Microbiology of the GI tract

Question 1

Where is most of the normal gut flora found in the GI tract?

Answer 1

Colon

Question 2

What are the roles of the normal gut flora? (4)

Answer 2

1. produce vitamins - vitamin B12, vitamin K, thiamine
2. stimulate GALT
3. stimulate natural antibody production
4. prevent colonisation of pathogens and kill non-indigenous bacteria - bacteriosides and outcompete for space

Question 3

What bacteria present in the GI tract can form protective endospores?

Answer 3

bacillus anthrax

clostridium tetani

Question 4

How can bacteria stick to GI tract surfaces

Answer 4

Pili and slime

Question 5

What are obligate anaerobes and aerobes? give examples

Answer 5

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)

Question 6

What are faculatative anaerobes? examples

Answer 6

perfer oxygenated environment but can live without

examples:
gram neg enteric e.g. E. Coli

Question 7

Where in the GI tract are anaerobic environments?

Answer 7

Colon, small intestine and tongue, deep in taste buds, biofilm between teeth and gingival crevice areas

Question 8

What pathogens can be found in the mouth? what can they cause?

Answer 8

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

Question 9

What pathogens can be found in the nose?

Answer 9

Streps and Staphs

Question 10

Where in the body is MRSA screened?

Answer 10

nose, throat and peritoneum - where staphs are usually found

Question 11

What pathogens can be found in the throat? What can they cause

Answer 11

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

Question 12

what pathogens can be found in the throat? what do they cause?

Answer 12

H pylori -> gastroduodenal ulcers

Question 13

What pathogens constitute the normal flora of the colon?

Answer 13

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

Question 14

Why is gut surgery seen as dirty surgery?

Answer 14

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

Question 15

What is fecal peritonitis

Answer 15

faecal matter in peritoneum -> high mortality rate due to massive presence of bacteria in peritoneum

Question 16

What is a perianal abscess

Answer 16

Glands in the anal canal gets infected -> abscesses around the anus

Question 17

What is the normal flora of the vagina? How is it protective?

Answer 17

Lactobacillus converts glycogen into lactic acid providing an acidic environment and preventing other pathogens from growing

Question 18

What bacteria exists on the perineal skin

Answer 18

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

Question 19

Why are UTIs more common in women

Answer 19

Shorter distance between urethra and anus

Question 20

What is the most common cause of UTIs?

Answer 20

E. Coli

then enterococcus faecalis

then gram negative enteric bacilli

Question 21

What GI tract infection can C. diff cause?

Answer 21

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

Question 22

What GI tract infection does C. perfringens cause?

Answer 22

Wet/gaseous gangrene - anaerobic digestion of glucose -> ethanol and CO2 so fluid plus gas -> gangrene

Question 23

Yearly epidemics of viral infections leading to D&V are most commonly caused by which virus?

Answer 23

Noro-virus

Question 24

Which organisms most commonly cause food poisoning i.e. gastroenteritis-> D&V?

Answer 24

Salmonella, Campylobacter, Listeria

Question 25

What organism is responsible for causing Cholera?

Answer 25

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

Question 26

What are some intestinal parasites (not bacteria or viruses) that cause gastroenteritis?

Answer 26

Giardia and crytposporidium

helminth (worms) -> malabsorption

Question 27

What is the difference between bacteraemia and septicaemia?

Answer 27

Bacteraemia - bacteria are rapidly cleared from bloodstream by liver or spleen macrophages

Septicaemia - bacteria are not cleared and multiply in the blood stream

Question 28

What is traveller’s disease? What’s it caused by?

Answer 28

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