Infections of gastrointestinal tract (Diarrhea, gastroenteritis, dysentery, food poisoining)

Gastrointestinal Infections
Uday Sharma
MSc. clinical microbiology

1. Uday Infections of Gastrointestinal Tract

2. Various gastrointestinal infections include Diarrhea Gastroenteritis Dysentery Food poisoning

3. Diarrhea Diarrhea is defined as passage of three or more loose or liquid stools per day, in excess than the usual habitat for that person (World Health Organization). May be caused by microbial infections, or as a result of other gastrointestinal diseases such as inflammatory bowel diseases, coeliac disease, etc Traveler's Diarrhea M ost common travel-related infectious illness Occurs in about 20-50% of people traveling from temperate industrialized countries to tropical regions of Asia, Africa, and Central and South America Characterized by a sudden onset of abdominal cramps, anorexia, and watery diarrhea

4. Infectious agents and mechanism of diarrhea:

5. Etiological agents of travelers diarrhea

6. Gastroenteritis Aka infectious diarrhea Defined as the inflammation of the mucous membrane of stomach and intestine resulting in combination of diarrhea, vomiting and pain abdomen with or without mucus/blood/fever/ dehydration

7. Dysentery Characterized by diarrhea with increased blood and mucus, often associated with fever, abdominal pain, and tenesmus (a feeling of incomplete defecation)

8. Food Poisoning Food poisoning refers to an illness acquired through consumption of food or drink contaminated either with microorganisms, or their toxins Example: Staphylococcal enterotoxin, enterotoxigenic E. coli, Clostridium spp.

9. Etiologic agents of food poisioning

10. EPIDEMIOLOGY Worldwide, about 1.7 to 5 billion cases of diarrhea occur per year, with 1.26 million deaths Second leading cause of death globally More common in developing countries, where young children get diarrhea on an average three times a year

11. Pathogenesis lnoculum Size The dose of infection differs for different pathogens: For example: Shigella, enterohemorrhagic E. coli, Giardia, or Entamoeba: 10-100 bacteria or cysts Vibrio cholerae: 10 5 -10 8 bacilli Salmonella: 10 3 -10 5 bacilli

12. Adherence Adherence to intestinal mucosa is necessary for the organisms to compete with the normal bowel flora and thereby colonizing the intestinal mucosa Crucial for the pathogenesis of many diarrheal agents such as Enteropathogenic E. coli, enterohemorrhagic E. coli, enterotoxigenic E. coli and V. cholerae

13. Toxin Production Enterotoxins: Cause watery diarrhea by acting directly on secretory mechanisms in the intestinal mucosa Cytotoxins: Cause destruction of mucosa! cells, leading to inflammatory diarrhea Neurotoxins: Act directly on the central nervous system producing vomiting.

14. Invasion In addition to producing cytotoxins, bacterial invasion is another mechanism by which destruction of intestinal mucosal cells takes place resulting in diarrhea

15. Host Factors Alterations of the host defense mechanisms can promote the diarrheal diseases. Suppression of the normal flora Neutralization of gastric acidity: Promote the acid labile pathogens (e.g. V. cholerae) Inhibition of intestinal motility: Interfere with the clearance of bacteria from small intestine Impaired host immunity Genetic determinants: Host genetic variation influences susceptibility to diarrheal diseases People with blood group O show increased susceptibility to disease due to V. cholerae, Shigella, E.coli 0157, and Norovirus.

16. LABORATORY DIAGNOSIS Specimen Collection Fecal specimen (containing mucus flakes) is collected in a sterile screw capped wide mouthed container In carriers, a rectal swab may be collected In food poisoning outbreaks, vomitus, stool or the suspected food materials are the ideal specimens. The food material should be homogenized or washed thoroughly in sterile diluent, e.g. Ringer's solution.

17. Microscopy Wet mount preparation in saline or iodine is done for detection of pus cells, RBCs and detection of parasitic cysts, trophozoites, eggs or larvae Hanging drop preparation: It is done for liquid specimens to demonstrate darting motility of Vibrio cholerae; which can be further confirmed by inhibition of motility by adding H-antisera

18. Gram-stained smear: Gram-staining is not routinely done because of presence of normal flora in feces. It is recommended only in special situations where the typical morphology would suggest preliminary clue for diagnosis: • Presence of comma-shaped bacilli: Vibrio cholerae • Budding oval yeast cells in immunocompromised host or infant-suggestive of Candida species

19. Acid fast staining can be carried out for detection of oocysts of Cryptosporidium, Isospora and Cystoisospora Electron microscopy for detection of morphology of specific viruses causing gastroenteritis Rotaviruses appear as spokes grouped around the hub of a wheel Astroviruses have star-like morphology Coronaviruses have cup-like depressions on the capsid surface.

20. Bacterial Culture Fecal specimen should be inoculated onto the following media • Enrichment broth: Selenite F broth and alkaline peptone water • Mildly selective medium: MacConkey agar • Highly selective medium: DCA(deoxycholate citrate agar), XLD (xylose lysine deoxycholate) agar and TCBS (thiosulfate citrate bile salt sucrose) agar.

21. Identification: Appropriate biochemical tests serotyping Antimicrobial susceptibility test

22. Tissue Culture F or the detection of enteric viruses and also for some diarrheagenic E. coli Enterotoxigenic Escherichia coli (ETEC) penetrates HeLa and HEp-2 cell line, where- as verocytotoxin of enterohemorrhagic Escherichia coli (EHEC) is detected by its cytotoxic effect on Vero cell line. Antigen Detection ELISA and rapid tests (e.g. latex agglutination) based antigen detection e.g. detection of antigens of rotavirus, Entamoeba histolytica, Giardia and Cryptosporidium in stool.

23. Molecular Methods Polymerase chain reaction (PCR) assays Toxin Detection ELISA-based formats are available for detection of enterotoxins in stool PCR for detection of genes coding for enterotoxins