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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.

Aims:  This work was aimed at identifying strains which can degrade quorum‐sensing (QS) molecules from fish gut, with properties suitable for use as probiotic in aquaculture. Methods and Results:  A total of 200 strains were obtained from the intestine gut of Carassius auratus gibelio after enrichment in KG medium contained 500 μg l−1 of C6‐HSL as the sole source of carbon and nitrogen; one strain named QS inhibitor (QSI)‐1 was identified as the genus Bacillus spp. by morphological phenotypes, and the strain also possessed an aiiA homologue gene using PCR amplification. In vitro, QSI‐1 strongly interfered with violacein production by Chromobacterium violaceum. Coculture of QSI‐1 with fish pathogen effectively reduced the amount of acyl‐homoserine lactones (AHLs) and the extracellular proteases activity of Aeromonas hydrophila YJ‐1. The oral LD50 of QSI‐1 to fish was more than 1011 CFU shown that it was avirulent to fish. Fish fed diet supplemented with QSI‐1 had good survival, suggesting that QSI‐1 showed protection against Aer. hydrophila infection. Conclusions:  The results indicate that the isolate QSI‐1 might have the potential possibility to be used as a probiotic in aquaculture. Significance and Impact of the Study:  This is the first report to describe a bacterium isolated from the intestine gut of C. auratus gibelio which can degrade AHLs and has the probiotic characteristics for its use in aquaculture.

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Fourteen strains of Bdellovibrio-like organisms were isolated from cultured fish ponds using Aeromonas hydrophila J-1 as host, one of them formed large plaques after 48 h of incubation at 28 degrees C on a double layer plate, designated as Bdellovibrio C-1. The Bdellovibrio was confirmed by electron microscopy and PCR amplification of Bdellovibrio-specific 16S rDNA. The optimum temperature for the growth of BdC-1 was between 15-37 degrees C and with optimal activity at temperatures of 25-30 degrees C. The ability of BdC-1 to lyse A. hydrophila was similar in the pH range of 6.5 to 8.5. It can lyse 23 Gram-negative bacterial strains comprising three genera of fish pathogens and one strain of Escherichia coli but cannot lyse Gram-positive bacteria such as Bacillus subtillis and Staphylococcus aureus. Immersion of fish in water containing different concentrations of BdC-1 was used in protection against an experimental infection of A. hydrophila J-1. Results show that the mortality of groups immersed with BdC-1 was lower than the group without BdC-1. These results suggest that it may be possible to use Bdellovibrio to control the disease caused by A. hydrophila.

Staphylococcus aureus causes a broad range of life-threatening diseases in humans. This bacterium produces a large number of extracellular virulence factors that are closely associated with specific diseases which are controlled by quorum sensing. In this study, we show that azithromycin was active against methicillin-resistant Staphylococcus aureus (MRSA) strains with MICs ranged from 32 to 64 lg/mL. Azithromycin at subinhibitory concentration, markedly reduced the production of a-hemolysin at (1/16MIC, 1/8MIC) and biofilm formation at (1/16MIC, 1/8MIC), respectively. The results indicated that sub-inhibitory concentrations of azithromycin decreased the production of a-hemolysin and biofilm formation in MRSA in a dose-dependent manner. Therefore, azithromycin may be useful in the treatment of a-hemolysin producing and biofilm formation MRSA infections.Staphylococcus aureus is found among the normal human skin flora and it is an important pathogen of humans, causing diseases ranging from superficial skin and wound infections to severe illnesses such as septicaemia, endocarditis and toxic shock syndrome [1]. S. aureus is particularly a problem in hospitals because it spreads easily in these environments and causes potentially fatal infections in immunocompromised hospital patients. S. aureus cause disease through the production of virulence factors. These factors include adhesins, exotoxins, enterotoxins, hemolysins, and leukocidin, as well as proteases that enable the bacteria to spread within the host [2,3]. Quorum sensing (QS) regulates expression of genes encoding these virulence factors and biofilm formation. Strains defective in their ability to form a biofilm or produce toxins show diminished virulence [4], suggesting that a novel approach for therapy development would be to interfere with the production of virulence factors [5][6][7]. Azithromycin (AZM) is one of the macrolides antibiotics, and it is a broad-spectrum macrolide antibiotic effective against Gram-positive, Gram-negative, and atypical bacteria and has anti-inflammatory characteristics [8]. The purpose of this study is to assess the effect of azithromycin, used as a quorum-sensing inhibitor, for decrease the production of QS associated virulence factors and biofilm formation in Staphylococcus aureus.Two different clinical bacterial strains of methicillinresistant Staphylococcus aureus (MRSA) 10 and 21 were collected from different patients hospitalized at Lishui People's Hospital, Zhejiang province. S. aureus strains was identified biochemically from routinely obtained specimens by means of the Vitek ATB Expression System, version 2.7.8 (BioMe'rieux Deutschland GmbH, Nürtin-gen, Germany), which uses 32 biochemical reactions. Bacterial isolates were stored as suspensions in LB medium containing 12.5 % (vol/vol) glycerol at -70°C until tests were performed. S. aureus MRSA 10, 21 single colony was inoculated into LB media and cultured overnight at 37. Overnight culture was subcultured (1:100) into test tubes with fresh LB medium in tripl...

Abstract-This paper studies maximum multiflow (MMF) and maximum concurrent multiflow (MCMF) in muliti-channel multi-radio multihop wireless networks under the 802.11 interference model or the protocol interference model. We introduce a fine-grained network representation of multi-channel multi-radio multihop wireless networks and present some essential topological properties of its associated conflict graph. By exploiting these properties, we develop practical polynomial approximation algorithms for MMF and MCMF with constant approximation bounds regardless of the number of channels and radios. Under the 802.11 interference model, their approximation bounds are at most 20 in general and at most 8 with uniform interference radii; under the protocol interference model, if the interference radius of each node is at least times its communication radius, their approximation bounds are at most 2 (⌈ / arcsin) . In addition, we also prove that if the number of channels is bounded by a constant (which is typical in practical networks), both MMF and MCMF admit a polynomial-time approximation scheme under the 802.11 interference model or under the protocol interference model with some additional mild conditions.