Inactivation of traP Has No Effect on the Agr Quorum-Sensing System or Virulence of Staphylococcus aureus

Abstract

The success of Staphylococcus aureus as a pathogen can largely be attributed to the plethora of genetic regulators encoded within its genome that temporally regulate its arsenal of virulence determinants throughout its virulence lifestyle. Arguably the most important of these is the two-component, quorum-sensing system agr. Over the last decade, the controversial presence of a second quorum-sensing system (the TRAP system) has been proposed, and it has been mooted to function as the master regulator of virulence in S. aureus by modulating agr. Mutants defective in TRAP are reported to be devoid of agr expression, lacking in hemolytic activity, essentially deficient in the secretion of virulence determinants, and avirulent in infection models. A number of research groups have questioned the validity of the TRAP findings in recent years; however, a thorough and independent analysis of its role in S. aureus physiology and pathogenesis has not been forthcoming. Therefore, we have undertaken such an analysis of the TRAP locus of S. aureus. We found that a traP mutant was equally hemolytic as the wild-type strain. Furthermore, transcriptional profiling found no alterations in the traP mutant in expression levels of agr or in expression levels of multiple agr-regulated genes (hla, sspA, and spa). Analysis of secreted and surface proteins of the traP mutant revealed no deviation in comparison to the parent. Finally, analysis conducted using a murine model of S. aureus septic arthritis revealed that, in contrast to an agr mutant, the traP mutant was just as virulent as the wild-type strain.Staphylococcus aureus is a major human pathogen that is considered to be one of the most common causes of human disease (42). The success of S. aureus as an infectious agent is largely due to its ability to cause a wide range of infections in a plethora of ecological niches within the host. These can range from the relatively benign, such as soft tissue infections, boils, and abscesses, to the systemic and life threatening, such as endocarditis, septic arthritis, osteomyelitis, pneumonia, and septicemia. The array of pathologies caused by S. aureus is facilitated by the arsenal of virulence determinants encoded within its genome, all of which are tightly regulated both temporally and spatially throughout its pathogenic life cycle (42,51). This is achieved through an army of regulatory mechanisms that encompass DNA-binding proteins, two-component regulators, sigma factors, and quorum-sensing mechanisms (1, 3, 12, 15-18, 22, 26, 30, 32, 34, 51, 71).Arguably the most important of all of these regulatory loci is the agr system, a quorum-sensing two-component regulator that has been shown by numerous investigators to be central to the infectious capacity of S. aureus (1,34,47,49,55). Agr is a temporal regulatory element that is maximally expressed from the postexponential phase onwards, where it represses surface and attachment proteins and upregulates the synthesis of toxins and exoenzymes. Upon entry into stationary phase, agr expression...

A Nonsense Mutation in agrA Accounts for the Defect in agr Expression and the Avirulence of Staphylococcus aureus 8325-4 traP :: kan

“…This mutation is responsible for the failure of the traP mutant to express agr, for its avirulence in the murine abscess model (5), and for the identity of the traP transcriptome with that of agr (7). These findings are entirely consistent with two other reports (15,20) demonstrating that traP mutations have no effect on agr expression or virulence. …”

Identification of an intracellular M17 family leucine aminopeptidase that is required for virulence in Staphylococcus aureus

“…β–galactosidase assays were performed with 4-MUG as a substrate, as described by us previously [29, 31], with the following modification. β–galactosidase activity is expressed as arbitrary units corresponding to the value of light units released divided by the bacterial cfu per sample.…”

agr RNAIII divergently regulates glucose-induced biofilm formation in clinical isolates of Staphylococcus aureus

“…Previous studies have provided strong evidence that the only agr-activating component in the supernatant of S. aureus isolates that are Agr + is related to the presence of AIP (Novick et al 2000;Shaw et al 2007). Thus, beside RNAIII complementation, the agr interference using conditioned medium (Ji et al, 1997) could provide a simple and straightforward experiment to quickly recheck the effect of agr in S. aureus biofilm formation on microtitre plates.…”