Characterization of N-Acyl-homoserine Lactones (AHLs)-Deficient Clinical Isolates of Pseudomonas aeruginosa

Pseudomonas aeruginosa is an opportunistic pathogen causing severe respiratory infections. Acylated homoserine lactones (AHLs) are self-generated diffusible signal molecules that mediate population density dependent gene expression (quorum sensing, QS) in a variety of Gram-negative bacteria, and several virulence genes of bacterial pathogens are known to be controlled by QS. Hence, fitness mutant of virulent factors is beneficial for natural selection. In this study, strains of P. aeruginosa isolated from chronic lung infection of cystic fibrosis patients, were screened for AHLs production by using indicator strains of Chromobacterium violaceum CV026 and Agrobacterium tumefaciens strain At136. Four AHLs defective strains were selected from fifty-three clinical isolates. PCR analysis revealed that only one isolate was negative for lasR gene. These four AHLs defective isolates produced less virulence factors and forming less biofilm than PAO1. Only isolate PA41 produce little more pyocyanin than PAO1. The results indicate that, despite the pivotal role of QS in the pathogenesis of P. aeruginosa infections, AHLs-deficient strains are still capable of causing infections in human.