Faculty Bibliography

Some bacterial pathogens elaborate and secrete virulence factors in response to environmental signals, others in response to a specific host product, and still others in response to no discernible cue. In this study, we have demonstrated that the synthesis of Staphylococcus aureus virulence factors is controlled by a density-sensing system that utilizes an octapeptide produced by the organism itself. The octapeptide activates expression of the agr locus, a global regulator of the virulence response. This response involves the reciprocal regulation of genes encoding surface proteins and those encoding secreted virulence factors. As cells enter the postexponential phase, surface protein genes are repressed by agr and secretory protein genes are subsequently activated. The intracellular agr effector is a regulatory RNA, RNAIII, whose transcription is activated by an agr-encoded signal transduction system for which the octapeptide is the ligand

RNAIII, an RNA molecule shown to encode delta-hemolysin and independently to regulate toxin synthesis in Staphylococcus aureus, is transcribed at the mid-exponential phase of growth, while its target genes are activated 2 h later, at the post-exponential phase of growth. We show here that the translation of RNAIII to the 26-amino acid peptide delta-hemolysin is delayed by 1 h, and that this delay is abolished when the 3'-end of this molecule is deleted. We suggest that structural changes of RNAIII to a translatable form of the molecule precede its regulation of target gene expression

Twelve episodes of Staphylococcus epidermidis bacteraemia occurred within three months in a neonatal intensive care unit. Plasmid profiles and Southern blot hybridization with five different probes were used to determine whether an endemic strain of S. epidermidis could be identified among the contemporary isolates. It was concluded that this methodology was satisfactory for differentiation between isolates of coagulase-negative staphylococci: fifteen isolates were divided in eight groups indicating that there was no single endemic strain causing the outbreak

The synthesis of virulence factors and other exoproteins in Staphylococcus aureus is controlled by the global regulator, agr. Expression of secreted proteins is up-regulated in the postexponential growth phase, whereas expression of surface proteins is down-regulated by agr. The agr locus consists of two divergent operons, transcribed from neighboring but non-overlapping promoters, P2 and P3. The P2 operon sequence, reported here, contains 4 open reading frames, agrA, C, D, and B, of which A and C appear to encode proteins of a classical 2-component signal transduction pathway. The P3 operon specifies a 0.5 kb transcript, RNA III, which is the actual effector of the agr response, and, incidentally, encodes the agr-regulated peptide delta-hemolysin. Transcriptional fusions have shown that both P2 and P3 are agr sensitive (function in an agr+ but not in an agr- background) and deletion analysis has shown that all four of the P2 ORFs are involved; agrA and agrC seem to be absolutely required for the transcriptional activation of the agr locus, whereas agrB and agrD seem to be partially required. Since transcription of P2 requires P2 operon products, the P2 operon is autocatalytic, and is thus admirably suited to the need for rapid production of exoproteins at a time when overall growth is coming to a halt

Staphylococcus aureus is a major human pathogen causing diseases which range from minor skin infection to endocarditis and toxic shock syndrome. The pathogenesis of S. aureus is due primarily to the production of toxic exoproteins, whose synthesis is controlled by a global regulatory system, agr. We show here that agr is autoinduced by a proteinaceous factor produced and secreted by the bacteria and that it is inhibited by a peptide produced by an exoprotein-deficient S. aureus mutant strain. The inhibitor, RIP, competes with the activator, RAP, and may be a mutational derivative. Our results suggest two possible approaches, independent of antibiotics, to the control of S. aureus infections. RIP may prove useful as a direct inhibitor of virulence and RAP as a vaccine against the expression of agr-induced virulence factors; either could interfere with the ability of the bacteria to establish and maintain an infection

The Staphylococcus aureus rolling circle plasmid pT181 regulates its replication by controlling the synthesis of its initiator protein RepC. RepC is inactivated during pT181 replication by the addition of an oligodeoxynucleotide, giving rise to a new form, RepC*. We analyzed RepC and RepC* in four classes of mutants: plasmid copy number mutants, two classes of RepC mutants affecting different portions of the protein and oriC (origin) mutants. We have found that in the cell with wild-type RepC there are similar relative amounts of RepC and RepC*, regardless of copy number, and that the conversion of RepC to RepC* is replication dependent. Genetic and biochemical evidence is presented that RepC functions as a dimer and that during replication the RepC homodimer is converted to the RepC/RepC* heterodimer

Expression of staphylocoagulase by agr+ Staphylococcus aureus depends on the growth phase, being maximal during exponential growth and decreasing sharply postexponentially, while an agr-deleted strain continuously expresses an intermediate level of coagulase. Therefore, coagulase expression appears to be both positively and negatively modulated by an agr-dependent mechanism

Glycerol monolaurate (GML) is a naturally occurring surfactant that is used widely as an emulsifier in the food and cosmetics industries and is generally regarded as lacking in important biological activities. The recent observation that it inhibits the production of staphylococcal toxic shock toxin-1 (P. M. Schlievert, J. R. Deringer, M. H. Kim, S. J. Projan, and R. P. Novick, Antimicrob. Agents Chemother. 36:626-631, 1992) is therefore rather surprising and raises the interesting question of how such a compound might interact with cells. In this report, we show that GML inhibits the synthesis of most staphylococcal toxins and other exoproteins and that it does so at the level of transcription. We find that GML blocks the induction but not the constitutive synthesis of beta-lactamase, suggesting that it acts by interfering with signal transduction