Direct quantitative transcript analysis of the agr regulon of Staphylococcus aureus during human infection in comparison to the expression profile invitro

Bacteria possess a repertoire of distinct regulatory systems promoting surv ival in disparate environments. Under in vitro conditions it was demonstrat ed for the human pathogen Staphylococcus aureus that the expression of most virulence factors is coordinated by the global regulator agr. To monitor b acterial gene regulation in the host, we developed a method for direct tran script analysis from clinical specimens. Quantification of specific transcr ipts was performed by competitive reverse transcription-PCR, and results we re normalized against the constitutively expressed gene for gyrase (gyr). U sing sputum from cystic fibrosis (CP) patients infected with S. aureus we e xamined the transcription of the effector molecule RNAIII of agr, of spa (p rotein A), generally repressed by agr, and of hla (alpha-toxin), generally activated by agr. In the CF lung RNAIII was expressed poorly, indicating an inactive agr in vivo. Despite the low level of RNAIII expression, spa was detectable only in minute amounts and an irregular transcription of hla was observed in all sputum samples. After subculturing of patient strains agr deficient isolates and isolates with unusual expression profiles, i.e., not consistent with those obtained from prototypic strains, were observed. In conclusion, the agr activity seems to be nonessential in CF, and from the d escribed expression pattern of spa and hla, other regulatory circuits aside from agr are postulated in vivo.