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Flashcards in Medical microbio: the human microbiome Deck (32):
1

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

2

number of human cells in the human body

~10^13

3

number of microorganisms in the human body

~10^14

4

number of genes in the human genome

~20,000

5

number of genes in the microbiome

~20,000,000

6

colonization

begins immediately after birth
-diversity of species present varies greatly between individuals

7

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

8

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

9

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

10

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

11

corynebacterium diphtheria

example of dry skin bacteria
-can case non-healing ulcers of the skin- cutaneous diphtheria

12

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

13

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

14

propionibacterium acnes

-sebaceous skin
-lives in hair follicles and eats sebum- oil secreted by skin
-overgrowth can trigger inflammation
-inflammatory acne

15

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

16

Neisseria mucosa

microflora of the oral cavity
aerobic
lives on mucous membranes like the tongue

17

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

18

microflora of the gastrointestinal tract

-the stomach
the small intestine
the large intestine

19

Stomach

low pH and proteolytic enzymes make the stomach inhospitable to most microbes
-some bacteria do colonize in the stomach

20

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

21

the small intestine

-area of rapidly changing pH
-as pH becomes more neutral, bacterial numbers increase

22

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

23

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

24

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

25

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

26

changing the microbiota of the large intestine can affect human health:

ex. oral antibiotics
-opportunistic pathogens can take over
-Antibiotic associated colitis

27

antibiotic associated colitis

-clostridium difficile grows
-inflammation of the colon
treatment: further antibiotics, probiotics, Transpoosition

28

microflora of mucosal tissues

upper respiratory tract
lower respiratory tract
genitourinary tract
female reproductive tract

29

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

30

lower respiratory tract

no resident microflore
-mucous, lysozyme, ciliated cells, secretory IgA, phagocytes

31

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

32

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