Medical microbio: the human microbiome Flashcards
Human microbiome
-the collection of all the microorganisms living in association with the human body (microflora, microbiota)
ex number of human cells in the human body.. etc
number of human cells in the human body
~10^13
number of microorganisms in the human body
~10^14
number of genes in the human genome
~20,000
number of genes in the microbiome
~20,000,000
colonization
begins immediately after birth
-diversity of species present varies greatly between individuals
Where does the microbiota live?
- every exposed area of the body is colonized by bacteria like skin and mucous membranes
- internal tissues should be free of microbes: like blood, muscles, organs
what are microbiota doing in the body?
- most are harmless commensals
- few contribute to disease
- many contribute to health:
- produce beneficial products
- inhibit the growth of pathogens
ex. lactobacillus acidophilus protects the female reproductive system
microflora of the skin
- different areas of the skin vary in chemical composition and moisture content
- provides 3 different micro environments: dry skin, moist skin, and sebaceous skin
- each with different microbial populations
dry skin
- (forearms, hands)
- high numbers of betaproteobacteria
- known from 16 rRNA genes
- rarely cultured-no one really knows what they’re doing
- second highest is corynebacteria
- most are harmless commensals, but some may cause skin infections
corynebacterium diphtheria
example of dry skin bacteria
-can case non-healing ulcers of the skin- cutaneous diphtheria
moist skin
(armpits, nostrils)
- high numbers of corynebacteria and staphylococci
- most are harmless commensals : staphylococcus epidermis -most frequently isolated from skin
- some are important pathogens: ex. staphylococcus aureus - cause of boils, abscesses, wound infections
sebaceous skin
(oily skin around the nose, on the upper chest and back)
- high numbers of propionibacteria
- anaerobic actinobacteria that produce propionic acid as as end-product of fermentation
propionibacterium acnes
- sebaceous skin
- lives in hair follicles and eats sebum- oil secreted by skin
- overgrowth can trigger inflammation
- inflammatory acne
microflora of the oral cavity
saliva has antimicrobial enzymes:
- lysozyme
- lactoperoxidase- catalyzes production of superoxide radicals O2-, oxidative damage to invading microbes
- despite this, this mouth is home to a complex microbial community, including aerobes and anaerobes
Neisseria mucosa
microflora of the oral cavity
aerobic
lives on mucous membranes like the tongue
Streptococcus mutans
microflora of the oral cavity
aerotolerant anaerobe
-produces sticky dextran slime layer that lets it stick to surfaces
*forms biofilms in crevices around the teeth
-produces lactic acid as an end-product of fermentation
-degrades tooth enamel
*dental carries (cavities)
-can lead to inflammation along the gum line: gingivitis
microflora of the gastrointestinal tract
-the stomach
the small intestine
the large intestine
Stomach
low pH and proteolytic enzymes make the stomach inhospitable to most microbes
-some bacteria do colonize in the stomach
helicobacter pylori
- microflora in stomach
- colonizes surface of membrane, protected from stomach acids by mucous
- has a number of virulence factors:
- exotoxin-kills cells in the membrane
- endotoxin- triggers inflammation
- cause of stomach ulcers
- treated with antibiotics-tetracycline
the small intestine
- area of rapidly changing pH
- as pH becomes more neutral, bacterial numbers increase
Enterococcus
- small intestine microflora
- genus of Gram positive lactic acid bacteria
- frequent cause of nosocomial infections (ex. blood infections)
- develop antibiotic resistance readily (ex VRE)
- spread resistance genes onto other gram positive bacteria
- horizontal gene transfer
The large intestine
- pH is neutral, environment anoxic
- enormous number of microbes ~10^11 cells/g of feces
- mostly anaerobes and facultative aerobes
- 16S rRNA gene sequences reveal that E. coli probably makes up
E. coli
- large intestine microflora
- most cultured bacterium from feces
- indicator of fecal contamination
- most strains are non-pathogenic
- may stimulate the immune system
- produce vitamin K
role of gut microorganisms in obesity
- studies compared normal mice with germ free mice:
* germ free mice has 40% less body fat - inoculated germ free mice with microbes from healthy mouse intestines
* inoculated mice quickly gained weight - compared the microbiomes of normal weight mice to genetically obese mice
* genetically obese mice had few bacteroidetes, more firmicutes and way more methanogens
- suggested that methanogens use up H2 which promotes bacterial fermentation
- bacterial fermentation makes nutrients available to the host
changing the microbiota of the large intestine can affect human health:
ex. oral antibiotics
- opportunistic pathogens can take over
- Antibiotic associated colitis
antibiotic associated colitis
- clostridium difficile grows
- inflammation of the colon
treatment: further antibiotics, probiotics, Transpoosition
microflora of mucosal tissues
upper respiratory tract
lower respiratory tract
genitourinary tract
female reproductive tract
upper respiratory tract
- home to a variety of bacteria including staphylococci, streptococci, and corynebacteria
- some people harbour pathogens among their normal microflora
- carriers
ex. staphlococcus aureus
lower respiratory tract
no resident microflore
-mucous, lysozyme, ciliated cells, secretory IgA, phagocytes
Genitourinary tract
upper urinary tract (kidneys, bladder)
*normally free of microorganisms
Urethra
*home to some gram negative bacteria
-some members of the normal microbiota can act as opportunistic pathogens when transferred to urinary tract
.e.coli is one of the most common causes of urinary tract infections
female reproductive tract
- lactobacillus acidophilus in the vagina produces lactic acid from glycogen
- lowers pH and prevents growth of other microbes
- if normal microbiota is disturbed (ex. lactobacilli killed by antibiotics): yeasts can grow and cause yeast infections
