GI: Microbiology of the GI tract

Question 1

Where are anaerobic zones in the GI tract?

Answer 1

Parts of the mouth - deep in the taste buds, biofilm between teeth
Small bowel
Colon

Question 2

What are some of the beneficial functions of the gut flora?

Answer 2

• synthesise vitamins eg Vit K and B12
• prevent colonisation of pathogens
• stimulate development of MALT (caecum and peyers patches)
• stimulate production of natural antibodies

Question 3

What MOs are present in the mouth?

Answer 3

Lots of anaerobes - 700 species
Eg streptococci, staphylococci, candida, lactobacilus, enterococcus
Therefore human bites can cause very bad infections
If the individual in malnourished, dehydrated or immunocompromised they can get tissue destruction

Question 4

What are some risk factors for oral thrush?

Answer 4

Not normally a problem but candida in mouth can overgrow:

Diabetics, antibiotics, newborns, immune deficiency

Question 5

What is Ludwig’s angina?

Answer 5

An infected palatine tonsil with strep - drains into neck lymph nodes and into tissues causes laryngeal oedema - need to act v quickly because may stop breathing.

Question 6

What MO causes parotiditis?

Answer 6

Always staph aureus

Question 7

What are some of the flora in the nose?

Answer 7

Staphylococcus and streptococcus

Question 8

What are some flora in the throat?

Answer 8

Everyone has strep viridans (classic cause of sore throat). staphylococci, neisseria meningitidis
Some have H influenzae, candida albicans

Question 9

What can cause bacteraemia and what is a potential complication of this?

Answer 9

Teeth brushing, dental procedures and general anaesthesia can all cause bacteraemia with strep viridans
In healthy people this is only transient but the bacteria can stick to prosthesis and cause infection

Question 10

What are the common bacterial and viral causes of tonsillitis?

Answer 10

70% of cases are viral - adenovirus, rhinovirus, epsetin-barr
30% are bacterial - mainly strep pyogenes

Question 11

What are some common colonic bacteria?

Answer 11

More than 100 species
95% are anaerobes eg clostridial species which can form spores, and bacteroides eg bacteroids fragilis
Also E coli and enterococcus faecalis

Question 12

What are some common perineal organsisms?

Answer 12

E coli, lactobacillus, enterococcus faecalis

Question 13

Why is lactobacillus beneficial to the vagina?

Answer 13

Lactobacillus converts gylcogen to lactic acid to create an acidic environment which prevents other bacteria and candida albicans from growing
If antibiotics are used this can kill lactobacillus which can lead to vaginal thrush

Question 14

What is the most common cause of travellers diarrhoea?

Answer 14

Enterotoxigenic E Coli is the cause in 80% of cases