Abstract
A novel strategy for combating pathogens is through the ongoing development and use of anti-quorum sensing (QS) treatments such as therapeutic bacteria or their anti-QS substances. Relatively little is known about the bacteria that inhabit the open ocean and of their potential anti-pathogenic attributes; thus, in an initiative to identify these types of therapeutic bacteria, planktonic microbes from the North Atlantic Ocean were collected, isolated, cultured and screened for anti-QS activity. Screening analysis identified one such strain, Rhizobium sp. NAO1. Extracts of Rhizobium sp. NAO1 were identified via ultra-performance liquid chromatography (UPLC) analysis. They were shown to contain N-acyl homoserine lactone (AHL)-based QS analogues (in particular, the N-butyryl homoserine lactone (C4-AHL) analogue) and could disrupt biofilm formation by Pseudomonas aeruginosa PAO1. QS inhibition was confirmed using confocal scanning laser microscopy and growth curves, and it was shown to occur in a dose-dependent manner without affecting bacterial growth. Secondary metabolites of Rhizobium sp. NAO1 inhibited PAO1 pathogenicity by downregulating AHL-mediated virulence factors such as elastase activity and siderophore production. Furthermore, as a result of biofilm structure damage, the secondary metabolite products of Rhizobium sp. NAO1 significantly increased the sensitivity of PAO1 to aminoglycoside antibiotics. Our results demonstrated that Rhizobium sp. strain NAO1 has the ability to disrupt P. aeruginosa PAO1 biofilm architecture, in addition to attenuating P. aeruginosa PAO1 virulence factor production and pathogenicity. Therefore, the newly identified ocean-derived Rhizobium sp. NAO1 has the potential to serve as a QS inhibitor and may be a new microbial resource for drug development.
Highlights
Biofilms are microbial communities contained within a matrix of extracellular polymeric substances (EPS) [1]
We found that addition of QS inhibitor (QSI) cell culture (50 μl), QSI supernatant (1%, 3% and 5%), aqueous extract (5%) or organic extract (0.5%) to PAO1 reduced biofilm formation by 32.0% (QSI), 65.1%, 72.3% and 75.9%, 77.9% and 72.3%
The results indicated that N-acyl homoserine lactone (AHL) analogues secreted by Rhizobium sp
Summary
Biofilms are microbial communities contained within a matrix of extracellular polymeric substances (EPS) [1]. Pathogens have developed a significant resistance to antibiotics, creating a critical need for alternative antimicrobial targets and novel therapeutic methods One such alternative antimicrobial target is quorum sensing (QS), which is a signalling mechanism that allows communication between bacteria and that can regulate the density, toxin production and motility of a microbial population using chemical signalling molecules such as auto-inducers [3,4,5,6]. This strategy is neither bactericidal (it does not kill bacteria) nor bacteriostatic (it does not inhibit bacterial growth) It appears to be a attractive alternative to other treatments because it does not impose a strong selective pressure, and bacterial resistance is less likely to develop. A strategy known as QS inhibition has been developed, for which an efficient screening for QS inhibitor (QSI) agents is required
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