The toxin attaches to a specific receptor ganglioside Gl on the cell membrane of intestinal cells and activates the enzyme adenylate cyclase. The rise in the internal concentration of cAMP causes an efflux of water, sodium, potassium, chloride and carbonate ions from the cells of the mucous membrane, and this is the main cause of diarrhea [ 7 ]. Cholera has been a well known disease since the 19th century. In the 19th and 20th centuries, seven major pandemics are recognized. The first six pandemics occurred during the following periods: 1st: —, 2nd: —, 3rd: —, 4th: —, 5th: —, 6th: — These pandemics all started in Asia, passed through Europe and then reached South America.
The Classical biotype was involved. The seventh pandemic, still in course, started in in the Celebes Isles, in Asia. In the s, the disease spread through Asia, in the s reached the Middle East and Africa, and in streaked violently across South America.
Water Microbiology. Bacterial Pathogens and Water
Now El Tor has replaced the Classical biotype. El Tor biotype had been detected before, in , but only in the development of the seventh pandemic did this biotype replace the Classical one and become dominant [ 1 , 7 , 8 , 10 , 11 ]. In , a new serovariety O , which was coined the Bengal serovariety, was detected for the first time in Bangladesh. This new serovariety quickly spread to India and to southeastern Asia, displacing O1.
Although serovariety O1 El Tor has reappeared in and , the Bengal serovariety still remains the dominant one. The illness caused by serovarieties O and O1 are indistinguishable [ 8 , 12 , 13 ]. In , the seventh pandemic entered South America through the coastal area of Peru. On 23 January, in Chancay, north Peru, Vibrio cholerae O1 El Tor was isolated from patients with cholera symptoms, confirming the disease.
In this region, between 24 January and 9 February, 1, people were hospitalized and 66 died.
Rapid microbiological methods
From Peru, the disease spread rapidly to other countries in South America. Shellfish and fish nourishing on this zooplankton became contaminated and the bacterium was transmitted to humans who ate these marine foods [ 14 — 17 ]. The misfortune of people who died in the first months of this disastrous South American cholera epidemic appeared to have unleashed scientists to study the disease harder and, indeed, important epidemiological studies were carried out during this outbreak.
These studies confirmed that contaminated uncooked food and beverages can also be a vehicle for transmission of cholera [ 18 ]. In addition to the gene encoding cholera toxin production, this segment virulence cassette include an accessory cholera toxin ace , a zonula occludens toxin zot , core encoded pilin cep , and an open reading frame of unknown function.
This process was demonstrated in vitro in cell suspensions and in vivo in the gut of the rat [ 8 , 13 , 19 , 20 ]. Epidemic and pandemic strains of V. VPI is The tcp gene encodes for the This VPI segment appears to be transferable from V. They have been isolated from many estuarine animals such as birds, frogs, fishes and shellfish, and survive and multiply on the surface of phytoplankton and zooplankton cells [ 8 , 21 ]. They survive in the cultivable state in water and aquatic and marine organisms for a considerable period of time [ 8 , 12 , 22 — 24 ].
When V. Cells display a certain metabolism, but are not able to growth and multiply on the surface of agarized media and give rise to colonies.
Microbiological assessment of sachet water “pure water” from five regions in Ghana
Cells in this viable but non-culturable state retain viability as well as the potential for pathogenicity for significant periods of time [ 25 — 27 ]. Viable but non-culturable cells can leave their dormant stage and multiply again, resulting in an explosion of their concentration in the environment. Since the presence of non-toxigenic strains is common in aquatic milieu, especially in estuaries, if a horizontal transfer of cholera exotoxin producing genes occurs between toxigenic and non-toxigenic strains, the number of toxigenic cells in the environment can rise rapidly and pronouncedly.
The episodic nature and the sudden appearance of violent cholera outbreaks, followed by a rapid slowing down, are probably related with these phenomena. Antigenic analysis began when Castellani described, in , a method for absorbing antisera. The first antigenic scheme for Salmonella was published by White in , and subsequently developed extensively by Kauffmann, in two classical works published in and [ 28 , 29 ].
The Kauffmann-White antigenic scheme contained, by , about 2, different serovars [ 28 , 29 ]. The genus Salmonella , a member of the family Enterobacteriaceae , include Gram-negative motile straight rods. Cells are oxidase-negative and catalase-positive, produce gas from D-glucose and utilize citrate as a sole carbon source. Salmonellae have several endotoxins: antigens O, H and Vi [ 28 , 29 ].
The taxonomy and nomenclature of the genus Salmonella has been subject of debate since Le Minor and Popoff proposed changes in a paper published in The issue was settled by a decision of the International Committee on the Systematics of Prokaryotes and published in The current taxonomy of the genus is presented in Table 4. According to the rules of bacterial nomenclature, the names of the serovars are not italicized and the first letter must be a capital [ 28 — 30 ]. Current taxonomy and nomenclature of the genus Salmonella. Habitat and pathogenicity of main serovars a. However, locally, other serovars can be predominant.
In the period —, Tunisia was exposed to salmonellosis outbreaks in , , and In , salmonellosis outbreak was caused by serovar Mbandaka. In , three salmonellosis outbreaks were reported from hospitals located in three different regions.
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In , a S. In that year, the Livingstone serovar jumped to the first position in human infection in Tunisia. The source of isolation was a fermented juice traditionally extracted from palm-tree [ 31 ]. Salmonellae pathogenic to humans can cause two types of salmonellosis: 1 typhoid and paratyphoid fever do not confuse with typhus, a disease caused by a rickettsia ; 2 gastroenteritis [ 28 ].
Low infective doses less than 1, cells are sufficient to cause clinical symptoms.
Salmonellosis of newborns and infants presents diverse clinical symptoms, from a grave typhoid-like illness with septicemia to a mild or asymptomatic infection. In pediatric wards, the infection is usually transmitted by the hands of staff [ 29 ]. Food-borne Salmonella gastroenteritis are frequently caused by ubiquitous Salmonella serovars such as Typhimurium. About 12 h following ingestion of contaminated food, symptoms diarrhea, vomiting and fever appear and last 2—5 days. Spontaneous cure usually occurs. Salmonella may be associated with all kinds of food. Vegetables and fruits may carry Salmonella when contaminated with fertilizers of fecal origin, or when washed with polluted water [ 28 ].
maisonducalvet.com/hombres-solteros-riaza.php The incidence of typhoid fever decreases when the level of development of a country increases i. Where these hygienic conditions are missing, the probability of fecal contamination of water and food remains high and so is the incidence of typhoid fever [ 29 ].
The principal habitat of Salmonella is the intestinal tract of humans and animals [ 28 ]. Salmonellae are constantly found in environmental samples, because they are excreted by humans, pets, farm animals, and wild life.
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Municipal sewage, agriculture pollution, and storm water runoff are the main sources of these pathogens in natural waters [ 1 , 32 ]. Salmonellae do not seem to multiply significantly in the natural environment, but they can survive several weeks in water and in soil if conditions of temperature, humidity, and pH are favorable [ 28 ].
Salmonellae isolated from environmental sources are predominantly non-Typhi or Paratyphi serovars. In a study carried out in Tunisia during —, S. The great majority of the strains were isolated from poultry, red meat, milk and dairy products, vegetables and fruits. Serovars Corvallis, Enteritidis, and Anatum were the commonest [ 31 ]. Arvanitidou et al. A total of 29 Salmonella species were recovered from the water samples. Many of the isolated Salmonella serovars were of non-human animal origin such as Mbantaka, Virchow, Hadar, Infantis and Senftenberg, commonly isolated from poultry farm.
Unlike cholera, humans infected with salmonellae can carry the bacteria in the gut without signs of disease. Infected humans can harbor the bacteria for considerable periods of time. These people can be chronic holders of the bacterium in the gut, and constitute the main reservoir of the bacteria in the environment [ 29 ]. The salmonellosis cycle in the environment can involve shellfish. Salmonellae survive sewage treatments if suitable germicides are not used in sewage processing.
If effluent from the sewage plant passes into a coastal area, edible shellfish mussels, oysters can become contaminated. Shellfish concentrate bacteria as they filter several liters of water per hour. Ingestion by humans of these seafoods uncooked or superficially cooked may cause typhoid fever or other salmonellosis. Evidence of such a cycle has been obtained by the use of strain markers, including phage typing [ 29 ]. Shigella are Gram-negative, non-sporeforming, non-motile, straight rod-like members of the family Enterobacteriaceae.
Cells ferment sugars without gas production. Salicin, adonitol and myo-inositol are not fermented. Cells do not utilize citrate, malonate and acetate as sole carbon source and do not produce H 2 S. Lysine is not decarboxylated.
Cells are oxidase-negative and catalase-positive.