College of Medicine Microbiology BacteriologyVibrio cholerae: Dr.Jawad Kadhim Tarrad----------------------------------------------------------------------------------------- Important properties:

Gram-negative rod in comma-or S-shaped. Non capsulated. It is active motile by single flagellum. Facultative anaerobic.

Antigenic structure and virulence factors: Somatic antigen(O-antigen): V. cholerae has many antigenic groups

according to O-antigen. Only serogroup-O1 and O139 members were associated with severe diarrhea and epidemic cholera. Other serogroups, non-O1 and non-O139, are either non-pathogenic or cause mild diarrhea.

V.cholerae O1 has two biotypes; El-Tor and classical cholera. Each biotype divided into three serotypes: Ogawa, Inaba and Hikojima.

Flagella (H-antigen) and Mucinase allow the organism to migrate and penetrate thick mucous layer that cover intestinal epithelial cells and it migrates through mucous layer.

Cholera toxin is major virulence factor and it consists of two subunits (2A-5B). The A-subunit consist of two units (A1 and A2). The B-subunit is composed of five identical units arranged in ring around central subunit A. The A-subunit linked to B-subunit by disulfide bond.

Source and transmission: Natural habitats are human intestine. The organism is transmitted from person to person by ingestion of fecal

contaminated water and food. V.cholerae proliferates in summer months when water temperature more than

20C (warm water ), therefore most cases occur in warm months. Pathogenesis:

V. cholerae is pathogenic for human only. It colonize the small intestinal tract in very high number. For colonization to occur, large numbers of inoculating organism(107cells) must ingest when the vehicle is water because the organism is sensitive to stomach acid and rapidly killed by it. While when the vehicle is food , as few as 102-103 organisms because buffering capacity of food. Therefore, persons who taking antacid or have gastrectomy, are much more susceptible to infection.

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The organism adheres to microvilli of brush border of epithelial cells of small intestine, and multiplies. The organism secrets mucinase, which dissolve the protective layer that cover intestinal epithelial cells.

After multiplication, the organism secretes cholera toxin. Mode of toxin action:

The B-subunit binds to receptor on surface of enterocytes. The A-subunit is inserted into cytosol, where it catalyze the addition of ADP-ribose to G-protein which causes the stimulation of adenylate cyclase to convert ATP to cAMP .

The overproduction of cyclic AMP and activation of protein kinase-A resulting in stimulates the secretion of chloride ion and water, leading to massive watery diarrhea without inflammatory.

Disease and clinical findings: The organism cause cholera disease(vibriosis). It is severe gastroenteritis.

After I.P : 1-3 days, the major symptoms of cholera infection are watery diarrhea in large volumes. There is no abdominal pain, no fever, in some cases may vomiting occur. About 60% of cases develop a severe diarrhea known as rice-water stool (containing flecks of mucus). The feces contain epithelial cells, mucus, no RBCs ,no WBCs (cholera diarrhea is toxigenic, no inflammatory).

In severe cases, increase secretion(out flow) of chloride ion, bicarbonate and water, in same time the reabsorption of sodium ion and chloride is inhibited. so rapid loss of massive fluid and electrolytes as much as 1 liter of fluid may be lost each hour (20 liter or more in day) which cause dehydration and loss 12% of body weight. Acidosis and hypokalemia occur as result of loss of bicarbonate and potassium in stool. Also the loss of fluid and electrolytes lead to cardiac and renal failure.

Cholera is not invasive infection. The organism does not reach the bloodstream.

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Mortality and death are due to dehydration and electrolytes imbalance. Severe dehydration leads to hypovolemic shock, which can result in death if untreated. However, if treatment is instituted promptly, the disease runs self-limited course in up to 7 days. Mortality rate without treatment is 40-60%.

Lab. Dx: Gram-staining shows gram-negative rods in curved shape. Stool culture: culturing on TCBS and MacConkey medium. Serological tests as agglutination test is used in confirmation of cholera

serotypes. Prevention and therapy: Treatment:

Re-hydration therapy by oral or intravenous administration of solution containing glucose and electrolytes should be given immediately.

Antibiotic therapy does not affect the disease once the toxin attaches to intestinal cells but can prevent later attack by reducing the number of cholera organism in the intestine. Drug of choice for treatment of cholera is tetracycline.

Prevention: Immunization with toxoid vaccine, this vaccine provides only limited

protection for short period approximately 6 months. The patients should be isolated. The water and foods should be treated with good sterilization and good

cooking and preserving food.

Campylobacter jejuni: Important properties:

Gram-negative rods arranged in comma shape. motile by single polar flagellum. It is capsulated.

Virulence factors: Capsule. Enterotoxin. Cytotoxin. Endotoxin.

Source and transmission: Domestic animals and poultry (cattle, chicken, dogs, cats) are serve as source

of infection. Humans are become infected by ingestion of food (poultry, meat, milk)and

water contaminated with animal feces. Pathogenesis:

C.jejuni is sensitive to gastric acid, so must be ingestion about 104 cells to produce infection.

The organism multiply in small intestine(jejunum,ileum), invade epithelium, and produce inflammation that results in appearance of red and white blood cells in stool. Other site of infection may involve is colon.

The organism produces enterotoxin( that acts in same manner of cholera toxin) and cytolethal distending toxin(CDT).

Watery diarrhea is mediated by enterotoxin, while dysentery results from cellular invasion and destruction of mucosal surface, which is mediated by cytotoxin and host inflammatory response. Bactereamia may occur.

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Disease and clinical features: C.jejuni is frequent cause of enterocolitis especially in children. After I.P(2-

10days),the disease is characterized by watery or dysentery, foul-smelling diarrhea, followed by bloody stool accompanied by fever and severe abdominal pain.

C.jejuni is cause of both traveler diarrhea and pseudoappendicitis. Autoimmune diseases; gastrointestinal infection associated with Guillian-

Barre syndrome, which is autoimmune disease attributed to formation of antibodies against C.jejuni that cross-react with antigens on neuron, lead to acute neuromascular paralysis. Campylobacter is also associated with other autoimmune diseases like; reactive arthritis and Reiter syndrome.

Epidemiology: The infection is zoonotic disease and it acquired by oral route from food, drink

or contact with infected animals or animal products. This organism is common cause of diarrhea. The disease is estimated 2 million

cases occur in USA each year. Lab.Dx:

Primary isolation of C.jejuni is difficult and requires elevated temperature 42Ċ, reduced oxygen 5%, and increased carbon dioxide 10%.

It can be cultured on selective medium with antibiotic such as Skirrow medium under above condition.

Control: Erythromycin or ciprofloxacin is used successfully in enterocolitis. Fluid and electrolytes replacement in severe diarrhea. Good cooking of food and pasteurization of milk. No vaccine is available.

Helicobacter pylori: Important properties:

Gram-negative rod in Comma or S-shaped or spiral shape(helical). It is rapid motile. Strongly urease-positive.

Virulence factors:1. Urease catalysis the hydrolysis of urea and production of ammonia, creating

alkaline or neutral microenvironment around and protects H.pylori from acidity of stomach.

2. Mucinase and flagella allow the organism to migrate through thick mucus layer that cover stomach epithelial cells.

3. Vacuolating cytotoxin-A(Vac-A): it induces formation of vacuoles (vacuolation) in cytoplasm of eukaryotic epithelial cells.

4. Cytotoxin-associated gene-A(Cag-A) that destroys the epithelial cells and induce inflammatory response.

Source and Transmission : Natural habitat is human stomach. The organism is found deep in mucous

layer near the epithelial cells surface. Mode of transmission is not completely clear. It is probably acquired by

ingestion or probably transmission from person to person. Pathogenesis:

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The Pathogenesis is dependent on ability of H. pylori to acid-tolerance and on rapidly motile.

It attaches to and colonize mucus-secreting epithelial cells of gastric mucosa in stomach and duodenum, but does not colonize the rest of intestinal epithelia.

Mucinase allow the organism to migrate through thick mucous layer that cover stomach epithelial cells.

Toxins may damage the mucosal cells. Vac-A destroys and damage the mucin-producing epithelial cells(mucosa epithelia), and formation of vacuoles in cytoplasm of infected epithelial cells.

Cag-A is potential in ulceration and carcinogenesis. Combination of lowered mucous production with inflammatory response, leads to damage to mucosal epithelia and area of ulceration. The loss of protective mucus coating predisposes to gastritis and peptic ulcer.

Disease and clinical findings: H.pylori causes acute antral gastritis, gastric ulcer, duodenal(peptic) ulcer and

gastric cancer. Acute gastritis and peptic ulcer are characterized by nausea, vomiting, fever,

and upper abdominal pain. In chronic ;stomach pain, nausea, bloating, belching , sometime vomiting and black stool. More than 80% of individuals infected with HP are asymptomatic.

Individuals infected with HP have 10-20% risk developing peptic ulcer and 1-2% risk of acquiring stomach cancer. Inflammation of pyloric antrum is more likely to lead to doudonal ulcer whereas inflammation of corpus body is more likely to lead to gastric ulcer and gastric carcinoma.

Infection is common in adults, but rare in children. Lab. Dx

Histological examination for gastric biopsy. H.pylori can be cultured on Skirrow medium. Urease test is important in an

identification. Blood collection for determination of specific antibodies in serum. ELISA

also used for serum antibodies. Treatment:

Combination therapy(triple therapy)is required. Amoxicillin plus clarithromycin plus proton-pump inhibitors ,such as omeprazole, or combination of bismuth plus metronidazole and either amoxicillin or tetracycline.

Prevention: Acid-suppressing agent and urease inhibitors enhance healing of infection. No vaccine is available.

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