GI Microbiology Flashcards
Outcomes of enteric infections? (4)
diarrhoea, dehydration, malabsorption, repeat infections
Outline water flux including values?
Input 9L - oral intake 2L, salivary, gastric, biliary, pancreatic 7L
Reabsorbed 8.8L - SI 7.5L, LI 1.3L
Excreted 0.2L
Secretion - pulls water into small intestine due to digestion of high osmolar food and active secretion of electrolytes (Cl pump pulling Na pulling water
Absorption - coupled Na/glucose transporter with Na into submucosa attracting water to follow, basis of oral rehydration solutions
4 mechanisms of diarrhoea production?
- Inflammatory - Increased active secretion of electrolyte and therefore water
- Secretory - Damage to brush boarder resulting in malabsorption of nutrients and electrolytes and water goes into bowel
- Osmotic - Damage to brush boarder leading to loss of disaccharide activity and increased osmolarity of stool
- Motility - Altered motility so less time for water reabsorption
Pathogenesis of Vibrio Cholera and type of diarrhoea?
Secretory diarrhoea
Ingested vibrio that aren’t killed by stomach acid adhere to SI enterocytes and release toxin subunit B which binds to receptor and subunit A which alters molecules to enhance adenyl cyclase enzyme resulting in over production on cAMP which overstimulates Cl into lumen, followed by Na, followed by water
Pathogenesis of Shigella and type of diarrhoea?
Inflammatory diarrhoea which is a cause of bacillary dysentery (blood/pus in stool) and inflammatory colitis.
1. M cells engulf shigella and invasion plasmid antigens enter host
2. Ipa protein (actin) cause cells to form filopods which carry bacteria which is released into sub-epithelial tissue
3. Engulfed by macrophages and activated to produce IL1 and attracts PMNL to area which disrupt cell barriers and move into lumen
4. icsA genes on plasmid encode actin to push bacteria into joining cells
5. Damage is caused by inflammatory processes and from cytokines
Single organ infection? (7)
- Liver abscess - pyogenic bacterial from biliary tree/portal circulation/systemic, fungal from candidiasis, helminthic from Echinococcus granulosus, protozoal from entamoeba histolytica (anchovy sauce pus)
- Splenic abscess - from systemic circulation, endocarditis mainly
- Pancreatitis - inflammation mainly from blockage of bile duct and self digestion due to blockage
- Cholangitis - infection of biliary due to blockage of common bile duct or growth of bacteria from duodenum
- Cholecystitis - obstruction of cystic duct or bacteria from duodenum leading to inflammation and infection of gallbladder
- Diverticulitis - sac like projections from colonic wall becoming blocked and infected due to increased pressure or abrasion from food. Local erosion, inflammation, necrosis, perforation
- Appendicitis - narrow lumen easily blocked due to enlarged lymphoid tissue cuased by onstruction leading to luminal wall thickening, bacterial invasion, inflammation and ishaemia, perforation
2 infections due to leakage of gastrointestinal contents?
- Intra-abdominal abscess - develop when leakage is contained by mesentery and classified by location (sub-phrenic/hepatic, paracolic, mesenteric
- Peritonitis - inflammation of peritoneal tissue reacting to blood, bile, urine, gastric fluids and infection.
2a. Primary - spontaneous bacterial peritonitis seen in patients with ascites and end liver disease or CAPD patients
2b. Secondary - usually polymicrobial which is acute (community aquired, perforation, ischaemic bowel), post-op or post-traumatic
2c. Tertiary - in critically ill patients which persists or recurs
What antibiotic covers gram, negative, gram positive, enterococcus and anaerobic organisms
Gram negative - gentamycin
gram positive - vancomycin
enterococcus - amoxycillin
anaerobic - metronidazole
What is the common flora from stomach to colon?
Stomach/duodenum - lactobacilli (gram +ve)
jejunum - lactobacilli, streptococcus
Ileum/appendix/colon - enterbacteria, enterococcus, clostridia, lactobacilli
Alpha vs Beta diversity?
Alpha - mean diversity within a sample group
Beta - diversity between sample groups
Factors affecting a microbiome?
Environment, interactions between microbes, evolution and speciation, stochastic (unpredictable) factors (diet, pharm, geography, lifecycle, birthing process, infant feeding, stress)
What is dysbiosis and what are disorders due to it?
Imbalance in microbial community associated with disease. Due to overgrowth of commensals, loss of commensals, loss of diversity and can lead to atherosclerosis, obesity, IBD, diabetes, neurodegeneration, autoimmune, colon cancer, metabolic changes
Interventions to impact microbiota? (3)
- Prenatal - placenta
- Neonatal - delivery, gestational age
- Postnatal - feeding, geographic location, family members, maternal diet
Hepatitis A: transmission, epidemiology, vaccine, diagnosis, treatment
Faecal-oral route, found worldwide with epidemic areas, risk group in Australia (MSM, IVDU, child-care, travellers). Vaccine very effective with lifelong protection. Diagnosed by IgA for acute (lasts 6-9 mo.) and IgG for immunity after natural infection
Hepatitis E: transmission, epidemiology, vaccine, diagnosis, treatment
enteric transmission in contaminated food and water with illness similar to HAV (jaundice, neurological, DIC in pregnancy) but no vaccine in Australia
