0213 - Normal gut Flora Flashcards
Describe key parameters that dictate where bacteria live in the GI tract.
Oxygen - Aerobic or anaerobic (facultative or obligate).
Temperature - Mesophiles grow optimally at 20-45 degrees.
pH - Most grow in pH 5-8, and so are killed in acidic environment of stomach. Alkalo-and acido-philes cannot generally grow in neutral pH.
What type of bacteria are capable of colonising the stomach?
Very few, mainly facultative anaerobes, Gram-positive bacilli and cocci. e.g. Lactobacillus, Strep. sp.
Describe the normal flora of the small intestine.
Very few organisms in duodenum due to gastric juice, bile, and pancreatic secretions. Flora increases in Jejunum and Ileum, begins to resemble the colon due to more alkalinic pH - manily anaerobes, some facultative (Bacteriodes sp., Enterobacteriaceae fam.)
Describe the normal flora of the large intestine.
Largest bacterial community in the body. 1-5% facultative anerobes (e.g. Lactobacillus, Strep spp, Enterobacteriacea fam.) 95-99% are anaerobes (e.g. Bacteriodes, Clostridium spp). Anaerobic, so ferment inside the colon.
What happens to normal flora as you move from mouth to anus?
Numbers and complexity of organisms increase. Colon has highest density and complexity.
How do normal flora develop through the first years of life?
Infant gut born sterile, and bacteria are delivered by food (affected by mode of delivery, feeding type, and antibiotics). Gut flora resembles that of cohabitating adults by around 2 years.
What are the two phyla that dominate the adult gut?
Firmicutes and Bacteroidetes.
Recall some of the beneficial roles microbes play in health
Digestion - extract, synthesise, and absorb nutrients and metabolites including bile acids, lipids, AAs, vitamins, and short-chain fatty acids. Also correlates (in mice) with reduced gut motility, peristalsis, and mucosal and muscle cell turnover.
Immunity - bile acids and SCFAs are anti-inflammatory, differing levels of bacterially-derived vitamins or AAs can influence immune function, and germ-free mice have reduced levels of antibodies. Also ‘crowd out’ pathogenic bacteria.
Describe Clostridium Difficile and it’s infection.
Gram-positive, spore-forming anaerobic bacillus. Opportunistic infection following antibiotics allow it to colonise intestine and release toxins, causing mucosal injury and leakage, diarrhoea, pseudomembranous colitis, toxic megacolon and death. Treated by faecal microbial transplantation.
Describe Bacteroides fragilis and its infection.
Gram-negative, anaerobic bacillus. Highly beneficial commensal flora (break down complex carb, anti-inflammatory properties). However, if intestinal integrity is disrupted, can escape into peritoneum, causing abscesses, bacteraemia, and sepsis.
Describe ways in which the gut microbiota may be altered.
Antibiotics - can eliminate normal flora or pathogens, allowing niche for other pathogens to establish.
Prebiotics - promote growth of beneficial flora
Probiotics - restore population of beneficial gut flora.
Faecal microbial transplantation - into diseased individual.
