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.

Fluorescent carbon dots (N-CDs) were synthesized from ascorbic acid and urea following a green route and were characterized on the basis of analytical, spectroscopic, and microscopic techniques. The surface functional groups of the carbon dots were identified as −NH, −OH, CO, etc. using FT-IR. The N-CDs are highly stable under the wide ranges of pH, ionic strength, and solvents. It also exhibited an excitation wavelength dependent fluorescence property: the emission band with maximum intensity was observed at 415 nm by excitation at 340 nm. The metal ion sensing study revealed that N-CD detects Hg 2+ and Cu 2+ in aqueous media out of a large number of metal ions tested. A detailed study suggested that the metal ions interact with the surface bound functional groups of the multiple N-CDs, promoting aggregation, as evident from the TEM images, and quenching in emission intensity takes place through a PET process. For field application, paper-based sensing strips were prepared by coating N-CDs on filter paper, which was successfully tested for sensing of Hg 2+ and Cu 2+ in aqueous media as well as in solid state. N-CD was found to be nontoxic and was used as bioimaging agent for detection of Hg 2+ and Cu 2+ ions in the gastrointestinal tract of brine shrimp, Artemia.

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...

Aims:  To develop an effective multiplex PCR for simultaneous and rapid detection of Vibrio cholerae, Vibrio vulnificus and Vibrio parahaemolyticus, the three most important Vibrio species that can cause devastating health hazards among human. Methods and Results:  Species‐specific PCR primers were designed based on toxR gene for V. cholerae and V. parahaemolyticus, and vvhA gene for V. vulnificus. The multiplex PCR was validated with 488 Vibrio strains including 322 V. cholerae, 12 V. vulnificus, and 82 V. parahaemolyticus, 20 other Vibrio species and 17 other bacterial species associated with human diseases. It could detect the three target bacteria without any ambiguity even among closely related species. It showed good efficiency in detection of co‐existing target species in the same sample. The detection limit of all the target species was ten cells per PCR tube. Conclusions:  Specificity and sensitivity of the multiplex PCR is 100% each and sufficient for simultaneous detection of these potentially pathogenic Vibrio species in clinical and environmental samples. Significance and Impact of the Study:  This simple, rapid and cost‐effective method can be applicable in a prediction system to prevent disease outbreak by these Vibrio species and can be considered as an effective tool for both epidemiologist and ecologist.