9. Microbiology of the Gastrointestinal Tract

Question 1

What are the beneficial roles of normal flora in the GI tract?

Answer 1

Synthesise and excrete vitamins (K, B12, thiamine), prevent colonisation by pathogens (space, bacteriosides), kill non-indigenous bacteria (bacteriosides), stimulate development of GALT, and stimulate production of natural antibodies.

Question 2

What are obligate aerobes?

Answer 2

Must have oxygen to survive.

Question 3

What is an example of a gut flora obligate aerobe?

Answer 3

Pseudomonas or mycobacterium TB.

Question 4

What are obligate anaerobes?

Answer 4

They die in the presence of oxygen.

Question 5

What is an example of a gut flora obligate anaerobe?

Answer 5

Bacteroides fragilis, clostridial organisms.

Question 6

How do clostridium spp survive in aerobic environments?

Answer 6

They form a protective spore.

Question 7

What are facultative anaerobes?

Answer 7

They prefer oxygen but can live without it.

Question 8

What is an example of a gut flora facultative anaerobe?

Answer 8

Gram negative enteric like E. coli, or gram positive skin-dwellers like staphylococcus.

Question 9

What are the anaerobic zones of the GI tract?

Answer 9

Parts of mouth - tongue deep in taste buds, biofilm between teeth, gingival crevice areas. Small bowel. Colon.

Question 10

What are the gram positive aerobic cocci in the GI tract?

Answer 10

Staphylococci, strpetococci, enterococci.

Question 11

What are the gram negative aerobic cocci in the GI tract?

Answer 11

Neisseria meningitides, and neisseria gonorrhoeae.

Question 12

What are the gram negative aerobic bacilli in the GI tract?

Answer 12

Corynebacterium (diphtheria), bacillus (anthrax), mycobacterium TB (acid fast).

Question 13

What are the gram negative anaeobic bacilli in the GI tract?

Answer 13

Clostridia (tetani, perfringens, difficile).

Question 14

What are the gram negative aerobic enteric bacilli in the GI tract?

Answer 14

E.coli, pseudomonas, proteus, klebsiella, salmonella, shigella, vibria cholerae, campylobacter, helicobacter pylori.

Question 15

What are the gram negative aerobic non-enteric bacilli in the GI tract?

Answer 15

Haemophilus influenzae, bordetella pertussis, brucella.

Question 16

What are the gram negative anaerobic bacilli in the GI tract?

Answer 16

Bacteroid fragilis.

Question 17

What are the common anaerobic bacteria of the mouth?

Answer 17

Streptcocci, staphylococci, candida, lactobacillus, enterococcus.

Question 18

What does streptococcus mutans cause in the mouth?

Answer 18

Denta caries/ gingivitis.

Question 19

What does staphylococcus aureues cause in the mouth?

Answer 19

Parotitis.

Question 20

What can candida albicans cause in the mouth?

Answer 20

Oral thrush.

Question 21

What is noma/ cancrum oris?

Answer 21

Anaerobic bacteria causing tissue destruction in the mouth of malnourshied, dehydrated, immunocompromised, or systemically unwell patients.

Question 22

What are the common bacteria of the nose?

Answer 22

Staphylococcus and streptococcus.

Question 23

What are the three screening sites for MRSA swabs?

Answer 23

Nose, throat, and perineum.

Question 24

What are the throat bacteria and fungi?

Answer 24

Streptococcus viridans, streptococcus pyogenes, streptococcus pneumoniae, staphylococci, neisseria meningitidis, haemophilus influenzae, lactobacilli, corynebacterium diptheriae, candida albicans.

Question 25

How does strep. viridans enter the blood stream?

Answer 25

It is in 100% of people in their throats, when teeth are brushed, or in dental procedures, or general anaesthesia, the non-pathogenic throat commensal can enter the blood.

Question 26

What can strep. pyogenes cause?

Answer 26

Tonsillitis, only 30% of cases, other 70% is viral.

Question 27

What is strep. pneumoniae a cause of?

Answer 27

Community acquired pneumonia, accounts for 30% of cases.

Question 28

What is haemophilus influenzae a cause of?

Answer 28

Community acquired pneumonia, accounts for 13% of cases.

Question 29

What is the purpose of lactobacilli in the vagina?

Answer 29

Makes vagina acidic so candida albicans can't grow, so prevents thrush.

Question 30

What are the viral causes of tonsillitis?

Answer 30

Adenovirus, rhinovirus, epstein-barr virus (EBV).

Question 31

What is the stomach bacteria that infects at least half the world?

Answer 31

Helicobacter pyloris.

Question 32

What percentage of those infected with H. pylori develop gastric/ duodenal ulcers?

Answer 32

10-20%.

Question 33

What percentage of duodenal and gastric ulcers is H. pylori associated with?

Answer 33

90% of duodenal ulcers, 70% of gastric ulcers.

Question 34

What are the common anaerobe species in the colon?

Answer 34

Bacteroides and clostridial species.

Question 35

Which bacteria are always present in the colon?

Answer 35

Bacteroides fragillis, bacteroides oralis, bacteroides melaninogenicus, E. coli, entercoccus faecalis.

Question 36

What are the top two causes of UTIs?

Answer 36

E. coli, and enterococcus faecalis.

Question 37

What are the gram negative enteric bacilli that are sometimes present in the colon?

Answer 37

Pseudomonas, proteus, klebsiella, salmonella, shigella, vibrio cholera, campylobacter.

Question 38

What is a major difference between the colon and small bowel in terms of bacteria?

Answer 38

It is normal for the colon to have lots of bacteria, but abnormal for the small bowel to.

Question 39

Why is gut surgery viewed as dirty surgery?

Answer 39

There are so many bacteria so a high risk of wound infection.

Question 40

How is the risk of surgical wound infection reduced with gut surgery?

Answer 40

Antibiotics are given prophylactically.

Question 41

What must the prophylactic antibiotics given for gut surgery be able to cover?

Answer 41

Anaerobes, gram negative bacilli and gram positive bacilli.

Question 42

What are the prophylactic antibiotics normally given for gut surgery?

Answer 42

Metronidazole for anaerobes, and broad spectrum antibiotics like gentamicin or cephalosporin.

Question 43

Why has faecal peritonitis got a high mortality rate?

Answer 43

Due to the huge numbers of bacteria that are now floating free in the peritoneum.

Question 44

What is a perianal abscess?

Answer 44

Glands in the anal canal that produce mucus for lubrication to aid with passing faeces are infected and abscess around the anus.

Question 45

What is a normal vaginal gram positive bacilli bacteria?

Answer 45

Lactobacillus.

Question 46

How does lactobacillus create an acidic environment for the vagina?

Answer 46

It converts glycogen into lactic acid.

Question 47

Which of the following could be present in perineal skin and why? Bacteroides, E. coli, enterococcus faecalis, lactobacillus.

Answer 47

Bacteroides won't as they can't survive O2. The others all could be present as they can survive in the presence of O2.

Question 48

What is the group of bacteria that cause UTIs?

Answer 48

Gram negative enteric bacilli.

Question 49

What does clostridia tetani cause?

Answer 49

Tetanus.

Question 50

How many neonates die from tetanus each year?

Answer 50

60000.

Question 51

What does clostridia difficile cause?

Answer 51

Pseudomembranous colitis - severe inflammation of the colon.

Question 52

When does clostridia difficile often arise?

Answer 52

After antibiotic use.

Question 53

What does clostridia perfringens cause?

Answer 53

Gas/wet gangrene.

Question 54

How does clostridia perfringens cause gas/wet gangrene?

Answer 54

Anaerobic digestion of glucose leads to ethanol and CO2.

Question 55

What does norovirus cause?

Answer 55

Vomiting and diarrhoea?

Question 56

What does gastroenteritis often follow?

Answer 56

Consumption of food or drink contaminated with organisms or toxins - food poisoning.

Question 57

What is the presentation of gastroenteritis?

Answer 57

Rapid onset or up to 48 hours of ingestion of vomiting and diarrhoea.

Question 58

What are the common causative organisms and toxins of gastroenteritis?

Answer 58

Salmonella, campylobacter, and listeria bacteria. Or toxins from staphylococcus and clostridium.

Question 59

What causes cholera?

Answer 59

Vibrio cholerae.

Question 60

What are the effects of vibrio cholerae on the ileum?

Answer 60

Lead to mass movement of water and salt into the lumen by active secretion leading to serious diarrhoea - rice water appearance from intestinal secretions plus mucus.

Question 61

Why can cholera be life threatengin?

Answer 61

Rapid, severe dehydration following the severe diarrhoea can be life threatening.

Question 62

How is cholera managed?

Answer 62

Replace lost water and electrolytes with appropriate replacement fluids.

Question 63

What are some parasite causes of gastroenteritis?

Answer 63

Giardia and cryptosporidium protozoans.

Question 64

What can helminth infections of the intestines lead to?

Answer 64

Malabsorption as well as other things.

Question 65

What is bacteraemia?

Answer 65

Bacteria are rapidly cleared from the bloodstream by liver and spleen macrophages so no symptoms.

Question 66

What is septicaemia?

Answer 66

Bacteria are not cleared and multiply in the blood stream. Sepsis symptoms develop.

Question 67

What is ETEC?

Answer 67

Enterotoxinogenic E. coli.

Question 68

What does ETEC cause?

Answer 68

Travellers' diarrhoea in developing countries.