Medical microbio: the human microbiome Flashcards Preview

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Flashcards in Medical microbio: the human microbiome Deck (32):

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



number of microorganisms in the human body



number of genes in the human genome



number of genes in the microbiome




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:
*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
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



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



-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

1.studies compared normal mice with germ free mice:
*germ free mice has 40% less body fat
2.inoculated germ free mice with microbes from healthy mouse intestines
*inoculated mice quickly gained weight
3.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
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
*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