Microbiology of the GI tract Flashcards
Where is most of the normal gut flora found in the GI tract?
Colon
What are the roles of the normal gut flora? (4)
- produce vitamins - vitamin B12, vitamin K, thiamine
- stimulate GALT
- stimulate natural antibody production
- prevent colonisation of pathogens and kill non-indigenous bacteria - bacteriosides and outcompete for space
What bacteria present in the GI tract can form protective endospores?
bacillus anthrax
clostridium tetani
How can bacteria stick to GI tract surfaces
Pili and slime
What are obligate anaerobes and aerobes? give examples
Obligate aerobes need oxygen to survive - so cant survive in colon or small bowel. examples are TB and pseudomonas
Obligate anaerobes die in the presence of oxygen - e.g. clostridium (but it can form protective spores so can survive in GI tract)
What are faculatative anaerobes? examples
perfer oxygenated environment but can live without
examples:
gram neg enteric e.g. E. Coli
Where in the GI tract are anaerobic environments?
Colon, small intestine and tongue, deep in taste buds, biofilm between teeth and gingival crevice areas
What pathogens can be found in the mouth? what can they cause?
Bacteria
Streptococcus mutans - aerobic gram positive - dental caries and gingivitis (plaque)
Staphylococcus aureus - aerobic gram positive - parotitis
Lactobacillus - aerobic gram positive
Enterococcus
Fungus:
Candida albicans - oral thrush
What pathogens can be found in the nose?
Streps and Staphs
Where in the body is MRSA screened?
nose, throat and peritoneum - where staphs are usually found
What pathogens can be found in the throat? What can they cause
Strep viridans is found in everyone and is normally fine but dental procedures and general anaesthetic can cause strep viridans bacteraemia
Strep pyogenes - tonsilitis (most cases are viral - adenovirus, rhinovirus, EBV)
Strep pneumoniae - community acquired pneumonia
staph A - parotitis
neisseria meningitidis
haemophilus influenza - community acquired pneumonia
lactobacilli (normally makes vagina acidic so candida albicans cant grow)
corynebacterium diptheriae
candida albicans - thrush
what pathogens can be found in the throat? what do they cause?
H pylori -> gastroduodenal ulcers
What pathogens constitute the normal flora of the colon?
Bacteroides fragilis bracteroides oralis bacteroidesmelaninogenicus E. Coli - most common cause of UTI enterococcus faecalis - second most common cause of UTI
other gram negative enteric bacilli Psseudomonas Shigella Klebsiella Proteus Vibrio cholera Campylobacter Salmonella
Why is gut surgery seen as dirty surgery?
Massive presence of bacteria -> high risk of wound infection therefore must give antibiotics prophylactically that covers anaerobes, gram negative bacilli and gram positive bacilli
Give metranidazole - kills anerobes, and wide-spectrum antibiotics - cephalosporin or gentamicin
What is fecal peritonitis
faecal matter in peritoneum -> high mortality rate due to massive presence of bacteria in peritoneum
What is a perianal abscess
Glands in the anal canal gets infected -> abscesses around the anus
What is the normal flora of the vagina? How is it protective?
Lactobacillus converts glycogen into lactic acid providing an acidic environment and preventing other pathogens from growing
What bacteria exists on the perineal skin
e. coli, enterococcus faecalis and lactobaccillus as they can survive in O2 are present on the perineal skin
whereas bacteroides cannot survive in O2 -> not present
Why are UTIs more common in women
Shorter distance between urethra and anus
What is the most common cause of UTIs?
E. Coli
then enterococcus faecalis
then gram negative enteric bacilli
What GI tract infection can C. diff cause?
pseudomembranous colitis - often arises after antibiotic rteatment in hospital as antibiotics clear normal gut bacteria - less competition for space - also C. diff produce spores which are present in hospitals
What GI tract infection does C. perfringens cause?
Wet/gaseous gangrene - anaerobic digestion of glucose -> ethanol and CO2 so fluid plus gas -> gangrene
Yearly epidemics of viral infections leading to D&V are most commonly caused by which virus?
Noro-virus
Which organisms most commonly cause food poisoning i.e. gastroenteritis-> D&V?
Salmonella, Campylobacter, Listeria
What organism is responsible for causing Cholera?
Vibrio Cholerae - sruvives in water supplies and has a very specific effect on the ileum, leading to massive movement of water and sat into the lumen by active secretion -> severe diarrhoea - rice water appearance (intestinal mucous)
WARNING - SEVERE DEHYDRATION
What are some intestinal parasites (not bacteria or viruses) that cause gastroenteritis?
Giardia and crytposporidium
helminth (worms) -> malabsorption
What is the difference between bacteraemia and septicaemia?
Bacteraemia - bacteria are rapidly cleared from bloodstream by liver or spleen macrophages
Septicaemia - bacteria are not cleared and multiply in the blood stream
What is traveller’s disease? What’s it caused by?
Traveller’s disease is caused by ETEC - enterotoxinogenic E. Coli which produces heat stable or labile toxins which results in severe cholera-like water diarrhoea
Not usually contagious and no inflammation
