2.5 Normal Gut Flora

Question 1

What kind of bacteria can colonise in the stomach and what are the main ones?

Answer 1

Acid tolerant - mainly gram positive bacilli and cocci - facultative anaerobes (lactobacillus and streptococcus species)

Question 2

What prevents colonisation of the duodenum?

Answer 2

inhibitory action of the stomach acid juices, bile and pancreatic secretions

Question 3

What occurs in the distal duodenum in terms of flora?

Answer 3

Starts to resemble the large intestine (pH becoming more alkaline) - mainly anaerobes and some facultative anaerobes (bacteriodes species and Enterobacteriacea)

Question 4

What is the main type of flora in the large intestine?

Answer 4

Mainly anaerobes (some facultative anaerobes)

Question 5

What is an obligate and facultative anaerobe?

Answer 5

Obligate: generates metabolic processes without oxygen consumption

Facultative: use respiration in presence of oxygen and fermentation in its absence

Question 6

By what age do infants have normal gut flora?

Answer 6

2

Question 7

What are the two most common phyla of bacteria in normal flora?

Answer 7

Firmicutes and Bacteroidetes

Question 8

How does the normal flora prevent pathogenic bacteria colonisation?

Answer 8

Normal gut flora will compete for binding space to prevent the pathogenic bacteria from binding

Question 9

What flora changes occur in IBS?

Answer 9

increased Firmicutes:Bacteroidetes ratio and decreased Bifidobacterium

Question 10

What flora changes occur in IBD?

Answer 10

Increased bacterial numbers in mucosa with decreased bacterial diversity

Question 11

What flora changes occur in colorectal cancer?

Answer 11

Increased Fusobacterium species such as E.Coli

Question 12

What flora changes occur in obesity?

Answer 12

Increased Firmicutes:Bacteroidetes ratio with decreased diversity

Question 13

What are prebiotics?

Answer 13

Nutritional compounds used to promote growth of beneficial gut flora

Question 14

What are probiotics?

Answer 14

Bacterial cultures that restore the population of beneficial gut flora

Question 15

What is a fecal microbial transplantation?

Answer 15

Isolation of beneficial bacteria from the fecal matter of healthy donor to replace disrupted populations in diseases individual

Question 16

What are antimicrobials?

Answer 16

They eliminate pathogens or manipulate the normal gut flora to benefit the host

Question 17

How does Clostridium difficile cause diarrhoea and what other complications can it cause?

Answer 17

Antibiotics kill the commensal bacteria allowing for C.difficile to colonise in the intestine
C.difficle will release toxins and cause mucosal injury and leading to mild diarrhoea, pseudomembraneous colitis and toxic megacolon with dilatation of the colon and death

Question 18

What is the role of Bacteroides fragilis?

Answer 18

Helps breakdown complex CHO, promote induction of anti-inflammatory cytokines and help alleviate inflammation

Question 19

What can happen when intestinal integrity is compromised and Bacteroides fragilis is released into the peritoneum?

Answer 19

Abscess
Bacteraemia
Sepsis