Lecture 12 Flashcards
each human body hosts
40 trillion microbes
microbiota
= microflora
all microbial species
microbiome
all microbial species and their interactions
resident microbiome
microbes in a healthy human body
where do resident microbiomes occur?
skin, respiratory tract, digestive tract, and urogenital tract
*exposed to environment
where do resident microbiomes NOT occur?
internal organs, blood, lymph, and nervous system
*not exposed to environment
what affects the various resident microbiomes?
O2 levels, acidity (pH), and nutrient availability
different body area = different habitats (microenvironments)
benign effects of microbiomes
no positive/negative effect
occupy human microhabitats
most common
beneficial effects of microbiomes
positive effect
metabolism and defense
occurs some of the time
pathogenic effects of microbiomes
negative effect
cause infectious diseases
occurs only a few times (more rare)
Positive effects of the microbiome
immune system maintenance and development
aids in nutrition (combating obesity depending on microbiome)
aids in neurological functioning
how are resident microbiomes established?
the first exposure is from delivery (vaginal v. c-section)
human interventions for c-section babies (vaginal seeding or bacterial baptism)
continued exposure and prebiotics from breastfeeding
from the environment, thus variable
The uterus is a
sterile environment
- no pre-birth exposure to microbes
- humans are born without a microbiome
how are resident microbiomes maintained?
Clear out a large number of bacteria every day, will grow back
Zones of containment minimize bacteria-epithelial cell contact
outer (general defense) and inner (specific defense) mucous layers
host-pathogen interactions
pathogens live on/in hosts and cause disease
cause disease in the absence of normal host resistance
dysbiosis
imbalanced or impaired microbiome
Skin microbiome
medium surface area (2 m^2) and high microbial diversity (1000 species)
Skin microbiome characteristics
heterogeneous habitat
has multiple microenvironments (sebaceous, moist, and dry)
antimicrobial chemicals present (sweat)
nutrient sources (sebum– oily secretion)
Sebaceous skin microbiome
upper chest
oily areas
moist skin microbiome
armpits
high moisture
dry skin microbiome
forearms
low moisture
Factors affecting the skin microbiome
age and personal hygiene (host factors)
weather (environmental factor)
disruptions of skin microbiome
acne (pore blockage), body odor, and disease
oral cavity microbiome
small surface area (0.2 m^2) and medium microbial diversity (600 species)
primarily anaerobic metabolism
- facultative aerobes and obligate anaerobes
– make a biofilm
oral cavity characteristics
heterogeneous habitat
antimicrobial chemicals present (saliva contains lysozyme)
The nutrient source is food particles and cell debris near gums/teeth
Dental plaques and tooth decay
teeth are made of enamel and the lactic acids produced by certain bacteria break down the enamel
leads to dental caries aka tooth decay
formation of dental caries
tooth surface is easy to clean but gingival crevice is not
preventing dental caries
restrict sucrose intake
brush your teeth
enhance enamel with fluoride
GI tract microbiome
very large surface area (400 m^2) and high microbial diversity (1000 species)
GI tract characteristics
heterogeneous habitat (stomach, small & large intestines)
antimicrobial conditions (low pH in stomach and antibodies in intestines)
nutrient sources (a ton from a high diversity of food intake and processing)
stomach microbiome
highly acidic fluids (pH=2)
only acidophiles can survive
- low diversity
small intestine microbiome
fairly acidic (pH= 4-5)
similar microbiome to the stomach
competition with the microbiome since we absorb our nutrients here
large intestine
neutral (pH=7)
strictly anoxic (No O2- anaerobic)
mainly absorb H2O here so less competition
most diversity (10 to 100 billion cells per gram)
“fermentation vessel”
functions of intestinal microbes
vitamin synthesis (B12 and K) and steriod metabolism (microbes convert)
gas production
Microbiome turnover
10 trillion bacteria are removed each day
- fecal matter is one-third bacterial cells
Remaining bacteria continue to grow
- populations double 1-2x per day
Disrupting the resident intestinal microbiome
diarrhea, alteration of digestive function, and pathogen colonization
Restoring the resident intestinal microbiome
probiotics and fecal microbiota transplant
mucosal tissue microbiome
large surface area (100m^2) and low microbial diversity (60 species)
mucosal tissue characteristics
homogenous habitat (upper v lower respiratory and urogenital tract)
antimicrobial conditions (ex low pH in Vagina)
nutrient sources (mucus secretions)
*low diversity of microbes
Virulence
a measure of pathogenicity
(how much harm it causes measured on a scale)
Pathogenesis
process by which microbes cause disease
adherence, invasion, and infection
Measuring virulence
LD50 (amount of pathogen that kills 50% of host individuals)
low v high LD50
Attenuation
decrease/loss of virulence
often used as vaccines
in nature there is a selection for attenuation
Adherence
attachment to host cells
highly specific to certain cell types
mechanisms: slime layers and capsules & pili
Invasion
entering host tissues and causing damage/disease
most invasion occurs through wounds
infection
growth/production of toxins and virulence factors
Virulence factors
promote colonization and growth of pathogens
ex. toxins, capsules, and pili
toxins
chemicals that inhibit cell function or kill cells
Exotoxins
released from pathogen cells
types: cytolytic (damage to cytoplasmic membrane) and AB ( inhibit internal cell functions)
alpha-toxin
cytolytic toxin
pore in membrane that allows for influx and efflux of various components (causes cell to lyse)
done by staphylococcus spp.
diptheria
AB toxin
binds to receptor protein that stop protein synthesis
done by cornebacterium
endotoxins
not released from pathogen cells
present in LPS of outer membrane
less toxic than exotoxins
ex. salmonella endotoxins
Barriers to infection
physical (skin), chemical (antimicrobial and low/changing pH), and biological (competition w/ resident microbiome)
Risk factors
increase infection susceptibility
risk factors examples:
age, diet, and stress
