Microbiology · MU Sofia

111. Microbiological Aspects of Gastrointestinal Tract Infections

Covers gastrointestinal infections, their faecal-oral and food or water routes of spread, and the bacterial, viral, protozoan and helminth pathogens involved, presented in a classification table. It then goes through virulence mechanisms such as adherence, enterotoxins, cytotoxins, invasion and immune evasion, followed by the clinical syndromes each pathogen group produces. Diagnostic tests are summarised in a table, and treatment principles (rehydration first, selective antibiotics and antiparasitics) and prevention measures including vaccines close the note.

Inside: 8 sections · 2 labelled pictures · 2 tables · 16 flashcards · 2 min

Topic 111 of 113 in the MU Sofia syllabus for Microbiology (Medicine, Year 3). The free AceMed note covers it in 8 sections, about 194 words (2 min of reading), with 16 flashcards.

In this note

  1. Microbiological Aspects of Gastrointestinal Tract Infections
  2. I. Overview
  3. II. Classification of Pathogens
  4. III. Pathogenesis and Virulence Mechanisms
  5. IV. Common Clinical Syndromes
  6. V. Diagnostic Methods
  7. VI. Treatment Principles
  8. VII. Prevention and Control

I. Overview

Gastrointestinal tract (GI) infections affect the stomach, intestines, or both, and are a major cause of morbidity and mortality globally. Transmission usually occurs via the fecal–oral route, contaminated food, water, or poor hygiene. Infections may result in diarrhea, vomiting, abdominal cramps, and sometimes systemic illness.

III. Pathogenesis and Virulence Mechanisms

GI pathogens cause disease by:

  • Adherence and colonization: e.g., E. coli with fimbriae
  • Toxin production:
  • Enterotoxins: stimulate secretion (e.g., cholera toxin)
  • Cytotoxins: damage cells (e.g., Shiga toxin from EHEC)
  • Invasion of intestinal mucosa: e.g., Shigella, Salmonella
  • Immune evasion and survival in macrophages: e.g., Salmonella, Yersinia

IV. Common Clinical Syndromes

  • Watery diarrhea: ETEC, V. cholerae, Rotavirus, Norovirus
  • Dysentery (bloody/mucoid stool): Shigella, EHEC, Campylobacter
  • Enteric fever: Salmonella Typhi (systemic symptoms, rose spots)
  • Antibiotic-associated colitis: Clostridium difficile
  • Parasitic diarrhea: Giardia, Entamoeba (greasy or bloody stool)

VI. Treatment Principles

  • Rehydration (oral or IV) is always first priority.
  • Antibiotics only when indicated:
  • Shigella, Typhoid, C. difficile, severe Campylobacter
  • Avoid antibiotics in EHEC to reduce risk of HUS
  • Antiparasitics:
  • Metronidazole for Giardia, Entamoeba
  • Nitazoxanide for Cryptosporidium (immunocompromised)
  • Antiemetics and antidiarrheals: Symptom control only in non-invasive diarrhea.

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