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The Normal Human Microflora - Coggle Diagram
The Normal Human Microflora
The normal human microflora
Normal microflora - microbes that are routinely found at a particular body site
Body contains >10x more bacterial cells
Some parts normally sterile e.g blood, CSF, brain
Others support bacteria e.g gut, skin, mouth nose, vagina
population levels relate to local moisture and nutrient availability
Other species transiently occupy these areas
What happens to acquired microbes
Most will be eliminated/fail to colonise
Some will become part of the normal microflora
Some will cause disease
Acquisition of normal microflora
Acquired during and shortly after birth
Most microbial species present in adults acquired in the first two weeks of life
Once established, composition of normal flora is relatively stable
If disturbed, usually re-establishes key genera in the area quickly
Distribution of normal microflora
SKIN
Averages over 100 species
Mostly Gram +ve.
Staphylococci, Micrococci, Corynebacteria, Propionibacteria.
Approx 10^2 - 10^6 bacteria per cm^2.
Moist areas have highest numbers.
Salt + low pH + microbial secretions help stop other species from colonising
GUT
Over 500 species
Anaerobes + facultatives
Different species occupy different parts
Composition of gut flora changes with age/diet
Approx 10^10 bacteria per g of faeces
Small intestine (duodenum, jejunum, ileum)
Lactobacilli, streptococci, enterococci, yeasts
e.g candida
Large intestine
(colon)
Strict anaerobes/facultative anaerobes
e.g bacteroides, clostridia, bifidobacteria, enterobacteriaceae
e.g E. coli
ORAL CAVITY
Streptococci, actinomyces, aerobes and anaerobes
e.g candida spp
A symbiotic relationship
We provide
A home
Food
Protection + opportunities for dissemination
They provide
Assistance with digesting food
Help maintain local microclimate
Low level stimulation of immune system
Occupy niches thus keeping more pathogen strains out
Beneficial activities of normal microflora
Suppress
growth
of and
block
attachment of other potentially
pathogenic microbes
Provide essential
nutrients
e.g organic acids, vitamin
B7
biotin and vitamin
K2
Enhance
carbohydrate
digestion and
ion absorption
Low level antigenic
stimulation
of the
immune response
The relationship can break down
Many
commensal species
can
become opportunistic pathogens
Can be
reservoirs
for bacterial virulence factors + antibiotic resistance genes
We can
change
the
microflora
Uses of studying composition of normal microflora
Help identify infections following injury
Eliminates certain causative organisms
Identify factors produced by normal microflora which inhibit other microbes
Identify bacteria associated with other host physiological responses
Identify probiotic organisms