Paper I
Question
Discuss the beneficial effects of normal flora.
Answer
Beneficial effects of normal flora:
- Colonization resistance / competitive exclusion — normal flora occupy available attachment sites and compete for nutrients, preventing colonization and overgrowth by pathogenic organisms (e.g., disruption of gut flora by antibiotics predisposes to Clostridioides difficile overgrowth and pseudomembranous colitis).
- Production of antimicrobial substances — normal flora produce bacteriocins and metabolic products (e.g., lactic acid by vaginal lactobacilli, maintaining an acidic pH that inhibits pathogen growth) that directly inhibit competing pathogenic organisms.
- Nutritional/metabolic contributions — gut flora synthesize essential vitamins (Vitamin K, some B-complex vitamins) and aid in the digestion/fermentation of complex carbohydrates not otherwise digestible by the host, yielding short-chain fatty acids that nourish colonic epithelium.
- Stimulation and maturation of the immune system — normal flora provide continuous antigenic stimulation that promotes the normal development and maturation of gut-associated lymphoid tissue (GALT) and the systemic immune system, particularly important in early life.
- Maintenance of mucosal barrier integrity — normal flora contribute to the maintenance of the epithelial barrier, supporting mucus layer production and epithelial cell turnover.
- Skin protection — resident skin flora (e.g., Staphylococcus epidermidis) help maintain skin pH and provide a physical/competitive barrier against colonization by transient pathogenic organisms.