Impact of the regulatory loci agr, sarA and sae of Staphylococcus aureus on the induction of α‐toxin during device‐related infection resolved by direct quantitative transcript analysis

• Published in: Molecular microbiology 2001-06, Vol.40 (6), p.1439-1447
• Main Authors: Goerke, Christiane, Fluckiger, Ursula, Steinhuber, Andrea, Zimmerli, Werner, Wolz, Christiane
• Format: Article
• Language: English
• Subjects: a-toxin; agr gene; Animals; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Bacterial Toxins - genetics; Bacterial Toxins - metabolism; Cystic Fibrosis - microbiology; Exudates and Transudates; Gene Expression Regulation, Bacterial; Genes, Regulator; Guinea Pigs; Hemolysin Proteins - genetics; Hemolysin Proteins - metabolism; hla gene; Humans; Mutation; Prosthesis-Related Infections - genetics; Prosthesis-Related Infections - microbiology; Reverse Transcriptase Polymerase Chain Reaction; sae gene; sarA gene; Staphylococcal Infections - genetics; Staphylococcal Infections - microbiology; Staphylococcus aureus; Staphylococcus aureus - genetics; Staphylococcus aureus - pathogenicity; Trans-Activators; Transcription Factors
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1046/j.1365-2958.2001.02494.x

The cytotoxic α‐toxin (encoded by hla) of Staphylococcus aureus is regulated by three loci, agr, sarA and sae, in vitro. Here, we assess the regulation of hla in a guinea pig model of device‐related infection by quantifying RNAIII (the effector molecule of agr) and hla directly in exudates accumulating in infected devices without subculturing of the bacteria. LightCycler reverse transcription–polymerase chain reaction (RT–PCR) was used to quantify the transcripts. Strains RN6390 and Newman expressed considerably smaller amounts of RNAIII in the guinea pig than during in vitro growth. The residual RNAIII expression decreased during the course of infection and was negatively correlated with bacterial densities. As with RNAIII, the highest hla expression was detected in both strains early in infection. Even in strain Newman, a weak hla producer in vitro, a pronounced expression of hla was observed during infection. Likewise, four S. aureus isolates from cystic fibrosis (CF) patients expressed hla despite an inactive agr during device‐related infection as in the CF lung. Mutation of agr and sarA in strain Newman and RN6390 had no consequence for hla expression in vivo. In contrast, the mutation in sae resulted in severe downregulation of hla in vitro as well as in vivo. In conclusion, S. aureus seems to be provided with regulatory circuits different from those characterized in vitro to ensure α‐toxin synthesis during infections.