Quorum quenching activity of isolate 30b confers antipathogenic effects in .

Quorum quenching, the interference of a Quorum sensing (QS) system that contributes to the pathogenesis through triggering the production of various virulence determinants, is among the newly suggested antivirulence strategies. This study aimed at screening of N-Acyl homoserine lactonase activity from local bacterial isolate, and investigating its effect on () virulence and biofilm formation. Soil bacteria were screened for gene coding for lactonase enzyme by Polymerase Chain reaction and sequencing of gene homologs. Lactonase activity and spectrum were assessed in the cell-free lysate by well diffusion assay using KYC55. A bacterial isolate showing the highest N-acyl-homoserine lactones degradation percentage was identified by gene amplification and sequencing of the 16S rRNA gene and its gene homolog. High performance liquid chromatography was used to confirm N-acyl-homoserine lactone degradation. The effect of cell-free lysate on the biofilm formation ability and cytotoxicity of PAO1 and clinical isolates from different clinical sources were assessed by static microtiter plate and viability assay, respectively Lactonase gene and activity were identified in three spp. isolates. They showed broad catalytic activities against tested N-acyl-homoserine lactones. However, The lactonase activity in the cell- free lysate of isolate 30b showed the highest significant degradation percentage on all tested signals; N-butanoyl-L-homoserine lactone (71%), N-hexanoyl-l-homoserine lactone (100%), N-decanoyl-homoserine lactone (100%), N-(3-oxohexanoyl)-L-homoserine lactone (37.5%), N-(oxodecanoyl)-L-homoserine lactone (100%), and N-(3-oxododecanoyl)-L-homoserine lactone (100%). Alignment of the amino acid sequences of AiiA protein of isolate 30b showed 96% identity with () homologous lactonases in the GenBank database, and the isolate was designated as isolate 30b. Cell-free lysate of isolate 30b reduced biofilm formation significantly in 93% of isolates. The highest mean percentage of reduction in the biofilm was 86%. Moreover, the viability percentage of human lung carcinoma A549 cells infected by and treated with cell-free lysate of isolate 30b increased up to 15%. The results of this study highlight the potential of lactonases as a promising strategy to combat virulence.