frequently causes persistent infections in CF patients.
  • Long-term SXT therapy contributes to the prevalence of SXT-resistant S. aureus SCVs.

Purpose of the Study:

  • To compare the transcriptional profiles of regulator and virulence genes in S. aureus SCVs versus normal strains.
  • To investigate the impact of SCV characteristics on bacterial adaptation and survival in the CF airway environment.

Main Methods:

  • Growth curve analyses were performed to assess doubling times and final densities.
  • Transcriptional analysis, including reverse transcription-PCR and Northern analysis, was used to measure the expression of key regulator genes (sigB, sarA, agr) and virulence genes (hla, spa).
  • The effect of thymidine supplementation and agr quorum-sensing system activation on SCV gene expression was evaluated.

Main Results:

  • SCVs displayed longer doubling times and lower final densities compared to normal S. aureus strains.
  • Expression of regulator genes (sigB, sarA, agr) was significantly decreased in nearly all SCVs.
  • Virulence gene expression showed diminished alpha-hemolysin (hla) signals in all SCVs and increased protein A (spa) signals in some SCVs.
  • Thymidine supplementation and agr activation partially restored gene transcription to normal levels.

Conclusions:

  • Multiple alterations in growth characteristics and regulator/virulence gene expression contribute to the reduced virulence of S. aureus SCVs.
  • These adaptations enable SCVs to survive in the challenging CF airway environment, highlighting bacterial adaptation during chronic persistence.
  • Understanding these mechanisms is crucial for developing strategies to combat persistent S. aureus infections in cystic fibrosis.

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