Diallyl disulfide from garlic oil inhibits Pseudomonas aeruginosa virulence factors by inactivating key quorum sensing genes
Garlic oil can disrupt the quorum sensing (QS) pathways of the opportunistic pathogen Pseudomonas aeruginosa; however, the underlying mechanisms for this effect are unclear. Diallyl disulfide (DADS) is one of the most abundant sulfur-containing compounds in garlic oil. This study investigated the effects of DADS on the growth, virulence factor production (elastase, pyocyanin, biofilm, and swarming motility), and essential gene expression of P. aeruginosa PAO1, particularly as they apply to QS and virulence. DADS at 1.28 mg/mL did not affect P. aeruginosa PAO1 growth, although it decreased elastase and pyocyanin production, biofilm formation, and swarming motility. Each of these phenomena is regulated by the three QS systems of P. aeruginosa PAO1 (las, rhl, and pqs). Real-time q-PCR revealed that DADS down-regulated the transcription levels of several important QS genes (lasI, lasR, rhlI, rhlR, pqsA, and pqsR) in the three systems. Furthermore, the transcription levels of QS-regulated virulence genes were also down-regulated. The lasB gene, encoding LasB elastase, is co-regulated by the las, rhl, and pqs systems, and thus the down-regulation of genes across the three systems further down-regulated lasB. Additionally, phzM (encoding pyocyanin), pslB (responsible for the production of a biofilm matrix polysaccharide), and chiC (encoding chitinase) were positively activated by LasR, and a decrease in lasR transcription further down-regulated the transcription of phzM, pslB, and chiC. Hence, DADS inhibits P. aeruginosa PAO1 virulence factors by inactivating the transcription of key genes across three different QS systems.
KeywordsDiallyl disulfide Garlic oil Pseudomonas aeruginosa PAO1 Virulence factors
We thank Professor Zhang Lixin and Dai Huanqin of the CAS Key Laboratory of Pathogenic Microbiology and Immunology, Beijing, China, for their presenting strains of P. aeruginosa PAO1. We are obliged to the anonymous reviewers of Applied Microbiology and Biotechnology for their constructive comments.
This study was supported by grants from the Nature Science of Foundation of China (no. 31500113), Guangdong Provincial Nature Science of Foundation (no. 2016A030313800), Guangzhou Municipal Science and Technology Research Project (no. 201607020020), and Guangdong Provincial Science and Technology Project (no. 2013B010102014).
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Conflict of interest
The authors declare that they have no conflict of interest.
This manuscript represents original research performed by our group. It has not been submitted elsewhere, and it is not under consideration in any other journal. This article does not contain any studies with human participants or animals performed by any of the authors. All the authors have seen the manuscript and approved its submission to Applied Microbiology and Biotechnology.
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