Weihua Chu

Effect of oral immunization with Aeromonas hydrophila ghosts on protection against experimental fish infection

Aims:  To investigate whether oral immunization with Aeromonas hydrophila ghosts (AHG) vaccine can elicit mucosal and systemic immune responses of Carp (Carassius auratus gibelio) compared to conventional formalin‐killed bacteria (FKC).

Quorum quenching bacteria Bacillus sp. QSI-1 protect zebrafish (Danio rerio) from Aeromonas hydrophila infection

Quorum Sensing (QS) is a bacterial regulatory mechanism, which is responsible for controlling the expression of various biological macromolecules such as the virulence factors in a cell density-dependent manner. Disruption of the QS system of pathogens has been proposed as a new anti-infective strategy. Biodegradation of AHLs proves to be an efficient way to interrupt QS, since AHLs are the main family of QS autoinducers used in Gram negative bacteria. In this study, the effect of Bacillus sp. QSI-1 as an efficient quorum quencher on virulence factors production and biofilm formation of fish pathogen Aeromonas hydrophila was investigated. QSI-1 reduced the accumulation of AHLs but did not affect the growth of A. hydrophila YJ-1 when cocultured. In the result, the supernatant of QSI-1 showed significant inhibition of protease production (83.9%), hemolytic activity (77.6%) and biofilm formation (77.3%) in YJ-1. In biocontrol experiment, QSI-1 significantly reduced the pathogenicity of A. hydrophila strain YJ-1 in zebrafish (Danio rerio). The fish fed with QSI-1 was observed to have a relative percentage survival of 80.8%. Our results indicate that AHLs degrading bacteria should be considered as an alternative for antibiotics in aquaculture for the biocontrol of bacterial fish diseases.

Corrigendum: Tea polyphenols as an antivirulence compound Disrupt Quorum-Sensing Regulated Pathogenicity of Pseudomonas aeruginosa.

Green tea, a water extract of non-fermented leaves of Camellia sinensis L., is one of the nonalcoholic beverages in China. It is becoming increasingly popular worldwide, because of its refreshing, mild stimulant and medicinal properties. Here we examined the quorum sensing inhibitory potentials of tea polyphenols (TP) as antivirulence compounds both in vitro and in vivo. Biosensor assay data suggested minimum inhibitory concentrations (MICs) of TP against selected pathogens were 6.25 ~ 12.5 mg/mL. At sub-MIC, TP can specifically inhibit the production of violacein in Chromobacterium violaceum 12472 with almost 98% reduction at 3.125 mg/mL without affecting its growth rate. Moreover, TP exhibited inhibitory effects on virulence phenotypes regulated by QS in Pseudomonas aeruginosa. The total proteolytic activity, elastase, swarming motility and biofilm formation were reduced in a concentration-dependent manner. In vivo, TP treatment resulted in the reduction of P. aeruginosa pathogenicity in Caenorhabditis elegans. When its concentration was 3.125 mg/mL, the survival rate reached 63.3%. In the excision wound infection model, the wound contraction percentage in treatment groups was relatively increased and the colony-forming units (CFU) in the wound area were significantly decreased. These results suggested that TP could be developed as a novel non-antibiotic QS inhibitor without killing the bacteria but as an antivirulence compound to control bacterial infection.

Characterization of N-Acyl-homoserine Lactones (AHLs)-Deficient Clinical Isolates of Pseudomonas aeruginosa

Abstract:Pseudomonas aeruginosa is an opportunistic pathogen causing severe respiratory infections. Acylated homoserine lactones (AHLs) are self-generated diffusible signal molecules that mediate population density dependent gene expression (quorum sensing, QS) in a variety of Gram-negative bacteria, and several virulence genes of bacterial pathogens are known to be controlled by QS. Hence, fitness mutant of virulent factors is beneficial for natural selection. In this study, strains of P. aeruginosa isolated from chronic lung infection of cystic fibrosis patients, were screened for AHLs production by using indicator strains of Chromobacterium violaceum CV026 and Agrobacterium tumefaciens strain At136. Four AHLs defective strains were selected from fifty-three clinical isolates. PCR analysis revealed that only one isolate was negative for lasR gene. These four AHLs defective isolates produced less virulence factors and forming less biofilm than PAO1. Only isolate PA41 produce little more pyocyanin than PAO1. The results indicate that, despite the pivotal role of QS in the pathogenesis of P. aeruginosa infections, AHLs-deficient strains are still capable of causing infections in human.

Effect of Traditional Chinese Herbal Medicine with Antiquorum Sensing Activity on Pseudomonas aeruginosa

Traditional Chinese herbal medicines (TCHMs) were tested for their ability of antiquorum sensing. Water extracts of Rhubarb, Fructus gardeniae, and Andrographis paniculata show antiquorumsensing activity when using Chromobacterium violaceum CV12472 as reporter; the sub-MIC concentrations of these TCHMs were tested against AHL-dependent phenotypic expressions of PAO1. Results showed significant reduction in pyocyanin pigment, protease, elastase production, and biofilm formation in PAO1 without inhibiting the bacterial growth, revealing that the QSI by the extracts is not related to static or killing effects on the bacteria. The results indicate a potential modulation of bacterial cell-cell communication, P. aeruginosa biofilm, and virulence factors by traditional Chinese herbal medicine. This study introduces not only a new mode of action for traditional Chinese herbal medicines, but also a potential new therapeutic direction for the treatment of bacterial infections, which have QSI activity and might be important in reducing virulence and pathogenicity of pathogenic bacteria.

Role of the quorum-sensing system in biofilm formation and virulence of Aeromonas hydrophila

Aeromonas hydrophila is a pathogen that causes disease in a wide range of homeothermic and poikilothermic hosts due to its multifactorial virulence. The production of many of these virulence determinants is associated with high cell density, a phenomenon that might be regulated by quorum sensing. The quorum sensing system regulates the expression of several virulence factors in a wide variety of pathogenic bacteria. To investigate the pathogenic role of quorum sensing system in A. hydrophila, We constructed an ahyI mutant strain of a fish-clinical isolate YJ-1, named YJ-1∆AhyI. Compared with the wild-type strain, the ahyI mutant strain exhibited a significant decrease of total extracellular virulent activity, and decreased in biofilm formation, intraperitoneal LD50 of YJ-1∆AhyI were more than 10 9 CFU, about 10 4 times higher than the parent strain. These results suggest that A.

Quorum Sensing Systems in Aeromonas spp.

Quorum sensing (QS) is an intercellular communication system by which bacterial cells are capable of indirectly monitoring their own population density through production and exchange of diffusible signal molecules. This enables bacteria to control gene expression dependent on population size and thereby perform coordinated phenotypic changes in a multicellular fashion. At present, QS regulatory systems have been reported for Gram-positive and Gram-negative bacteria. These systems rely on two major components, a small diffusible signalling molecule which accumulates in a population density-dependent manner and a transcriptional activator protein which, in concert with the signalling molecule, activates the expression of relevant genes. For Gram negatives, they employ N-acyl homoserine lactones (acyl HLs, AHLs) as the signalling molecule. AHL synthase encoded by LuxI homolog synthesizes AHL molecules. Short side-chain AHLs diffuse freely across cell membranes, whereas long side-chain AHLs have to use active efflux to partition to the membrane (Pearson et al. 1999). Upon reaching a threshold concentration in the extracellular medium, AHL molecules are perceived by cytoplasmic LuxR family proteins to regulate the downstream processes (Parsek and Greenberg 2000). As a consequence, expression of certain functions, often virulence factors required for pathogenesis, is triggered at high population densities in a coordinated manner.