e Proteases in Vibrio cholerae have been shown to play a role in its pathogenesis. V. cholerae secretes Zn-dependent hemagglutinin protease (HAP) and calcium-dependent trypsin-like serine protease (VesC) by using the type II secretion system (TIISS). Our present studies demonstrated that these proteases are also secreted in association with outer membrane vesicles (OMVs) and transported to human intestinal epithelial cells in an active form. OMV-associated HAP induces dose-dependent apoptosis in Int407 cells and an enterotoxic response in the mouse ileal loop (MIL) assay, whereas OMV-associated VesC showed a hemorrhagic fluid response in the MIL assay, necrosis in Int407 cells, and an increased interleukin-8 (IL-8) response in T84 cells, which were significantly reduced in OMVs from VesC mutant strain. Our results also showed that serine protease VesC plays a role in intestinal colonization of V. cholerae strains in adult mice. In conclusion, our study shows that V. cholerae OMVs secrete biologically active proteases which may play a role in cytotoxic and inflammatory responses. Vibrio cholerae is the causative agent of the life-threatening disease cholera. Cholera epidemics in Haiti in 2010 provide evidence that it still remains an ongoing public health threat (1). Strains of the El Tor biotype O1 serogroup are responsible for seventh pandemic and recent cholera outbreaks (2). Cholera toxin (CT) and toxin-coregulated pilus (TCP) have been identified as the major virulence factors for V. cholerae pathogenesis. CT is responsible for profuse watery diarrhea, whereas TCP is essential for sustaining colonization of human small intestine. V. cholerae also secretes several proteases which may also play a role in its pathogenesis (3).The major protease secreted by V. cholerae strains is the 35-kDa hemagglutinin protease (HAP) (4). HAP has been reported to accelerate the bacterial detachment from cultured cells by digestion of V. cholerae adhesins (5). HAP modulates the enterotoxigenicity of cholera toxin by nicking the A subunit of CT (6). HAP also plays a role in processing hemolysin to its mature form by removal of a 15-kDa N-terminal peptide (7). As shown in the above-mentioned studies, HAP plays an indirect role in V. cholerae pathogenesis. The possibility of its direct role in pathogenesis has been shown by Ghosh et al. (8). They reported that purified HAP from a V. cholerae non-O1, non-O139 strain showed a hemorrhagic response in rabbit ileal loops (RILs) and an increase in intestinal short-circuit current in Ussing's chamber (8). Besides HAP, the other major well-characterized metalloprotease is a 97-kDa Vibrio cholerae protease, PrtV which has been shown to play a role in virulence in the Caenorhabditis elegans infection model (9). In an earlier study, we also reported the presence of a novel serine protease encoded by VC1649 (VesC) in a hapA prtV mutant Vibrio cholerae O1 strain and showed its role in the hemorrhagic response in the rabbit ileal loop model (10).Gram-negative bacteria, including V. cholerae, us...

bThe severe diarrheal disease cholera is endemic in over 50 countries. Current therapies for cholera patients involve oral and/or intravenous rehydration, often combined with the use of antibiotics to shorten the duration and intensity of the disease. However, as antibiotic resistance increases, treatment options will become limited. Linoleic acid has been shown to be a potent negative effector of V. cholerae virulence that acts on the major virulence transcription regulator protein, ToxT, to inhibit virulence gene expression. ToxT activates transcription of the two major virulence factors required for disease, cholera toxin (CT) and toxin-coregulated pilus (TCP). A conjugated form of linoleic acid (CLA) is currently sold over the counter as a dietary supplement and is generally recognized as safe by the U.S. Food and Drug Administration. This study examined whether CLA could be used as a new therapy to reduce CT production, which, in turn, would decrease disease duration and intensity in cholera patients. CLA could be used in place of traditional antibiotics and would be very unlikely to generate resistance, as it affects only virulence factor production and not bacterial growth or survival.

Like most other Gram‐negative bacteria, Shigella releases outer membrane vesicles (OMVs) into the surrounding environment during growth. In this study, we have exploited OMVs of Shigella as a protective immunogen in a mice model against Shigellosis. Distinctive vesicle secretion was noticed from different Shigella strains. Among them, Shigella boydii type 4 (BCH612) was secreting relatively higher amounts. We immunized female adult mice orally with 32 μg of purified Shigella boydii type 4 (BCH612) OMVs four times at 1‐week intervals. Antibodies against these vesicles were detected in immunized sera until 120 days, indicating a persistent immune response. To observe whether the passive immunity had been transferred to the neonates, the immunized female mice were mated and the offspring were challenged orally, with wild‐type homologous and heterologous Shigella strains. All offspring of immunized mothers survived the challenge with homologous strain BCH612 and up to 81% protective efficacy was noted against heterologous strains Shigella dysenteriae 1, Shigella flexneri 2a, Shigella flexneri 3a, Shigella flexneri 6 and Shigella sonnei. Our results exhibited for the first time that oral immunization of adult female mice with purified OMVs of Shigella, without any adjuvant, conferred passive protection to their offspring against shigellosis. These findings will contribute to the future development of a potential non‐living vaccine candidate against shigellosis.

Vibrio cholera survival in an aquatic environment depends on chitin utilization pathway that requires two factors, chitin binding protein and chitinases. The chitinases and the chitin utilization pathway are regulated by a two-component sensor histidine kinase ChiS in V. cholerae. In recent studies these two factors are also shown to be involved in V. cholerae pathogenesis. However, the role played by their upstream regulator ChiS in pathogenesis is yet to be known. In this study, we investigated the activation of ChiS in presence of mucin and its functional role in pathogenesis. We found ChiS is activated in mucin supplemented media. The isogenic chiS mutant (ChiS) showed less growth compared to the wild type strain (ChiS) in the presence of mucin supplemented media. The ChiS strain also showed highly retarded motility as well as mucin layer penetration in vitro. Our result also showed that ChiS was important for adherence and survival in HT-29 cell. These observations indicate that ChiS is activated in presence of intestinal mucin and subsequently switch on the chitin utilization pathway. In animal models, our results also supported the in vitro observation. We found reduced fluid accumulation and colonization during infection with ChiS strain. We also found ChiS mutant with reduced expression of ctxA, toxT and tcpA. The cumulative effect of these events made V. cholerae ChiS strain hypovirulent. Hence, we propose that ChiS plays a vital role in V. cholerae pathogenesis.

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