The use of natural compounds as inhibitory agents for virulence factor production is a new approach to overcome increased antimicrobial resistance in pathogenic bacteria. In this study, we examined whether red chilli (Capsicum annuum) contains any such compound(s) that can repress the cholera toxin (CT) production in Vibrio cholerae. We found that the methanol extract of red chilli could inhibit CT production in recently emerged V. cholerae O1 El Tor variant strains without affecting their viability. Interestingly, capsaicin, a well-studied active component of red chilli, also drastically inhibited CT production in V. cholerae strains belonging to various serogroups including variants. Real-time quantitative reverse transcription-PCR assay revealed that capsaicin effectively repressed the transcription of ctxA, tcpA and toxT genes, but not of toxR and toxS genes. On the contrary, capsaicin significantly enhanced the transcription of the hns gene, the product of which is known to regulate negatively the transcription of ctxAB, tcpA and toxT genes. These results suggest that capsaicin might act as a potent repressor for CT production possibly by enhancing the transcription of hns.

Vibrio cholerae O1 El Tor variant strains produced much more cholera toxin than did prototype El Tor strains. The amount of cholera toxin produced by El Tor variant strains both in vitro and in vivo was more or less equivalent to that produced by classical strains.

Shrimp diseases are frequently reported to be caused by closely related vibrios, and in many cases they are tentatively but inaccurately identified as Vibrio harveyi and related vibrios. In the present study, 28 biochemically identified V. harveyi-related strains isolated from diseased shrimps were randomly selected for further characterization by molecular tools. Twenty-six strains were identified as Vibrio campbellii and two as V. harveyi by sequence analysis of 16S rRNA and uridylate kinase genes. Haemolysin-gene-based species-specific multiplex PCR also confirmed these results. Experimental challenge studies using Artemia as a model showed that eight isolates were highly pathogenic, three were moderately pathogenic and the remaining 17 were non-pathogenic. Ribotyping with BglI clearly distinguished V. campbellii from V. harveyi, but it failed to separate pathogenic and non-pathogenic clusters. Artemia nauplii challenged with a fluorescently labelled highly pathogenic strain (IPEY54) showed patches in the digestive tract. However, no patches were observed for a non-pathogenic strain (IPEY41). Direct bacterial counts also supported colonization potential for the highly pathogenic strain. To our knowledge, this is the first report on the isolation and accurate identification of large numbers of V. campbellii associated with shrimp disease in aquacultural farms. V. campbellii has long been considered to be non-pathogenic and classified with V. harveyi-related bacteria. However, we show that this species may be an emerging aquaculture pathogen. This study will help to formulate suitable strategies to combat this newly identified pathogen. INTRODUCTIONHalophilic vibrios such as Vibrio harveyi are ubiquitous in the marine environment and are implicated as the causes of several diseases in wild and cultured aquatic organisms. Due to the plasticity of Vibrio genomes, with frequent horizontal gene transfer events, species boundaries are very narrow in the marine environment (Fraser et al., 2007). Hence, the identification of V. harveyi and related species isolated from the marine environment is sometimes difficult. Luminous vibrios including V. harveyi have been implicated principally with disease outbreaks in shrimp larval culture facilities and grow-out ponds worldwide. Due to the high level of phylogenetic similarity among marine vibrios, bacteria associated with disease outbreaks have often been misidentified. For example, although strain LMG 19703 T (or AK1 T ) showed 99.4 % sequence similarity in 16S rRNA with Vibrio mediterranei (ATCC 43341 T ), Kushmaro et al. (2001) initially classified it as a new species, Vibrio shiloi, due to large differences in phenotypic properties. Later, Thompson et al. (2001), on the basis of genotypic features such as fluorescent amplified fragment length polymorphism and DNA-DNA hybridization, as Abbreviations: ASW, artificial seawater; DOC, days of culture; DTAF, 5-(4,6-dichlorotriazin-2-yl)aminofluorescein; NJ, neighbour joining. The GenBank/EMBL/DDBJ accession numbers for the se...

A bacterial disease was reported from gilthead sea bream (Sparus aurata) within a hatchery environment in Malta. Symptoms included complete erosion of tail, infection in the eye, mucous secretion and frequent mortality. A total of 540 strains were initially isolated in marine agar from different infected body parts and culture water sources. Subsequently 100 isolates were randomly selected, identified biochemically and all were found to be Vibrio harveyi-related organisms; finally from 100 isolates a total of 13 numbers were randomly selected and accurately identified as V. harveyi by 16S rRNA gene sequencing and species-specific PCR. Ribotyping of these strains with HindIII revealed total of six clusters. In vivo challenge study with representative isolates from each cluster proved two clusters each were highly pathogenic, moderately pathogenic and non-pathogenic. All 13 isolates were positive for hemolysin gene, a potential virulence factor. Further analysis revealed probably a single copy of this gene was encoded in all isolates, although not in the same locus in the genome. Although V. harveyi was reported to be an important pathogen for many aquatic organisms, to our knowledge this might be the first report of disease caused by V. harveyi and their systematic study in the sea bream hatchery from Malta.

Dual functional activity by the same organic–inorganic hybrid material toward selective metal ion detection and its adsorption has drawn more attraction in the field of sensing. However, most of the hybrid materials in the literature are either for sensing studies or adsorption studies. In this manuscript, a fluorescent active hybrid material SiO2@PBATPA is synthesized by covalent coupling of anthracene‐based chelating ligand N,N′‐(propane‐1,3‐diyl) bis(N‐(anthracen‐9‐ylmethyl)‐2‐((3‐(triethoxysilyl)propyl) amino) acetamide) (PBATPA) within the mesopores of newly synthesized cubic mesoporous silica. The synthetic strategy is designed to form an exclusively intramolecular excimer on a solid surface, which is then used as a sensory tool for selective detection of metal ions through fluorescence quenching by the destruction of excimer upon metal ion binding. The dual functions of sensing and adsorption studies show selectivity toward Hg2+ and Cu2+ among various metal ions with detection limits of 37 and 6 ppb, respectively, and adsorption capacities of 482 and 246 mg g−1, respectively. This material can be used as a sensory cum adsorbent material in real food samples and living organisms such as the brine shrimp Artemia salina without any toxic effects from the material.