Acinetobacter species remain alive in hospitals on various surfaces, both dry and moist, forming an important source of hospital infections. These bacteria are naturally resistant to many antibiotic classes. Although the role of the quorum sensing system in regulating the virulence factors of Acinetobacter species has not been fully elucidated, it has been reported that they play a role in bacterial biofilm formation. The biofilm formation helps them to survive under unfavorable growth conditions and antimicrobial treatments. It is based on the accumulation of bacterial communication signal molecules in the area. In this study, we compared the bacterial signal molecules of 50 nosocomial Acinetobacter baumannii strain and 20 A. baumannii strain isolated from soil. The signal molecules were detected by the biosensor bacteria (Chromobacterium violaceum 026, Agrobacterium tumefaciens A136, and Agrobacterium tumefaciens NTL1) and their separation was determined by thin-layer chromatography. As a result, it has been found that soil-borne isolates can produce 3-oxo-C8-AHL and C8-AHL, whereas nosocomial-derived isolates can produce long-chain signals such as C10-AHL, C12-AHL, C14-AHL and C16-AHL. According to these results, it is possible to understand that these signal molecules are found in the infection caused by A. baumannii. The inhibition of this signaling molecules in a communication could use to prevent multiple antibiotic resistance of these bacteria.

Quorum sensing (QS) and biofilm formation are important mechanisms related to antibiotic resistance of many pathogens. Alternative treatments are needed to prevent recurrent or chronic infections caused by multi-resistant pathogens. Therefore, the aim of this study is to investigate and compare the inhibitory potential of the dietary phytochemicals: curcumin, quercetin, apigenin, pyrogallol, gallic acid and luteolin against QS of and biofilm formation by Chromobacterium violaceum ATCC 12472 and the swimming and swarming abilities of Pseudomonas aeruginosa PAO1. Anti-QS potential of the phytochemicals was evaluated qualitatively and quantitatively using C. violaceum via the disk diffusion assay based on violacein pigment inhibition at the subminimal inhibitory concentrations ranging from 46.87 to 750 µg/mL. The results of anti-QS and antibiofilm activities on C. violaceum demonstrated that all the phytochemicals except pyrogallol and gallic acid inhibited violacein production (from (11.0±0.1) to (88.2±0.1) %) in a concentration-dependent manner. In addition, the biofilm formation was also significantly inhibited (p<0.05) in the presence of all the phytochemicals ((1.38±0.08)–(84.2±0.2) %). In the present study, the results revealed that quercetin, curcumin, apigenin and luteolin could be promising QS and biofilm inhibitory agents against the C. violaceum 12472 biosensor system. Our findings also suggest that all the phytochemicals, especially curcumin, quercetin and pyrogallol, might be anti-pathogenic agents against P. aeruginosa PAO1 infections due to the ability to control QS. However, more comprehensive studies at the molecular level, explaining their anti-QS mechanisms, need to be conducted to confirm these results and identify the genes involved.

Quorum sensing system plays an active role in the regulation of pathogenicity of many microorganisms. Inhibition of pathogenicity or virulence factors will increase the success of treatment by preventing the development of antibiotic resistance. In this study, anti-quorum sensing activities of quercetin and resveratrol compounds, which have antioxidant property without damaging to host, have been determined via using biosensor bacteria: Chromobacterium violaceum ATCC 12472 and Chromobacterium violaceum CV026. As quorum sensing inhibitors, quercetin and resveratrol's cutting off the bacterial communication will prevent the treatment failures caused by the development of bacterial resistance. The development of layered drugs with antioxidant compounds such as quercetin and resveratrol will pave the way for new horizons for new therapeutic strategies.

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