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L B Regassa

Publications and source records attributed to L B Regassa.

4 recordsLinked to original sources
PubMed1992

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

The effect of glucose on accessory gene regulator (agr) expression in Staphylococcus aureus was examined. agr is a global regulator that affects the expression of numerous genes, including those for some factors implicated in virulence, such as toxic shock syndrome toxin 1, alpha-hemolysin, and protein A. The agr locus determines two divergent transcripts, designated RNAII and RNAIII. RNAII contains four open reading frames (agrABCD), and RNAIII encodes delta-hemolysin. The mechanisms responsible for agr-mediated regulation are not well understood, but it appears that the RNAIII transcript plays a central role in the regulation of a number of target genes, including those for alpha-hemolysin (hla), beta-hemolysin (hlb), protein A (spa), and staphylococcal enterotoxin B (seb+). In this study, S. aureus cultures were grown either in a shake flask system with a complex medium or in a fermentor system with a completely defined medium in which the pH and glucose concentration were maintained. Northern (RNA) blot analysis revealed that a dramatic reduction in agr expression was apparent only when the cultures contained glucose and when the pH was 5.5 or was not maintained. The effect of glucose on two agr target genes, sec+ and hla, was also studied. Glucose-containing cultures produced less sec+ and hla mRNAs at maintained pH (6.5). In addition, the glucose effect on sec+ and hla was enhanced under conditions that inhibited agr expression (i.e., pH 5.5 or a nonmaintained pH).

Fermentation↗
PubMed1992

Alkaline pH decreases expression of the accessory gene regulator (agr) in Staphylococcus aureus.

The effect of alkaline pH on expression of the accessory gene regulator (agr) in Staphylococcus aureus was examined. agr, a global regulator, affects the expression of numerous exoproteins, including alpha-hemolysin, toxic shock syndrome toxin 1, protein A, and staphylococcal enterotoxins types B, C, and D. agr contains two major, divergent transcripts, designated RNAII and RNAIII. In this study, the level of RNAIII was used to monitor agr expression because this transcript and/or its protein product(s) appears to be responsible for altering target gene expression. S. aureus FRI1230 and its Agr- derivative were examined in a fermentor system which allowed batch cultures to be maintained at a constant pH. FRI1230 cultures were grown at pH 6.5, 7.0, 7.5, and 8.0. Northern (RNA blot) analysis of samples revealed that maximal agr expression occurred at pH 7.0, with virtually no RNAIII observed at pH 8.0. The effect of alkaline pH on an agr target gene, sec, was also evaluated. sec expression was reduced at alkaline pH in strain FRI1230 (Agr+) but not in its Agr- derivative, indicating that an intact agr allele is required for the pH effect on sec. Examination of batch cultures under conditions of nonmaintained pH gave results that were also consistent with a role for alkaline pH in repressing agr expression.

Bacterial Toxins↗
PubMed1991

Steady-state staphylococcal enterotoxin type C mRNA is affected by a product of the accessory gene regulator (agr) and by glucose.

The effects of the accessory gene regulator (agr) and glucose on staphylococcal enterotoxin type C (SEC) gene (sec+) expression were examined. For the agr studies, a Tn551 insertionally inactivated agr was transferred into two different sec+ Staphylococcus aureus strains. Western blot (immunoblot) analysis showed that each of the sec+ Agr- derivatives produced less extracellular SEC than their Agr+ parent strains. Analysis of Northern (RNA) blots was consistent with at least part of the agr effect being at the level of steady-state sec+ mRNA. We examined the glucose effect on sec+ expression by utilizing both a fermentor system with a completely defined amino acid-containing medium in which the pH of the medium was maintained at 6.5 and a shake flask system with a complex medium in which the pH was allowed to fluctuate during bacterial growth. In both systems, samples from the cultures containing glucose had less extracellular SEC and less steady-state sec+ mRNA compared with the control cultures which lacked glucose. An intact agr was not required for the glucose effect on sec+ expression; MJB407, an Agr- sec+ strain, produced more SEC and had more steady-state sec+ mRNA when grown in medium that lacked glucose compared with medium that contained glucose.

Blotting, Northern↗