Abstract: Objective To investigate the effect of Pseudomonas quinolone signal (PQS) on the virulence of Pseudomonas aeruginosa.
Methods Pseudomonas aeruginosa strain PAO1 was treated with PQS alone, PQS plus farnesol, or farnesol alone. The
transcriptional levels of the regulator gene ExsA and virulence protein gene ExoS of type III secretion system were examined
using quantitative real-time PCR, and spectrophotometry was employed to detect pyocyanin production in the bacteria. The
adhesion and invasiveness of the treated PAO1 in cultured alveolar epithelial cells A549 were assessed on plate count agar, and
their effects on the survival of a mouse model of peritonitis was compared. Results The increase or decrease of PQS did not
affect the growth of PAO1. Compared with the untreated bacteria, PQS-treated PAO1 showed obviously increased
transcription levels of ExsA and ExoS (P<0.01) and pyocyanin production, which was significantly lowered by farnesol (P<
0.01). In A549 cell cultures, farnesol-treated PAO1 exhibited significantly lowered adhesion and invasiveness, while
PQS-treated PAO1 caused a significantly decreased survival time of mice with peritonitis (P<0.01). Farnesol treatment did not
obviously affected ExsA transcription (P>0.05) but caused a significant reduction in the transcriptional level of Exos (P<0.05) in
PAO1. PQS showed no significant effect on the adhesion and invasiveness of PAO1 (P>0.05). Conclusion PQS can maintain the
adhesion and invasiveness of Pseudomonas aeruginosa, and in the hosts of the bacteria, PQS concentration is positively
correlated with pyocyanin production and hence negatively with the survival time of the hosts.