Prebiotics and Probiotics

Question 1

What is Probiosis?

Answer 1

• Introduce large quantities of ‘beneficial’ bacteria into the host (e.g) oral consumption
• take orally
• Probiotics are not commensal parts of the existing microbiota, they are exogenous, from external parts

Question 2

What is a probiotic?

Answer 2

Live organisms (bacteria or yeast) which when administered in adequate amounts confer a beneficial effect on the overall health of the host

Question 3

How do probiotics work?

Answer 3

• Colonization resistance: something commensal microbiota will do, theory that if probiotic establish themselves within the host can have similar effects: take up available space and nutrients within the hosts site and therefore exclude potential pathogens – inhospitable
• Metabolic effects, bacteriocins, producing lactic acid (decreasing pH), making it inhospitable for pathogens and preventing the growth
• Maintain barrier function – probiotics have been shown to increase expression of genes in association with tight junctions (stopping things passing through the layer)
• Also some evidence to suggest probiotics can repair barrier function, also increase mucus secretion therefore adding to barrier function
• Other evidence to suggest they interact with host signalling pathways, and they can increase/decrease cytokine expression, inhibit apoptosis of cells. Disadvantage is, not all mechanisms are determined in healthy human hosts – mainly done in vitro in preclinical labs

Question 4

What are the 2 typical probiotic species?

Answer 4

1. Bifidobacterium spp.

2. Lactobacillus spp.

Question 5

What is Bifidobacterium spp.?

Answer 5

• Typical commensal of the gut of mammals
• Resistance to bile salts
• Obligate anaerobe, non-motile

B. infantis
B. bifidum
B. animalis

Question 6

What is Lactobacillus spp. ?

Answer 6

• gram positive rod
• Part of healthy human microbiota (vagina, gut, sometimes in mouth)
• Produce acids from carbohydrate fermentation
• lactic acid bacterium

L. acidophilus
L. reuteri

Question 7

What is prebiosis?

Answer 7

• Provide the bacteria already present with dietary adjuncts that will selectively feed the beneficial bacteria causing an increase in their numbers

Question 8

What is a prebiotic?

Answer 8

• A substrate that is selectively utilised by host microorganisms conferring a health benefit
• Substrate could be from a whole food, fortified (added to foods), or supplement
• Prebiotics rely heavily on metabolism by colonic bacteria, so a prebiotic cannot be a viable microorganism or antimicrobial. It is a substrate, functional food
• Selective use that results in a benefit to the host
• Like a probiotic, you need these in a adequate quantity to see health benefits and in the absence of negative side effects like excessive gas formation

Question 9

What does breast milk contain?

Answer 9

• Fructo-oligosaccharides (FOS)
• Galacto-oligosaccharides (GOS)
• Known to cause enrichment of bifidobacteria and lactobacilli

Question 10

What should the ideal prebiotic do?

Answer 10

• Want it to reach the distal part of the gut – do not want it to be broken down by eukaryotic or host enzymes
• Want it to survive transit through the upper parts of the digestive system
• Want it to be selectively fermented by members of the intestinal microbiota e.g. bifido bacteria will be able to increase the concentration of beneficial bacteria which may lead to the production of short chain fatty acids, lactic acid etc
• Bifido bacteria cannot break down oligosaccharides
• Need something that can ferment
• If you are fortifying foods or using a supplement, you want them to be stable

Question 11

What is lactulose?

Answer 11

(prebiotic) ‘
- Capable of enriching bifido bacteria in the adult host and reaches distal part of gut where it is selectively fermented.
- Can also act as an osmotic laxative by dropping the pH in the intraluminal space, increase in osmolarity – laxative effect.

Question 12

What does lactulose do when taken in hepatic encephalopathy?

Answer 12

• The production of ammonia, phenol as a result of bacterial metabolism
• Poor liver function means accumulation and eventual BBB crossing
• Lactulose clinical utility in decreasing ammonia levels

Question 13

What does inulin do?

Answer 13

• Increase in bifidobacteria and Anaerostipes spp.
  
  • Increased SCFA production
• Concomitant Bilophila spp. reduction
  
  • Hydrogen sulphide producers
  • Improved gut barrier function (animal model)
• Increased stool frequency

Question 14

Is the term prebiotic recognised by the FDA?

Answer 14

The term prebiotic is not a recognised term by the FDA due to little regulation
In the EU, prebiotics discovered after 1997 is considered novel – has to be cleared