Co-regulation of β-lactam resistance, alginate production and quorum sensing in Pseudomonas aeruginosa

Abstract

Development ofβ-lactam resistance, production of alginate and modulation of virulence factor expression that alters host immune responses are the hallmarks of chronicPseudomonas aeruginosainfection in cystic fibrosis patients. In this study, we propose that a co-regulatory network exists between these mechanisms. We compared the promoter activities ofampR,algT/U,lasR,lasI,rhlR,rhlIandlasAgenes, representing theβ-lactam antibiotic resistance master regulatory gene, the alginate switch operon, thelasandrhlquorum-sensing (QS) genes, and the LasA staphylolytic protease, respectively. Four isogenicP. aeruginosastrains, the prototypic Alg−PAO1, Alg−PAOampR, the mucoid Alg+PAOmucA22(Alg+PDO300) and Alg+PAOmucA22ampR(Alg+PDOampR) were used. We found that in the presence of AmpR regulator andβ-lactam antibiotic, the extracytoplasmic function sigma factor AlgT/U positively regulated PampR, whereas AmpR negatively regulated PalgT/U. On the basis of this finding we suggest the presence of a negative feedback loop to limitalgT/Uexpression. In addition, the functional AlgT/U caused a significant decrease in the expression of QS genes, whereas loss ofampRonly resulted in increased PlasIand PlasRtranscription. The upregulation of thelasQS system is likely to be responsible for the increasedlasApromoter and the LasA protease activities in Alg−PAOampRand Alg+PDOampR. The enhanced expression of virulence factors in theampRstrains correlated with a higher rate ofCaenorhabditis elegansparalysis. Hence, this study shows that the loss ofampRresults in increased virulence, and is indicative of the existence of a co-regulatory network betweenβ-lactam resistance, alginate production, QS and virulence factor production, with AmpR playing a central role.