Different effects of sub-minimum inhibitory concentrations of gentamicin on the expression of genes involved in alginate production and biofilm formation of .

BACKGROUND AND OBJECTIVES

Antibiotics at sub-minimum inhibitory concentrations (sub-MIC) may alter bacterial virulence factors. The objective of this study was to investigate the effect of gentamicin at sub-MIC concentrations on the expression of genes involved in alginate production and biofilm formation of

MATERIALS AND METHODS

The broth microdilution method was used to determine the MIC of gentamicin for three clinical isolates (P1-P3) and standard strains (PAO1 and 8821M). Alginate production and biofilm formation of the bacteria in the presence and absence of sub-MIC concentrations of gentamicin were measured using microtiter plate and carbazole assay, respectively. The real-time PCR method was used to determine the effect of gentamicin at sub-MIC concentrations on the expression level of genes involved in biofilm formation (A and A) and alginate production (D and U).

RESULTS

Gentamicin at sub-MIC concentrations significantly reduced alginate production, biofilm formation, and the expression of alginate and biofilm-encoding genes in clinical isolate P1. This inhibitory effect was also observed on the alginate production of 8821M strain and biofilm formation of PAO1strain. In clinical isolates, P2 and P3, alginate production, biofilm formation, and the expression of alginate and biofilm-encoding genes were significantly increased in exposure to sub-MIC concentrations of gentamicin.

CONCLUSION

This study showed that different phenotypic changes in clinical isolates and standard strains of in exposure to sub-MIC concentrations of gentamicin are associated with changes in the expression of virulence genes. Further researches are required to understand the mechanisms involved in regulating the expression of virulence genes after exposure to sub-MIC concentrations of antibiotics.