Gastrointestinal Tract Micro Flora Quiz

Introduction to Gastrointestinal Microflora

• Human beings host a diverse array of microorganisms, primarily residing in the gastrointestinal tract (GIT).
• The GIT mucosa, a single layer columnar epithelium approximately 0.1 mm thick, covers an estimated area of 300 m² and supports over 700 microbial species.
• The human fetus is initially sterile until exposure to external environments during birth.

Definition and Types of Microflora

• Normal microbial flora refers to microorganisms inhabiting healthy individuals' skin and mucous membranes.
• Resident flora are stable and can reestablish if disturbed, while transient flora are only temporarily present and may be pathogenic.

Factors Influencing Microflora

• The distribution of microorganisms along the GIT is influenced by environmental, microbial, and host factors.
• Physiological perturbations (e.g., varying pH levels) can affect microbial growth, as seen with Salmonella typhimurium.
• Epithelial receptor expression can change based on the health status of the individual.

Physiological Importance of Gastrointestinal Microflora

• Normal flora perform various essential functions, including:
  • Metabolic Functions: Produce vitamins like K and B, and short-chain fatty acids.
  • Infection Prevention: Compete for nutrients and space, producing toxic metabolites to inhibit pathogen colonization.
  • Immune System Priming: Germ-free animals show poorly developed immune systems, emphasizing microbial benefits.

Probiotics and Prebiotics

• Probiotics are live microorganisms providing health benefits, effective against dysbiosis, IBS, IBD, and antibiotic-associated diarrhea.
• Prebiotics are non-digestible ingredients that stimulate beneficial bacteria, aiding gut health and used in treatments like fecal microbiota transplantation for C. difficile infections.

Clinically Important Microbes in GIT

• The oral cavity contains both facultative and strict anaerobes; Streptococcus mutans is notable for its cariogenic properties.
• The stomach's highly acidic environment (pH 1.5-3.5) limits microbial presence to less than 1000 organisms/mL, impacting microbial survival.

Helicobacter pylori

• A significant pathogen, H. pylori is a Gram-negative bacillus linked to various gastric diseases including gastritis, ulcers, and gastric cancer.
• It employs various virulence factors (e.g., urease, proteases) to establish itself in the gastric mucosa.
• Detection methods for H. pylori include invasive techniques (gastric biopsy) and non-invasive tests (urea breath and stool antigen tests).

Microbial Distribution in the Small Intestine

• The proximal small intestine hosts limited microbes (<10,000 organisms/mL), primarily lactobacilli and enterococci.
• Peyer’s patches in the ileum detect pathogens and initiate immune responses, while goblet cells maintain mucosal integrity.

Composition of the Colon

• The colon is densely populated with microorganisms (10¹¹ to 10¹² CFU/g of feces), predominantly anaerobes such as Bacteroides and Clostridium.
• The ratio of anaerobic to aerobic bacteria is approximately 100:1, with adult feces consisting of bacteria, sloughed epithelium, and undigested food.

Colitis

• Colitis refers to colon inflammation caused by pathogens either through direct invasion or toxin ingestion.
• Symptoms include purulent and bloody diarrhea, fever, tenesmus, and abdominal pain.