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Glucose and nonmaintained pH decrease expression of the accessory gene regulator (agr) in Staphylococcus aureus.

L B Regassa1, R P Novick, M J Betley

  • 1University of Wisconsin-Madison 53706.

Infection and Immunity
|August 1, 1992
PubMed
Summary
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Glucose significantly reduces accessory gene regulator (agr) expression in Staphylococcus aureus, impacting virulence factors. This effect is pronounced at low or unmaintained pH levels, highlighting glucose

Area of Science:

  • Microbiology
  • Molecular Biology
  • Bacterial Pathogenesis

Background:

  • The accessory gene regulator (agr) is a global regulatory system in Staphylococcus aureus that controls the expression of numerous virulence factors.
  • The agr system comprises two transcripts, RNAII and RNAIII, with RNAIII playing a key role in regulating target genes like alpha-hemolysin (hla) and staphylococcal enterotoxin B (sec+).
  • Mechanisms governing agr-mediated regulation are not fully understood, prompting investigation into environmental factors influencing its expression.

Purpose of the Study:

  • To investigate the impact of glucose on accessory gene regulator (agr) expression in Staphylococcus aureus.
  • To determine how glucose affects the expression of agr target genes, specifically sec+ and hla.
  • To elucidate the interplay between glucose concentration, pH, and agr expression.

Related Experiment Videos

Main Methods:

  • Culturing Staphylococcus aureus in both complex medium (shake flask) and defined medium (fermentor) with controlled pH and glucose levels.
  • Utilizing Northern (RNA) blot analysis to quantify agr expression levels.
  • Assessing the expression of agr target genes sec+ and hla under varying glucose and pH conditions.

Main Results:

  • A significant reduction in agr expression was observed in the presence of glucose, particularly at pH 5.5 or when pH was not maintained.
  • Glucose-containing cultures exhibited decreased expression of sec+ and hla mRNA, even at a maintained pH of 6.5.
  • The inhibitory effect of glucose on sec+ and hla expression was amplified under conditions that also suppressed agr expression (pH 5.5 or unmaintained pH).

Conclusions:

  • Glucose acts as a potent inhibitor of accessory gene regulator (agr) expression in Staphylococcus aureus.
  • This glucose-mediated repression of agr consequently downregulates the expression of key virulence genes like sec+ and hla.
  • The findings underscore the importance of environmental factors, such as glucose availability and pH, in modulating Staphylococcus aureus virulence potential.