Accessory Gene Regulator Locus of Staphylococcus intermedius

The accessory gene regulator (agr) locus, a candidate system forthe regulation of the production of virulence factors inStaphylococcus intermedius, has beencharacterized. Using PCR-based genome walking, we haveobtained the first complete sequence (3,436 bp) of the accessory generegulator (agr) gene in this organism. Sequence analysis ofthe agr gene has identified five open reading frames (ORFs),agrB, agrD, agrC, agrA, andhld. The translated ORF contained amino acid motifscharacteristic of the response regulator and histidine protein kinasesignal transducer of the classic two-component regulatory system.Sequencing of the agrD PCR products amplified from DNA from 20different isolates has facilitated detection of genetic variation inthe putative autoinducing peptide (AIP) within the agr gene ofS. intermedius, revealing the presence of at leastthree agr specificity groups within this species.Classification of the agr gene from S.intermedius was supported by phylogenetic analysis. Real-timePCR also revealed that the effector molecule of the agrsystem, RNAIII, was regulated in an autocrine manner inS. intermedius and demonstrated positive correlationwith the temporal gene expression patterns of luk andentC. Transcription of RNAIII was also dependent on selfsecreted cues. Cyclic self and nonself peptides were synthesized on thebasis of the novel AIPs produced by S. intermedius,which lack the cysteine necessary to form the thiolactone ring inanalogous peptides from Staphylococcus aureus andStaphylococcus epidermidis. Experiments with thesesynthetic cyclic peptides indicated that self peptides led toup-regulation of RNAIII--findings in support of the assumptionthat activation of the agr gene is initiated by growth- andspecies-specific factors generated during bacterialgrowth.