different effects of subinhibitory concentrations of gentamicin on expression of alginate and biofilm genes of Pseudomonas aeruginosa clinical isolates

Background and Aim : P. aeruginosa is an important opportunistic pathogen and major cause of nosocomial infections. Alginate production and biofilm formation have important roles in pathogenesis of P. aeruginosa infections. Antibiotics at subinhibitory concentrations (sub-MIC) may affect P. aeruginosa virulence factors. The purpose of this study was to investigate the effects of gentamicin at sub-MIC concentrations on alginate production, biofilm formation and expression of their specific genes in P. aeruginosa standard strains and clinical isolates.Methods : The minimum inhibitory concentration of gentamicin was determined by microdilution broth method against ۳ clinical isolates of P. aeruginosa (P۱-P۳) and standard strains (PAO۱ & ۸۸۲۱M). In each of P. aeruginosa clinical isolates and standard strains, the effects of gentamicin at ۱/۲MIC and ۱/۴MIC concentrations on expression level of alginate genes (algD, algU) and biofilm genes (pelA , pslA) were determined using Real-Time PCR method. The effects of these concentrations on alginate production and biofilm formation were evaluated using microtiter plate and carbazole assay, respectively.Results : Gentamicin at sub-MIC concentrations reduced expression of algD, algU, pelA and pslA genes, biofilm formation and alginate production in P. aeruginosa clinical isolate P۱. This inhibitory effect was also observed on alginate production and biofilm formation of standard strains ۸۸۲۱M and PAO۱, respectively. However, exposure with sub-MIC concentrations of gentamicin increased alginate production, biofilm formation and expression of their specific genes in P. aeruginosa clinical isolatesP۲ and P۳.Conclusion : This study showed that Gentamicin at sub-MIC concentrations affect the expression of alginate and biofilm specific genes and subsequently causes different changes in alginate production and biofilm formation of P. aeruginosa clinical isolates and standard strains. Further studies should be conducted to understand the regulation of virulence genes expression in the presence of sub-MIC concentrations of antibiotics.

کلیدواژه ها:

Alginate ، Biofilm ، Gentamicin ، Pseudomonas aeruginosa