1. Non Invasive Enteritis II

2. Barriers to GIT infection:
Stomach acidity (low PH).
Mucus layer and gut motility (peristalsis)→ prevent adhesion The glycocalyx (mucin rich layer) covers the epithelial cells surface→ entrap invading bacteria.
Shedding of mucosal epithelium lining the GIT.
Bile secretion prevent the growth of non-enteric bacteria and enveloped viruses.
M cells (microfold) of Peyer’s patches which have a surveillance function (sampling).
Normal flora of intestinal tract.
Secretory IgA.

3. CEACAM1= carcinoembryonic antigen-related cell adhesion molecule

4. Bacterial enteritis:
Non invasive → multiplication within the lumen and toxin production → watery diarrhea Causative agents:
V. cholerae.
Enterobacteriaceae: Enterotoxigenic E. coli, Enteropathogenic E. coli.
Local invasion → invade and destruct the mucosa and the epithelia → bloody diarrhea. E.g. Shigella and Enterohemorrhagic E.coli, Campylobacter jejuni, Salmonella enteriditis …….
Systemic invasion → Cuasative bacteria can be isolated from the blood; Salmonella Typhi, Brucella.

5. Vibrio cholerae
Vibrionaceae: gram negative rods, curved, motile by single polar flagellum. Alkaliphiles (pH ).
Vibrionaceae family:
Vibrio cholerae → cholera (watery diarrhea).
Vibrio parahaemolyticus.
Vibrio vulnificus.
V. cholerae has ≈ 140 serotypes based on its LPS (O antigen). Serotype O1 is the most common followed by serotype O139.
V. cholerae serotype O1 has 2 biotypes:
Classical.
El Tor.

6. Cholera cause ≈ 3 millions cases and 10000 deaths yearly.
Epidemiology:
Vibrio cholerae O1 biotype classical → 6 pandemics in Asia for centuries.
Vibrio cholerae O1 biotype El Tor was isolated from pilgrims at El Tor station in 1905.It had caused the seventh pandemic in1961.
Infections with the new serotype Vibrio cholera O139 (Bengal) appeared in Bangladesh in 1990 and spread to India and other countries.
Cholera cause ≈ 3 millions cases and deaths yearly. N

7. Pathogenesis and Microbial Virulence:
Transmission:
Source: human cases or carrier Human disease only without animal reservoir.
Waterborne: drinking un-boiled or untreated water.
Foodborne; Contaminated sea food or shellfish.
Fecal-oral route: human carriage (colon) is reported in some cases.
Pathogenesis:
Pathogenic dose: CFU/ml (lower in hypo-chlorohydria).
When vibrios reach ampulla of Vater in the duodenum; surviving organisms are bathed in bicarbonate-buffered pancreatic juice (pH can be as high as 9).

8. Vibrios reach the epithelia of the small intestine by flagella & mucinase enzyme that hydrolyses the mucus.
Adhere to the epithelia of the intestinal tract by type 1 common pili (colonization factor antigen Cfa).
Vibrios stick to each other and establish colonization (micro-colonies) by toxin-co-regulated pili (TCP).
Produce cholera toxin. Cholera toxin (Ctx) binds to the receptor on epithelial cells → stimulate G protein → activate the adenylate cyclase → increase cAMP production → inhibit sodium absorption and increase chloride secretion by enterocytes → ↑NaCl in the lumen→ passive secretion of water → severe watery diarrhea + mucus (the action of the mucinase) → Rice Water Diarrhea. n
TCP: so named because it is synthesis is regulated by the same system that regulates cholera toxin production.

9. Flagella, mucinase, Cfa, TCP

10. Clinical presentation:
Incubation period: 2 hours – 5 days (inoculum size)
Sever watery diarrhea (rice water without faecal matter) and vomiting of clear fluid. No fever Dehydration and electrolytes imbalance (patients may lose liters of fluid/ day) dry mouth and skin; decreased skin turgor.
Deep rapid breathing due to acidosis:
Rapid pulse.
Coma (Na, Cl loss).
Death: 70% if not treated 0.5% with treatment.

11. Rice water diarrhea

14. Laboratory diagnosis: Clinical specimens: stool.
Microscopy (diagnostic in endemic area):
Wet mount: highly motile bacilli which stop moving when we add specific antisera.
Gram stain: Vibrios are gram-negative curved bacilli, motile with a single polar flagellum.
Antigen detection: detect the O1 or O139 antigens or the cholera toxin. N
Darting motility= shooting star

15. Blood agar: usually beta hemolytic (El Tor).
Cultural and isolation (diagnostic in non endemic area i.e. gold standard) :
Media:
Blood agar: usually beta hemolytic (El Tor).
MacConkey's agar: non-lactose fermenting colonies.
Alkaline peptone water: Selective media; pH 8.5-9
TCBS: Thiosulfate-citrate-bile salts-sucrose agar; Selective and differential → change the color from green to yellow.
Biochemical reactions: catalase, oxidase and indole positive and can reduce nitrate to nitrite (cholera red reaction positive).
Vibrio cholerae are grown for 24 hours in peptone water containing adequate amount of tryptophan and nitrate, they produce indole and reduce nitrate to nitrite. On adding a few drops of sulphuric acid, nitroso-indole is formed, which is red in color.

16. Diagnosis
Serotyping and biotyping: Epidemiological purposes.
PCR: detect nucleic acid in the sample.
Treatment:
- Fluid and electrolyte replacement in early stage (life saving). - Antibiotics: Tetracycline or co-trimoxazole.

17. Oxidase Test
Indole Test
Prevention: - Prevent transmission: food and water hygiene & acidification of food. - Vaccines: killed vaccine with recombinant binding subunit of the cholera toxin.

18. Non Cholera Vibrios
Vibrio parahaemolyticus:
Halophilic microbes.
Transmission: consumption of undercooked or raw seafood; shellfish, and crustaceans.
Gastroenteritis: fever, abdominal pain, watery diarrhea some times with blood due to invasive enteritis.
Vibrio vulnificus:
Halophilic vibrio.
Transmission: undercooked shellfish or exposure of wound to salt water.
Invasive enteritis; associated with high mortality rate (septicemia and death).
Wound infection.

19. Flesh eating bacteria (V. vulnificus)

20. Escherichia coli: E. coli groups associated diarrhea: Watery diarrhea:
Enteroaggregative E. coli
Watery toxin mediated diarrhea:
Enterotoxigenic E. coli.
Enteropathogenic E. coli.
Bloody diarrhea due to invasive enteritis:
Enterohemorrhagic E. coli.
Enteroinvasive E. coli.

21. Enterotoxigenic E. coli:
the causative agent of traveler’s diarrhea.
Produce two enterotoxins: Heat labile (LT): activate G protein and adenylate cyclase; ↑cAMP. (same effect of cholera toxin).
- Heat stable (ST): activate guanylate cyclase → watery diarrhea.
Enteropathogenic E. coli:
Cause watery diarrhea in infants.
Adhere to the epithelial cells by Cfa pilus & insert exotoxin Tir (translocation intimin receptor) → brush border damage; malabsorption and watery diarrhea.

22. Ctx: cholera toxin. ST: heat stable toxin. LT: labile toxin
Ctx: cholera toxin. ST: heat stable toxin. LT: labile toxin Cfa: colonization factor antigen.