Pseudomonas aeruginosa is one of the most studied bacteria in examining quorum sensing (QS) systems. In this study, gentamicin intermediate standard ATCC 27853 (GOS) strain and two clinical P. aeruginosa strains (one was susceptible and the other was intermediate; GD, GO) were compared according to biofilm and QS responses in minimum inhibitory concentrations (MIC) of gentamicin.

Gentamicin susceptibilities of these strains were studied according to Clinical Laboratory Standards Institute (CLSI) microdilution technique. MICs of gentamicin for intermediate and standard ATCC 27853 strains were found to be 4 μg / mL and for susceptible strain 0.25 μg / mL.

QS responses were evaluted by well diffusion and micro N- acyl-homoserine lactone (AHL) methods; short chain AHL(LasI/R) release that was signed by Choromobacteriun violaceum was not shown in gentamicin susceptible strain. But it was shown in gentamicin susceptible standard strain and intermediate clinical strains. Long chain AHL (RhlI/R) release by Agrobacterium tumefaciens was not demonstrated in GOS but was shown in GO and GD strains. Different QS responses were responsible in all strains isolated from wound and in standard strain isolated from blood culture in all MIC and sub- MIC values of gentamicin.

As a result of, we may suggest that QS responses may differ phenotypically, instead of being isolated from similar infection sites. In the future, phenotypic QS properties of Pseudomonas may take an important part in antibiotic development studies.