Vibrio cholerae-A Review

Vibrio cholerae is a facultative anaerobic, Gram negative, non-spore forming curved rod, about 1.04-1.06 μm long. It is a facultative human pathogen found in coastal waters that causes the acute gastrointestinal disease, cholera, a major health threat in poor nations. It is widely acknowledged as one of the most important water borne pathogen of worldwide economic significance. Sea foods and water is the most common vehicle for this infection in humans. It has been isolated from wide variety of samples such as seawater, sediments, plankton, finfish and shellfishes of coastal and estuarine environments. Cholera pathogenesis is a complex process and involves synergistic action of several genes. CT is considered the most important epidemic marker among various toxins produced by V.cholerae. Detection of V.cholerae from food stuffs is problematic, since they are present at low level together with large number of competing microflora and also they may be injured by different food processing methods.


Introduction
has a specific function.The B subunit serves to bind the holotoxin to the eukaryotic cell receptor, and the A Cholera, an enteric diarrheal disease caused by subunit possesses a specific enzymatic function that the gram-negative bacterium Vibrio cholerae, acts intracellular.Recent studies of the aquatic continues to be a worldwide health concern.Two environment have shown that V. cholerae, including distinctive epidemiologic features of cholera are its strains of O1and O139, are normal inhabitants of tendency to appear in explosive outbreaks, often surface water, particularly brackish waters, and starting in several distinct foci simultaneously, and its survive and multiply in association with zooplankton propensity to cause true pandemic that progressively and phytoplankton quite independently of infected affect many countries in multiple continents over the human beings (Huq et al., 1983).course of many years (Kaper et al., 1995).V. cholerae, Etiological studies on acute diarrhoeal diseases the causative agent of cholera in humans, is classified in gangetic plain areas have shown that gastroenteritis into two serotypes: O1 and non O1 (Chatterjee and caused by V. cholerae ranks first in terms of incidence Maiti, 1984).The O1 serogroup of V. cholerae is followed by V. parahaemolyticus in India (Sakazaki et further classified into two biotypes, namely, the al., 1971) and other developing countries (Albert et classical and El Tor biotypes.In 1993, V. cholerae al., 1993).Cholera has been categorized as one of the serogroup O139 made an explosive appearance and emerging and re-emerging infections in developing caused a severe epidemic in the Indian continent countries (Satcher, 1995) and is classified as Category (Ramamurthy et al., 1993).The major surface antigen B bioterrorism by Centre for Disease Control and employed in characterization of V. cholerae is the O Prevention (WHO, 2008).antigen.According to the typing scheme of Sakazaki and Shimada, there are 139 different O groups.V.
The Centre for Disease Control and Prevention cholerae (CDC) estimated that 76 million food borne illnesses O1 and O139 are known to be the dominating and pathogenic strains.
occurred in the United States with 325,000 However, the pathogenicity of Vibrio cholerae is hospitalizations and 5,200 deaths (Mead et al., 1999).chiefly associated with the secretion of the Cholera History and Epidemiology of the cholera toxin (CTX), which is a protein complex.CTX is responsible for the harmful effects of cholera Cholera is one of the oldest and best understood infection.The structure of CTX is typical of the A-B of the epidemic-prone disease.The ancestral home of subunit group of toxins in which each of the subunits cholera is thought to be the Ganges delta on the Indian Pathogenicity for humans and Virulence subcontinent, where epidemic of cholera like disease were described as far back as the 16th century factors (Kindhauser, 2003).John Snows observations on Infection due to Vibrio cholerae begins with the cholera during 1848 London epidemic helped to ingestion of contaminated water or food.After passage establish concept of a living agent, as cause of disease through the acid barrier of the stomach, the organism and supported the theory of waterborne transmission colonizes the epithelium of the small intestine by of cholera (Winkelstein, 1995).In 1883, during the means of the toxin-co regulated pili (Taylor et al., fifth pandemic Robert Koch, successfully isolated the 1987) and possibly other colonization factors such as agent of cholera and suggested the existence of CT in the different haemagglutinins, accessory colonization 1884 (Finkelstein, 2000).In 1953, SN De (De and factor and core encoded pilus, all of which are thought Chatterjee, 1953), bacteriologist in Calcutta discovered to play a role.Cholera enterotoxin produced by the the crude cholera toxin, responsible for stimulating adherent vibrios is secreted across the bacterial outer fluid secretion from the small intestine.
membrane into the extracellular environment and There have been seven pandemic of cholera in disrupts ion transport by intestinal epithelial cells.The recorded history.The classical V. cholerae O1was subsequent loss of water and electrolytes leads to the responsible for the fifth and sixth pandemic and is severe diarrhea characteristic of cholera.believed to have been associated with the earlier The major virulence-associated factors are pandemic as well, although there is no hard evidence present in cluster (Hacker et al., 1997) with at least (Baruda, 1992).The causative agent of the seventh three regions in V.cholerae chromosome.The first is pandemic is the E1Tor biotype (Samadi et al., 1983).the CTX genetic element (Mekalanos, 1985) which In December, 1992, a large epidemic of cholera began has been reported to compromise the genome of a in Bangladesh.The new serogroup has been filamentous bacteriophage (CTX ? ) (Waldor and categorized as V. cholerae O139, with synonym Mekalanos, 1996).The second region is a large Bengal to refer to it first isolation from areas pathogenicity island for V.cholerae (VPI) (Karaolis et surrounding the Bay of Bengal (Shimada et al., 1993) al., 1998) that encode a toxin regulated pilus (TCP) possibly working the beginning of the eighth gene cluster, a type IV pilus that function as an pandemic (Swerdlow and Ries, 1993).essential colonization factor (Taylor et al., 1987) and Cholera has re-emerged as a major infectious act as CTX ?receptor (Waldor and Mekalanos, 1996).disease in recent past, with a global increase in its The third gene cluster, the RTX gene cluster in V. incidence.In 1994, cholera cases were notified from cholerae encodes the presumptive cytotoxin (rtxA), an 94 countries-the highest ever number of countries in acyltransferase (rtxC), and an associated ATP-binding one year (WHO, 1995).Cholera is one of the three cassette transporter system (rtxB and rtxD, two proteins for toxin transportation) (Lin et al., 1999).diseases requiring notification to WHO under the International Health Regulation.It is endemic V. cholerae virulence cassette or CTX element corresponds to genome of CTX ?, a lysogenic throughout much of the African continent, where it thrives under conditions of poor sanitation and waste filamentous bacteriophage has given a way for disposal.In 2006, the total number of cases reported in emergence of new clones of toxigenic V. cholerae strains (Waldor and Mekalanos, 1996).Africa accounted for 99% of the global total.Africa CT is clearly the most important causative factor has been the continent with the highest number of officially reported cholera cases since 1996 in the disease cholera, CT deficient isolates of V. (Kindhauser, 2003).Cholera remains a global threat to cholerae also elicit mild to severe diarrhea and other reactogenic symptoms in human indicating that other public health, especially in developing countries toxins are likely to contribute to pathogenesis of the (WHO, 2008).
disease (Coster et al., 1995) cyclase activation in small intestinal epithelial cells, associated with extraintestinal infection with leading to the loss of fluid and electrolytes.The 5 septicemia, wound infection, ear infection, cellulitis, binding (B) subunits of 11500 Da each serves to bind peritonitis, necrotizing fascitis, cholecystitis, the toxin to the epithelial cell surface receptor, GM1.endophthalmitis and meningitis (Yang et al., 2008).The genes expressing A and B subunits are designated These symptoms are seen in patients with diabetes ctxA and ctxB, respectively, and are expressed as a mellitus, chronic renal failure and dialysis, single transcriptional unit (Mekalanos et al., 1983).immunocompromized patient and post splenectomy.Toxin production does not correlate with serotype Water borne infection (Kaper et al., 1981).The effect is dependent on a specific receptor, monosialosyl ganglioside (GM1 Cholera is usually transmitted by ingestion of contaminated water and sewage contaminated water ganglioside) present on the surface intestinal mucosal remains the primary vehicle for cholera outbreaks cells (Guidolin and Manning, 1987).
Although not fully characterized, other toxins (Tauxe and Blake 1992).Sewage contamination of produced by V.cholerae include the shiga-like toxin ground water in Delhi was responsible for the ( during intense phytoplankton blooms has supported Infection due to V.cholerae begins with the growth of V. cholerae in seawater.The toxigenic V. ingestion of food or water contaminated directly or cholerae is a native flora of the aquatic environment indirectly with faeces or vomitus of infected person which is transmitted through drinking water and still (CDC, 2003).
remains the leading cause of morbidity and mortality Infection of approximately 104-106 V.cholerae in many developing countries including Thailand O1 organisms is likely to produce clinical (Chomvarin et al., 2007).cholera (Cash et al., 1974).A dose of V.cholerae O1 Food borne infection (106 cells) was normally needed to cause diarrhea (Levine et al., 1981).
a. Fruits and vegetables: In many countries, the The incubation period for cholera ranges from a practice of fertilizing gardens with untreated night soil few hours to five days, usually two to three days and the habit of consuming uncooked vegetables have followed by acute watery diarrhoea, often associated often resulted in cholera outbreaks.Vegetables may be with vomiting, muscle cramps and complications contaminated during washing with polluted water.related to severe dehydration.The water diarrhoea is This can also occur when contaminated water is speckled with flakes of mucus and epithelial cells injected into fruits, such as watermelons, to preserve (rice-water stool).Cardiac complications and their weight and taste (Feachem, 1981).The pH of a circulatory failure occur due to loss of potassium.In specific fruit is an important factor that influences severe cases, fluid loss of 500-1000 ml, an hour can contamination by V. cholerae.Sour fruits such as occur, which may result in death in less than 24 hrs lemons and oranges, with lower pH (below 4.5) do not V. cholerae et al.
concentrate preserved in cans are also less likely to be Cholera enterotoxin is major virulence factor responsible for profuse diarrhoea, typically known as contaminated if they have an acidic pH.Spices, cholera gravis, characterized by profuse watery including raw onions and garlic, can support the diarrhoea, vomiting and dehydration, often associated survival of V. cholerae for 2-3 days at ambient temperature (Felsenfeld, 1967).with leg cramps due to electrolyte imbalance leading b.Seafoods: The importance of fish and shellfish as a to severe dehydration and death (Choopun et al., 2002).
vehicle of cholera has been recognized by early V. cholerae is non invasive enterotoxigenic observers.Fishes are likely to be contaminated by V. organism causing gastroenteritis, whereas non O1 is cholerae when the surrounding water is contaminated weeks during storage under refrigeration (Depaola, by the sewage or other environmental sources of V. 1981).Huq et al. (1983) reported that oysters get the cholerae O1.It has been shown that V. cholerae can infection of V. cholerae due to feeding on plankton to survive in seawater in association with zooplankton which V. cholerae organisms are attached due to (copepods).Zooplankton secretes a self-protective production of chitinase.Consumption of raw oysters coat of chitin that can be dissolved by chitinase, an correlated strongly with gastrointestinal infections in enzyme produced by V. cholerae O1.Seafoods, which V. cholerae has been implicated as causative including mollusks, crustaceans, crabs, and oysters, agent (Rippey, 1994).It has been reported that V. feed on plankton and can become infected with V. cholerae exist in water with a salinity of 3-8% only cholerae.Once infected, particularly clams, and (Sousa et al., 2004).oysters can harbour V. cholerae for weeks, even if g. Dairy Products: V. cholerae O1 can survive for more than two weeks in different dairy products, refrigerated (Depaola, 1981).In crabs, the organisms including milk, milk products, soft deserts, and cakes.can rapidly multiply at ambient temperature, and boiling for less than 10 minutes or steaming for less Addition of sugar and eggs enhances bacterial than 30 minutes does not completely kill V. cholerae survival.Although V. cholerae is killed by (Huq et al., 1983).
pasteurization of milk, the organisms can persist in c.Fish: Raw fish consumption was the cause for raw milk as long as four weeks, even if refrigerated cholera outbreaks in Japan as early as 1886 (Felsenfeld, 1967).(Donitz, 1892) and in Philippines in 1908 (Heiser, h.Poultry and meat: Contamination of meat of 1908).V. cholerae was isolated from salted fish animal origin occurs exogenously during processing, responsible for cholera outbreaks in Guan during 1974 cooking, storage or consumption.It has been shown (Kuberski et al., 1979).Feldhusen (2000) reported that that V. cholerae can live and grow on cooked chicken, raw fish was initially implicated epidemiologically as an increase in numbers of V. cholerae from 103 to 106 a source of transmission of V. cholerae in the South within 16 hours has been demonstrated (Kolvin and American epidemic in 1991.V.cholerae O1 was Roberts, 1982).An early observation by Seligmann present in 0.2% of raw fishery products, whereas V. indicates that consumption of improperly cooked cholerae non O1 was present in 26.3% of raw and horsemeat was incriminated in a small outbreak of 12.14% of frozen products in Kerala and Tamil Nadu cholera in Berlin in 1918 (Seligman, 1918).The meat coasts during 1986-87 (Verma et al., 1989).Fish had been prepared by an infected butcher who samples from fresh as well as marine waters carry succumbed to cholera the next day.There are many V.cholerae and it has been reported that fish intestine other types of food that may be contaminated with V. contained 5 X 103 V. cholerae cfu/g (Senderovich et cholerae.V. cholerae can survive on cooked rice, al., 2010) potato, eggs, and pasta for up to 5 days, and can also d.Shellfish: Ingestion of aquatic vegetation or survive in spices, including pepper and cinnamon, for sewage contamination of water are the main up to several days (PAHO, 1991).contamination sources of V. cholerae in shellfish Diagnosis (Colwell, 1990).Garate Lizarranga et al. (2006) reported that V. cholerae adhere strongly to shellfishs The conventional isolation procedure includes growth in enrichment broth like Alkaline Peptone digestive tract and cannot be removed efficiently by o rinsing the shellfish or depuration.Gholami et al. water or Luria broth (LB) at 37 C for 18-24 hr to increase (1998) studied the risk factor of V. cholerae among the ratio of V. cholerae to competitor organisms and renal diseased patients and reported that the infections plating on selective medium, TCBS i.e.Thiosulfatewere usually acquired by raw shellfish which has Citrate-Bile salts-Sucrose agar (Finkelstein, 1988) for o damaged the kidney.
24-48 hr at 37 C. V. cholerae ferment sucrose and e. Crabs: Inadequately steamed crabs infected with V. produce yellow colonies.So, this medium is widely cholerae were responsible for outbreaks of cholera in used for isolation of V. cholerae.These colonies are Louisiana, USA (Blake et al., 1980).In crabs, the submitted to the oxidase test for the identification of V. organisms can rapidly multiply at ambient cholerae complemented by biochemical and serological temperature and boiling for less than 10 minutes or tests (Sack et al., 1980).steaming for less than 30 minutes does not completely  85-102.In, Oven, P. and Foster, T.J.(ed.),Immunochemical and molecular genetic analysis of bacterial pathogens.