Kegg Pathway: Cholera - Life cycle

Vaccine. 2008 Jul 23; 26(31): 3913-21
Cong H, Gu QM, Yin HE, Wang JW, Zhao QL, Zhou HY, Li Y, Zhang JQ

The search for an effective vaccine against toxoplasmosis remains a challenging and elusive goal. Combination of epitopes from different stages of Toxoplasma gondii Life cycle is an optimal strategy to overcome the antigen complexity of the parasite. Based on published epitope derived from several promising candidate vaccine antigens, we construct a DNA vaccine encoding multi-epitope of T. gondii and CpG motif, with or without the A(2)/B subunit of Cholera toxin as a genetic adjuvant. The immunity induced by this vaccine in BALB/c mice and the protection afforded against challenge with the highly virulent RH strain of T. gondii is assessed. This vaccine was able to elicit a significant humoral and cellular immune response in vaccinated mice. Furthermore, CTXA(2)/B as a genetic adjuvant could enhance the magnitude of immune responses as well as increased survival rate in mice infected with the lethal RH tachyzoites. This study is the first report of a multi-epitope DNA construct strategy as a potential DNA vaccine against toxoplasmosis.

J Virol. 2008 Jun; 82(11): 5212-9
Medigeshi GR, Hirsch AJ, Streblow DN, Nikolich-Zugich J, Nelson JA

West Nile virus (WNV) has been the leading cause of viral encephalitis in the United States since 1999. The endocytic processes involved in the internalization of infectious WNV by various cell types are not well characterized, and the involvement of cholesterol-rich membrane microdomains, or lipid rafts, in the Life cycle of WNV has not been investigated previously. In this study, we found that the depletion of cellular cholesterol levels by brief treatment with methyl-beta-cyclodextrin resulted in a 100-fold reduction of the titers of infectious WNV released into the culture supernatant, as well as a reduction in the number of WNV genome copies in the cholesterol-depleted cells. The addition of exogenous cholesterol to cholesterol-depleted cells reversed this effect. Cholesterol depletion postinfection did not affect WNV growth, suggesting that the effect occurs at the level of WNV entry. We also showed that while WNV entry did not require alphavbeta3 integrin and focal adhesion kinase, WNV particles failed to be internalized by cholesterol-depleted cells. Finally, we showed the colocalization of the WNV envelope protein and Cholera toxin B, which is internalized in a lipid raft-dependent pathway, in microdomain clusters at the plasma membrane. These data suggest that WNV utilizes lipid rafts during initial stages of internalization and that the lipid rafts may contain a factor(s) that may enhance WNV endocytosis.

Infect Immun. 2008 Apr; 76(4): 1617-27
Tamayo R, Schild S, Pratt JT, Camilli A

In Vibrio Cholerae, the second messenger cyclic di-GMP (c-di-GMP) positively regulates biofilm formation and negatively regulates virulence and is proposed to play an important role in the transition from persistence in the environment to survival in the host. Herein we describe a characterization of the infection-induced gene cdpA, which encodes both GGDEF and EAL domains, which are known to mediate diguanylate cyclase and c-di-GMP phosphodiesterase (PDE) activities, respectively. CdpA is shown to possess PDE activity, and this activity is regulated by its inactive degenerate GGDEF domain. CdpA inhibits biofilm formation but has no effect on colonization of the infant mouse small intestine. Consistent with these observations, cdpA is expressed during in vitro growth in a biofilm but is not expressed in vivo until the late stage of infection, after colonization has occurred. To test for a role of c-di-GMP in the early stages of infection, we artificially increased c-di-GMP and observed reduced colonization. This was attributed to a significant reduction in toxT transcription during infection. Cumulatively, these results support a model of the V. Cholerae Life cycle in which c-di-GMP must be down-regulated early after entering the small intestine and maintained at a low level to allow virulence gene expression, colonization, and motility at appropriate stages of infection.

Biochemistry. 2008 Jan 22; 47(3): 911-21
Schnur E, Turkov M, Kahn R, Gordon D, Gurevitz M, Anglister J

Voltage-gated sodium channels (Navs) are large transmembrane proteins that initiate action potential in electrically excitable cells. This central role in the nervous system has made them a primary target for a large number of neurotoxins. Scorpion alpha-neurotoxins bind to Navs with high affinity and slow their inactivation, causing a prolonged action potential. Despite the similarity in their mode of action and three-dimensional structure, alpha-toxins exhibit great variations in selectivity toward insect and mammalian Navs, suggesting differences in the binding surfaces of the toxins and the channels. The scorpion alpha-toxin binding site, termed neurotoxin receptor site 3, has been shown to involve the extracellular S3-S4 loop in domain 4 of the alpha-subunit of voltage-gated sodium channels (D4/S3-S4). In this study, the binding site for peptides corresponding to the D4/S3-S4 loop of the para insect Nav was mapped on the highly insecticidal alpha-neurotoxin, LqhalphaIT, from the scorpion Leiurus quinquestriatus hebraeus, by following changes in the toxin amide 1H and 15N chemical shifts upon binding. This analysis suggests that the five-residue turn (residues LqK8-LqC12) of LqhalphaIT and those residues in its vicinity interact with the D4/S3-S4 loop of Nav. Residues LqR18, LqW38, and LqA39 could also form a patch contributing to the interaction with D4/S3-S4. Moreover, a new bioactive residue, LqV13, was identified as being important for Nav binding and specifically for the interaction with the D4/S3-S4 loop. The contribution of LqV13 to NaV binding was further verified by mutagenesis. Future studies involving other extracellular regions of Navs are required for further characterization of the structure of the LqhalphaIT-Navs binding site.

Microbiology. 2007 Sep; 153(Pt 9): 2964-75
Liang W, Pascual-Montano A, Silva AJ, Benitez JA

Vibrio Cholerae is the causative agent of Cholera, which continues to be a major public health concern in Asia, Africa and Latin America. The bacterium can persist outside the human host and alternates between planktonic and biofilm community Lifestyles. Transition between the different Lifestyles is mediated by multiple signal transduction pathways including quorum sensing. Expression of the Zn-metalloprotease haemagglutinin (HA)/protease is subject to a dual regulation which involves the quorum-sensing regulator HapR and the cAMP receptor protein. In a previous study, we observed that a mutant defective in the cAMP-receptor protein (CRP) expressed lower levels of HapR. To further investigate the role of CRP in modulating HapR and other signal transduction pathways, we performed global gene expression profiling of a Deltacrp mutant of El Tor biotype V. Cholerae. Here we show that CRP is required for the biosynthesis of Cholera autoinducer 1 (CAI-1) and affects the expression of multiple HapR-regulated genes. As expected, the Deltacrp mutant produced more Cholera toxin and enhanced biofilm. Expression of flagellar genes, reported to be affected in DeltahapR mutants, was diminished in the Deltacrp mutant. However, an epistasis analysis indicated that cAMP-CRP affects motility by a mechanism independent of HapR. Inactivation of crp inhibited the expression of multiple genes reported to be strongly induced in vivo and to affect the ability of V. Cholerae to colonize the small intestine and cause disease. These genes included ompU, ompT and ompW encoding outer-membrane proteins, the alternative sigma factor sigma(E) required for intestinal colonization, and genes involved in anaerobic energy metabolism. Our results indicate that CRP plays a crucial role in the V. Cholerae Life cycle by affecting quorum sensing and multiple genes required for survival of V. Cholerae in the human host and the environment.

Annu Rev Biochem. 2008; 77: 1-13
Selinger Z

The mechanism of transmembrane signaling by the receptor-activated adenylyl cyclase was an enigma. It was suggested that hydrolysis of GTP is a turn-off mechanism that resets the active adenylyl cyclase to the inactive state. To test this hypothesis, we developed a specific GTPase assay and found that the catecholamine adrenergic agonists stimulated the hydrolysis of GTP. To resolve the question of how the hormone concurrently stimulates GTP hydrolysis and activates the adenylyl cyclase, we suggested the regulatory GTPase cycle. Thus, because the hormone facilitates the binding of GTP, which is subsequently hydrolyzed, the regulatory cycle results in a hormone-stimulated GTPase activity. This model also predicts that two mechanisms could account for stimulation of adenylyl cyclase activity-either by the familiar hormone stimulation of the activation reaction or by an inhibition of the turn-off reaction. Indeed, we showed that Cholera toxin enhances adenylyl cyclase activity by inhibition of GTP hydrolysis. Finally, we also showed that the hormone-activated receptor stimulates adenylyl cyclase activity by facilitating the exchange of bound GDP for free GTP. Thus, we presented, for the first time, an explicit mechanism for receptor action.

FEMS Microbiol Ecol. 2007 Apr; 60(1): 33-9
Abd H, Saeed A, Weintraub A, Nair GB, Sandström G

Vibrio Cholerae species are extracellular, waterborne, gram-negative bacteria that are overwhelmed by predators in aquatic environments. The unencapsulated serogroup V. Cholerae O1 and encapsulated V. Cholerae O139 cause epidemic and pandemic outbreaks of Cholera. It has recently been shown that the aquatic and free-living amoeba Acanthamoeba castellanii is not a predator to V. Cholerae O139; rather, V. Cholerae O139 has shown an intracellular compatibility with this host. The aim of this study was to examine the ability of V. Cholerae O1 classical and El Tor strains to grow and survive in A. castellanii. The interaction between A. castellanii and V. Cholerae O1 strains was studied by means of amoeba cell counts and viable counts of the bacteria in the absence or presence of amoebae. The viable count of intracellularly growing bacteria was estimated by utilizing gentamicin assay. Confocal microscopy and electron microscopy were used to determine the intracellular localization of V. Cholerae in A. castellanii. The results showed that V. Cholerae O1 classical and El Tor strains grew and survived intracellularly in the cytoplasm of trophozoites, and that the bacteria were also found in the cysts of A. castellanii. The interaction showed a facultative intracellular behaviour of V. Cholerae O1 classical and El Tor strains and a possible role of A. castellanii as an environmental host of V. Cholerae species.

Eukaryot Cell. 2007 Apr; 6(4): 664-73
Sen A, Chatterjee NS, Akbar MA, Nandi N, Das P

The 29-kDa surface antigen (thiol-dependent peroxidase; Eh29) of Entamoeba histolytica exhibits peroxidative and protective antioxidant activities. During tissue invasion, the trophozoites are exposed to oxidative stress and need to deal with highly toxic reactive oxygen species (ROS). In this investigation, attempts have been made to understand the role of the 29-kDa peroxidase gene in parasite survival and pathogenesis. Inhibition of eh29 gene expression by antisense RNA technology has shown approximately 55% inhibition in eh29 expression, maximum ROS accumulation, and significantly lower viability in 29-kDa downregulated trophozoites during oxidative stress. The cytopathic and cytotoxic activities were also found to decrease effectively in the 29-kDa downregulated trophozoites. Size of liver abscesses was substantially lower in hamsters inoculated with 29-kDa downregulated trophozoites compared to the normal HM1:IMSS. These findings clearly suggest that the 29-kDa protein of E. histolytica has a role in both survival of trophozoites in the presence of ROS and pathogenesis of amoebiasis.

Scand J Immunol. 2007 Jan; 65(1): 48-53
Akhiani AA, Deelder AM, Månsson JE, Nilsson LA

We have previously reported that there is an immunological cross-reactivity between Schistosoma mansoni and Cholera toxin (CT). In this study, using an immunofluorescence technique with anti-CT antibody, we provide further evidence for this cross-reactivity by demonstrating an antigen, localized in the tegument of S. mansoni adult worms which is cross-reactive with a CT antigen. Anti-CT antibodies also reacted with structures in S. mansoni cercariae and eggs. Additionally, CT itself was found to bind strongly to the gut of the adult worm, gut cells of cercaria and the egg shell. The binding of CT to the parasite was blocked when parasite sections were incubated with CT which had been incubated with the ganglioside GM1. Lipid extraction and isolation of gangliosides demonstrated the presence of GM1 in adult worms. For further analysis of CT-binding structures, the possible interaction of CT with two major schistosome gut antigens, circulating cathodic antigen (CCA) and circulating anodic antigen (CAA), was studied. We found that CT blocked the binding of anti-CCA antibody to the gut of adult worms and that anti-CCA blocked the binding of CT to the worm gut. These findings indicate that CT binds to CCA present in the gut of the parasite and thus has, in addition to GM1, a second binding specificity.

PLoS Pathog. 2006 Oct; 2(10): e109
Nielsen AT, Dolganov NA, Otto G, Miller MC, Wu CY, Schoolnik GK

Vibrio Cholerae causes a severe diarrhoeal disease by secreting a toxin during colonization of the epithelium in the small intestine. Whereas the initial steps of the infectious process have been intensively studied, the last phases have received little attention. Confocal microscopy of V. Cholerae O1-infected rabbit ileal loops captured a distinctive stage in the infectious process: 12 h post-inoculation, bacteria detach from the epithelial surface and move into the fluid-filled lumen. Designated the "mucosal escape response," this phenomenon requires RpoS, the stationary phase alternative sigma factor. Quantitative in vivo localization assays corroborated the rpoS phenotype and showed that it also requires HapR. Expression profiling of bacteria isolated from ileal loop fluid and mucus demonstrated a significant RpoS-dependent upregulation of many chemotaxis and motility genes coincident with the emigration of bacteria from the epithelial surface. In stationary phase cultures, RpoS was also required for upregulation of chemotaxis and motility genes, for production of flagella, and for movement of bacteria across low nutrient swarm plates. The hapR mutant produced near-normal numbers of flagellated cells, but was significantly less motile than the wild-type parent. During in vitro growth under virulence-inducing conditions, the rpoS mutant produced 10- to 100-fold more Cholera toxin than the wild-type parent. Although the rpoS mutant caused only a small over-expression of the genes encoding Cholera toxin in the ileal loop, it resulted in a 30% increase in fluid accumulation compared to the wild-type. Together, these results show that the mucosal escape response is orchestrated by an RpoS-dependent genetic program that activates chemotaxis and motility functions. This may furthermore coincide with reduced virulence gene expression, thus preparing the organism for the next stage in its Life cycle.

Infect Immun. 2005 Nov; 73(11): 7375-80
Arakawa T, Komesu A, Otsuki H, Sattabongkot J, Udomsangpetch R, Matsumoto Y, Tsuji N, Wu Y, Torii M, Tsuboi T

Malaria transmission-blocking vaccines based on antigens expressed in sexual stages of the parasites are considered one promising strategy for malaria control. To investigate the feasibility of developing noninvasive mucosal transmission-blocking vaccines against Plasmodium falciparum, intranasal immunization experiments with Pichia pastoris-expressed recombinant Pfs25 proteins were conducted. Mice intranasally immunized with the Pfs25 proteins in the presence of a potent mucosal adjuvant Cholera toxin induced robust systemic as well as mucosal antibodies. All mouse immunoglobulin G (IgG) subclasses except IgG3 were found in serum at comparable levels, suggesting that the immunization induced mixed Th1 and Th2 responses. Consistent with the expression patterns of the Pfs25 proteins in the parasites, the induced immune sera specifically recognized ookinetes but not gametocytes. In addition, the immune sera recognized Pfs25 proteins with the native conformation but not the denatured forms, indicating that mucosal immunization induced biologically active antibodies capable of recognizing conformational epitopes of native Pfs25 proteins. Feeding Anopheles dirus mosquitoes with a mixture of the mouse immune sera and gametocytemic blood derived from patients infected with P. falciparum resulted in complete interference with oocyst development in mosquito midguts. The observed transmission-blocking activities were strongly correlated with specific serum antibody titers. Our results demonstrated for the first time that a P. falciparum transmission-blocking vaccine candidate is effective against field-isolated parasites and may justify the investigation of noninvasive mucosal vaccination regimens for control of malaria, a prototypical mucosa-unrelated mosquito-borne parasitic disease.

Curr Pharm Des. 2005; 11(22): 2909-26
Alfano M, Rizzi C, Corti D, Adduce L, Poli G

Natural toxins are the product of a long-term evolution, and have captured crucial events in the most essential and vital processes of living organisms. They can attack components of the protein synthesis machinery (as in the case of Diphteria and Shiga toxins, and Ribosome inactivating proteins), actin polymerization (Clostridium botulinum type C, C2, toxins and Enterotoxin A), signal transduction pathways (Cholera toxin, Heat-labile enterotoxins, Pertussis and Adenylate cyclase toxins), intracellular trafficking of vesicules (for Tetanus and Botulinum neurotoxin type C) as well as immune and/or inflammatory responses (Pyrogenic exotoxins, Cholera and Pertussis toxins). Of interest is the fact that several bacterial and vegetal toxins can either kill selectively cells infected with the human immunodeficiency virus (HIV) or exert inhibitory effects on its Life cycle. In particular both pertussis toxin (PTX) and its nontoxic B-oligomeric component (PTX-B) can block the infectious process in vitro at multiple levels, by preventing the entry of CCR5-dependent (R5) HIV strains and by inhibiting both R5 and CXCR4-dependent HIVs at post-entry level(s). In addition, some toxins possess immunostimulating properties that have been exploited in terms of adjuvancy and induction of specific cytotoxic T lymphocytes responses to different vaccine preparations, including some experimental vaccine against HIV infection. Thus, toxins may represent a relatively unexplored exhibition of powerful biological agents that could either prevent infection or attack HIV-infected cells.

Mol Microbiol. 2005 Jul; 57(2): 347-56
McLeod SM, Kimsey HH, Davis BM, Waldor MK

The genes encoding Cholera toxin, one of the principal virulence factors of the diarrhoeal pathogen Vibrio Cholerae, are part of the genome of CTXphi, a filamentous bacteriophage. Thus, CTXphi has played a critical role in the evolution of the pathogenicity of V. Cholerae. Unlike the well-studied F pilus-specific filamentous coliphages, CTXphi integrates site-specifically into its host chromosome and forms stable lysogens. Here we focus on the CTXphi Life cycle and, in particular, on recent studies of the mechanism of CTXphi integration and the factors that govern lysogeny. These and other processes illustrate the remarkable dependence of CTXphi on host-encoded factors.

DNA Cell Biol. 2004 Nov; 23(11): 723-41
Faruque SM, Nair GB, Mekalanos JJ

Vibrio Cholerae, a Gram-negative bacterium belonging to the gamma-subdivision of the family Proteobacteriaceae is the etiologic agent of Cholera, a devastating diarrheal disease which occurs frequently as epidemics. Any bacterial species encountering a broad spectrum of environments during the course of its Life cycle is likely to develop complex regulatory systems and stress adaptation mechanisms to best survive in each environment encountered. Toxigenic V. Cholerae, which has evolved from environmental nonpathogenic V. Cholerae by acquisition of virulence genes, represents a paradigm for this process in that this organism naturally exists in an aquatic environment but infects human beings and cause Cholera. The V. Cholerae genome, which is comprised of two independent circular mega-replicons, carries the genetic determinants for the bacterium to survive both in an aquatic environment as well as in the human intestinal environment. Pathogenesis of V. Cholerae involves coordinated expression of different sets of virulence associated genes, and the synergistic action of their gene products. Although the acquisition of major virulence genes and association between V. Cholerae and its human host appears to be recent, and reflects a simple pathogenic strategy, the establishment of a productive infection involves the expression of many more genes that are crucial for survival and adaptation of the bacterium in the host, as well as for its onward transmission and epidemic spread. While a few of the virulence gene clusters involved directly with Cholera pathogenesis have been characterized, the potential exists for identification of yet new genes which may influence the stress adaptation, pathogenesis, and epidemiological characteristics of V. Cholerae. Coevolution of bacteria and mobile genetic elements (plasmids, transposons, pathogenicity islands, and phages) can determine environmental survival and pathogenic interactions between bacteria and their hosts. Besides horizontal gene transfer mediated by genetic elements and phages, the evolution of pathogenic V. Cholerae involves a combination of selection mechanisms both in the host and in the environment. The occurrence of periodic epidemics of Cholera in endemic areas appear to enhance this process.

J Virol. 2004 Nov; 78(21): 12047-53
Matto M, Rice CM, Aroeti B, Glenn JS

A subpopulation of hepatitis C virus (HCV) core protein in cells harboring full-length HCV replicons is biochemically associated with detergent-resistant membranes (DRMs) in a manner similar to that of markers of classical lipid rafts. Core protein does not, however, colocalize in immunofluorescence studies with classical plasma membrane raft markers, such as caveolin-1 and the B subunit of Cholera toxin, suggesting that core protein is bound to cytoplasmic raft microdomains distinct from caveolin-based rafts. Furthermore, while both the structural core protein and the nonstructural protein NS5A associate with membranes, they do not colocalize in the DRMs. Finally, the ability of core protein to localize to the DRMs did not require other elements of the HCV polyprotein. These results may have broad implications for the HCV Life cycle and suggest that the HCV core may be a valuable probe for host cell biology.

Infect Immun. 2004 Feb; 72(2): 1019-28
Berry LJ, Hickey DK, Skelding KA, Bao S, Rendina AM, Hansbro PM, Gockel CM, Beagley KW

Chlamydia trachomatis is a pathogen of the genital tract and ocular epithelium. Infection is established by the binding of the metabolically inert elementary body (EB) to epithelial cells. These are taken up by endocytosis into a membrane-bound vesicle termed an inclusion. The inclusion avoids fusion with host lysosomes, and the EBs differentiate into the metabolically active reticulate body (RB), which replicates by binary fission within the protected environment of the inclusion. During the extracellular EB stage of the C. trachomatis Life cycle, antibody present in genital tract or ocular secretions can inhibit infection both in vivo and in tissue culture. The RB, residing within the intracellular inclusion, is not accessible to antibody, and resolution of infection at this stage requires a cell-mediated immune response mediated by gamma interferon-secreting Th1 cells. Thus, an ideal vaccine to protect against C. trachomatis genital tract infection should induce both antibody (immunoglobulin A [IgA] and IgG) responses in mucosal secretions to prevent infection by chlamydial EB and a strong Th1 response to limit ascending infection to the uterus and fallopian tubes. In the present study we show that transcutaneous immunization with major outer membrane protein (MOMP) in combination with both Cholera toxin and CpG oligodeoxynucleotides elicits MOMP-specific IgG and IgA in vaginal and uterine lavage fluid, MOMP-specific IgG in serum, and gamma interferon-secreting T cells in reproductive tract-draining caudal and lumbar lymph nodes. This immunization protocol resulted in enhanced clearance of C. muridarum (C. trachomatis, mouse pneumonitis strain) following intravaginal challenge of BALB/c mice.

Vaccine. 2003 Jul 4; 21(23): 3143-8
Arakawa T, Tsuboi T, Kishimoto A, Sattabongkot J, Suwanabun N, Rungruang T, Matsumoto Y, Tsuji N, Hisaeda H, Stowers A, Shimabukuro I, Sato Y, Torii M

Transmission-blocking vaccines (TBVs) targeting ookinete surface proteins expressed on sexual-stage malaria parasites are considered one promising strategy for malaria control. To evaluate the prospect of developing non-invasive and easy-to-administer mucosal malaria transmission-blocking vaccines, mice were immunized intranasally with a Plasmodium vivax ookinete surface protein, Pvs25 with a mucosal adjuvant Cholera toxin (CT). Immunization induced significant serum IgG with high IgG1/IgG2a ratio (indicative of Th-2 type immune response). Feeding Anopheles dirus mosquitoes with mixtures of immune sera and gametocytemic blood derived from vivax-infected volunteer patients in Thailand significantly reduced both the number of midgut oocysts as well as the percentage of infected mosquitoes. The observed transmission-blocking effect was dependent on immune sera dilution. This study demonstrates for the first time that the mucosally induced mouse immune sera against a human malaria ookinete surface protein can completely block parasite transmission to vector mosquitoes, suggesting the possibility of non-invasive mucosal vaccines against mucosa-unrelated important pathogens like malaria.

Semin Pediatr Infect Dis. 2002 Oct; 13(4): 289-99
Ligon BL

Tuberculosis has been a major cause of death for centuries. Likewise, anthrax has posed a deadly threat to both farm animals and humans and today poses a threat as a weapon of biological warfare. Cholera, which wreaked havoc in the East and threatened to enter Europe, also posed a deadly threat. The causes of these diseases remained mysteries for centuries. Nobel laureate Robert Koch (1843-1910), often called the founder of medical bacteriology, is credited with discovering the tubercle bacillus, Mycobacterium tuberculosis; with demonstrating for the first time in history the Life cycle of the anthrax bacillus under controlled in vitro conditions; and with identifying Vibrio cholorae as the cause of Cholera. In later Life, he also was at the center of several controversies. This article provides a brief summary of Koch's exploration into bacteriology and, especially, his experience with tuberculosis and the controversies that developed in the latter part of his Life, as well as his childhood and early adult years and the development of his now well-known "postulates." Copyright 2002, Elsevier Science (USA). All rights reserved.

Curr Issues Intest Microbiol. 2002 Sep; 3(2): 29-38
Peterson KM

Vibrio Cholerae, the causative agent of Asiatic Cholera, is a gram-negative motile bacterial species acquired via oral ingestion of contaminated food or water sources. The O1 serogroup of V. Cholerae is responsible for pandemic Cholera and is divided into two biotypes, classical and El Tor (Butterton and Calderwood, 1995; Mekalanos, 1985). The El Tor biotype is responsible for the current Cholera pandemic. In the absence of disease, the vibrio Life cycle consists of a free-swimming phase in marine and estuarine environments in association with zooplankton, crustaceans, insects, and water plants. Vibrios interact with various surfaces found in the environment to generate biofilms which may promote survival (Watnick etaL, 1999). Within the host the motile vibrios must evade the innate host defense mechanisms, penetrate the mucus layer covering the intestinal villi, adhere to and colonize the epithelial surface of the small intestine, assume a non-motile phase, replicate and cause disease by secreting numerous exoproteins at the site of infection (Oliver and Kaper, 1997). The voluminous diarrhea associated with Cholera infection leads to the dissemination of the vibrios back into a watery environment and thus a continuation of the environmental phase of the Life cycle. The host phase of the vibrio Life cycle is only possible through the action of a group of virulence genes (ToxR-regulon) controlled by a complex and incompletely understood regulatory cascade. The ToxR regulon colonization and toxin genes are coordinately expressed in response to specific host signals that have yet to be completely defined (Skorupsky and Taylor 1997). Although little is known regarding the host signals that impact the ToxR regulatory cascade, it is clear that these intraintestinal signals play an important role in maximizing the ability of the vibrios to survive and multiply within the host. Key to understanding the complex events involved in the pathogenesis of V. Cholerae will be elucidating the intraintestinal signaling molecules that trigger the expression of vibrio virulence genes. Understanding the molecular basis of this host-parasite interaction will provide important information with respect to how pathogenic bacteria establish infection and provide insights leading to novel methods for treating and/or preventing bacterial infections. This review will summarize what is known regarding host signaling and the complex ToxR regulatory system employed by V. Cholerae to coordinate virulence gene expression within the host.

Arch Med Res. 2002 Jul-Aug; 33(4): 371-8
Sciutto E, Fragoso G, Manoutcharian K, Gevorkian G, Rosas-Salgado G, Hernández-Gonzalez M, Herrera-Estrella L, Cabrera-Ponce J, López-Casillas F, González-Bonilla C, Santiago-Machuca A, Ruíz-Pérez F, Sánchez J, Goldbaum F, Aluja A, Larralde C

Cysticercosis caused by Taenia solium frequently affects human health and rustic porciculture. Cysticerci may localize in the central nervous system of humans causing neurocysticercosis, a major health problem in undeveloped countries. Prevalence and intensity of this disease in pigs and humans are related to social factors (poor personal hygiene, low sanitary conditions, rustic rearing of pigs, open fecalism) and possibly to biological factors such as immunity, genetic background, and gender. The indispensable role of pigs as an obligatory intermediate host in the Life cycle offers the possibility of interfering with transmission through vaccination of pigs. An effective vaccine based on three synthetic peptides against pig cysticercosis has been successfully developed and proved effective in experimental and field conditions. The well-defined peptides that constitute the cysticercosis vaccine offer the possibility to explore alternative forms of antigen production and delivery systems that may improve the cost/benefit of this and other vaccines. Encouraging results were obtained in attempts to produce large amounts of these peptides and increased its immunogenicity by expression in recombinant filamentous phage (M13), in transgenic plants (carrots and papaya), and associated to bacterial immunogenic carrier proteins.