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.

Cytolethal distending toxins (CDTs) are inhibitory cyclomodulins, which block eukaryotic cell proliferation and are produced by a diverse group of Gram-negative bacteria, including Escherichia coli strains associated with intestinal and extraintestinal infections. However, the mode of transmission of the toxin gene clusters among diverse bacterial pathogens is unclear. We found that Cdt-I produced by enteropathogenic E. coli strains associated with diarrhea is encoded by a lambdoid prophage, which is inducible and infectious. The genome of Cdt-I converting phage (CDT-1⌽) comprises 47,021 nucleotides with 60 predicted ORFs organized into six genomic regions encoding the head and tail, virulence, integrase, unknown functions, regulation, and lysis. The genomic organization of CDT-1⌽ is similar to those of SfV, a serotype-converting phage of Shigella flexneri, and UTI89, a prophage identified in uropathogenic E. coli. Besides the cdtI gene cluster, the virulence region of CDT-1⌽ genome contains sequences homologous to a truncated cycle inhibiting factor and a type 3 effector protein. Mutation analysis of susceptible E. coli strain C600 suggested that the outer membrane protein OmpC is a putative receptor for CDT-1⌽. CDT-1⌽ genome was also found to integrate into the host bacterial chromosome forming lysogens, which produced biologically active Cdt-I. Furthermore, phage induction appeared to cause enhanced toxigenicity of the E. coli strains carrying lysogenic CDT-1⌽. Our results suggest that CDT-1⌽ is the latest member of a growing family of lambdoid phages encoding bacterial cyclomodulins and that the phage may have a role in horizontal transfer of these virulence genes.bacterial genotoxin ͉ converting phage ͉ cyclomodulins

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...

ABSTRACT. Shiga toxin-producing Escherichia coli (STEC) isolated from Japan were investigated for the distribution of virulence genes. A total of 232 STEC strains including 171 from cattle and 61 from human were examined for the occurrence of genes responsible for bacterial adhesions to intestine, e.g., eae (intimin, E. coli attaching and effacing), saa (STEC autoagglutinating adhesin), iha (irgA homologue adhesin), efa1 (E. coli factor for adherence), lpfA O113 (long polar fimbriae), and ehaA (EHEC autotransporter) by colony hybridization assay. Similarly, the presence of toxigenic cdt (cytolethal distending toxin), and subAB (subtilase cytotoxin) genes were also checked. Among cattle isolates, 170, 163, 161, 155, 112 and 84 were positive for lpfA O113 (99%), ehaA (95%), iha (94%), saa (91%), subAB (65%), and cdt-V (49%), respectively, while 2 were positive for eae (1.2%) and efa1 (1.2%) each. In case of human isolates, 60, 59, 58 and 58 were positive for ehaA (98%), iha (97%), efa1 (95%), and eae (95%), respectively, while 11, 2, 2, and 1 were positive for lpfA O113 (18%), saa (3.3%), cdt-V (3.3%), and subAB (1.6%), respectively. Therefore, in human STEC isolates efa1 and eae whereas in cattle isolates saa, lpfA O113 , cdt-V and subAB were prevalent. These data indicate differential occurrence of some pathogenic genes in human and cattle originated STEC strains in Japan.