RESUMEN
Quorum-sensing systems regulate expression of several virulence factors in Pseudomonas aeruginosa. This study investigated the relation between expression of the las quorum-sensing system and expression of mexY and ampC in 35 clinical isolates of P. aeruginosa. Antibiotic susceptibility was determined by the disc diffusion method according to the Clinical and Laboratory Standards Institute [CLSI] guidelines. Expression of genes including lasl, lasR, mexY, ampC and ampR was assessed by real time RT-PCR. Twenty eight isolates with elevated expression of mexY and ampC [compared to P. aeruginosa PAO1] were resistance to ceftazidime, imipenem, ciprofloxacin and amikacin. Also these isolates demonstrated increased expression of lasl and lasR. The remaining seven isolates showed intermediate resistance to ciprofloxacin and amikacin. These seven isolates with elevated ampR expression -demonstrated decreased expression of mex Y, ampC, lasl and lasR. In contrast to previous study, current study demonstrated that the expression pattern of ampC was identical to the lasl expression pattern among clinical isolates. Furthermore according to previous study we expected that AmpR positively regulated ampC expression but in our study, some of the isolates with elevated ampR expression showed decreased ampC expression. The expression pattern of lasR and mexYwas identical in all of the isolates. It seems there was a direct or indirect relation between expression of lasR and mexY expression in P. aeruginosa