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Microbiology > Booklet 7: Medical Microbiology > Flashcards

Booklet 7: Medical Microbiology Flashcards

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Biology 101 flashcards
1
Q

Define human microbiome

A

The collection of all the microorganisms living in association with the human body (microflora, microbiota)

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2
Q

Describe the human microbiome

A 
# of human cells in body = 10^13
# of microorganisms in body = 10^14
# of genes in the human genome = 20,000
# of genes in the micro biome = 20,000,000
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3
Q

When does colonization occur?

A

Immediately after birth

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4
Q

T or F: the diversity of bacterial species present is the exact same between each individual

A

False: it varies quite a lot

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5
Q

Where does microbiota live?

A

-every externally exposed area of the body is colonized by bacteria

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6
Q

T or F: internal tissues that have no exposure to the external environment should not have any microbes

A

True

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7
Q

What are examples of externally exposed areas of the body that would have bacteria?

A
  • skin

- mucous membranes

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8
Q

What are examples of internal tissues that should be free of bacteria?

A
  • blood
  • muscles
  • organs
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9
Q

What is the purpose of having bacteria on your body?

A

-produce beneficial products
-inhibit the growth of some pathogens
Ex. - Lactobacillus acidophilus protects the female reproductive tract.

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10
Q

What are the 3 types of microenvironments in which bacteria live?

A
  • dry skin
  • moist skin
  • sebaceous skin
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11
Q

Give an example of dry skin, moist skin, and sebaceous skin

A

Dry - forearms, hands
Moist - armpits, nostrils
Sebaceous - oily skin on nose, on the upper chest and back

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12
Q

Describe the bacteria on dry skin

A
  • high numbers of Betaproteobacteria
  • second highest is Corynebacteria

-Most bacteria that live on dry skin are harmless, but some do cause skin infections such as Corynebacterium diphtheria which can cause non-healing ulcers of the skin

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13
Q

Describe the bacteria on moist skin

A
  • high numbers of corynebacteria and staphylococci
  • most are harmless commensals (staph epidermis)
  • some are important pathogens (staph aureus)
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14
Q

What can staph aureus cause on the skin?

A

boils, abscesses, or wound infections

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15
Q

Describe the bacteria on sebaceous skin

A
  • High numbers of propionibacteria
  • Propionibacteria are anaerobic actinobacteria that produce propionic acid as an end product of fermentation
  • An example is propionibacterium acnes which causes acne on the skin
  • It lives in hair follicles and eats sebum (oil secreted by the skin)
  • Overgrowth of this can cause inflammation
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16
Q

What antimicrobial enzymes are present in the saliva and mouth?

A

Lysozyme
Lactoperoxidase
Neisseria mucosa
Streptococcus mutans

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17
Q

List some points about Streptococcus mutans

A
  • lives in the oral cavity
  • aerotolerant anaerobe
  • produces a sticky slime layer
  • produces lactic acid as an end product of fermentation
  • degrades tooth enamel
  • can lead to inflammation along the gum line (gingivitis)
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18
Q

What is an example of bacteria that lives in the stomach?

A

Helicobacter pylori

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19
Q

List some points about helicobacter pylori

A
  • colonizes surface of membrane
  • protected from the stomach acid by mucous
  • cause of stomach ulcers
  • has virulence factors:
    • endotoxin - kills cells in the membrane
    • exotoxin - triggers inflammation
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20
Q

Can helicobacter pylori be treated with antibiotics? If so, which one?

A

Yes - tetracycline

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21
Q

In the small intestine: As pH becomes more neutral, bacteria numbers ________ ?

A

Increase

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22
Q

Give an example of bacteria in the small intestine.

A

Enterococcus (Gram positive lactic acid bacteria)

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23
Q

List 4 points about Enterococcus

A
  • opportunistic pathogen
  • frequent cause of nosocomial infections
  • develop antibiotic resistance readily
  • spread resistance genes onto other gram positive bacteria (horizontal gene transfer)
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24
Q

What is the difference between vertical and horizontal gene transfer?

A

Vertical - transfer of genes from parental generation to offspring
Horizontal - transfer of genes between two organisms

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25
Q

What are the pH’s in the stomach, small intestine, and large intestine?

A

stomach - low (acidic)
small intestine - an area of rapidly changing pH from acidic to neutral
large intestine - neutral

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26
Q

Why are they so many microbes in the large intestine?

A

Because there is approximately 10^11 cells/g of feces.

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27
Q

What is an example of bacteria that lives in the large intestine?

A

E. coli

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28
Q

List some points about E. coli living in the large intestine

A
  • most strains living in the large intestine are non-pathogenic
  • may stimulate the immune system
  • produce vitamine K
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29
Q

Although E. coli is the most common example of bacteria living in the large intestine, 16S rRNA shows that E.coli probably makes up less than 1% of the bacteria in the large intestine. So what other types of bacteria live in the large intestine?

A

Bacteroids
Clostridium
- they play an important role in digestion
Some people also have methanogens which may play a role in obesity.

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30
Q

What did studies show when normal mice were compared to germ-free mice?

A

Germ free mice had 40% less body fat. When the germ free mice were inoculated with microbes from the healthy mouse intestine, they quickly gained weight.

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31
Q

What was the result when the microbiomes were compared between the normal weight mice and genetically obese mice? And what does this suggest?

A

Obese mice had fewer Bacteroidetes, more Firmicutes, and way more methanogens.

This suggests that methanogens use up H2 which promotes bacterial fermentation which makes nutrients available to the host.

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32
Q

So we know that changing the microbiota of the large intestine can affect human health. What is an example of something that could change the microbiota of the large intestine?

A

Oral antibiotics.

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33
Q

What happens with antibiotic associated colitis? Also describe the treatment possibilities.

A
  • C. difficile grows
  • Inflammation of colon

Treatment

  • further antibiotics
  • probiotics
  • transpoosition (fecal transplant)
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34
Q

What bacteria are present in the upper respiratory tract?

A
  • staphylococci
  • streptococci
  • corynebacteria
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35
Q

Some people have pathogens among their normal microflora. What are examples of this?

A
  • carriers of a disease

- staph aureus

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36
Q

Are there bacteria in the lower respiratory tract?

A

No.

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37
Q

What is present in the lower respiratory tract?

A

Mucous, lysozyme, ciliated cells, secretory IgA, phagocytes

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38
Q

Genitourinary tract is composed of the upper urinary tract (kidneys and bladder) and the urethra. What bacteria are present in these areas?

A

Upper urinary tract - normally free of microorganisms

Urethra - has some gram negative bacteria

39
Q

What can happen when members of the normal microbiota present in the urethra move to the upper urinary tract?

A

They can act as opportunistic pathogens.

E. coli is one of the most common causes of urinary tract infections.

40
Q

What healthy bacteria is present in the female reproductive tract? Explain why it is healthy.

A

Lactobacillus acidophilus - in the vagina produces lactic acid from glycogen. It lowers the pH and prevents growth of microbes.

41
Q

What can happen if normal microbiota is disturbed in the female reproductive tract?
Ex. lactobacilli killed by antibiotics

A

Yeasts can overgrow and cause yeast infections

42
Q

Define: infection

A

Growth of microbes that are not normally present in the host (regardless of whether or not the host is harmed)

43
Q

Define: disease

A

Damage or injury that impairs regular host functions

44
Q

Define: pathogen

A

A microbe that is able to cause disease

45
Q

Define: opportunistic pathogen

Give 2 examples and explain how they are opportunistic.

A

A microbe that causes disease only in the absence of normal host resistance.

Examples:

  • streptococcus pneumoniae - causes pneumonia in immunocompromised patients
  • E. coli - causes urinary tract infections when bacteria from faces are moved into the urethra
46
Q

What does LD50 mean?

A

It is the dose required to kill 50% of the infected population. (lethal dose)

47
Q

What does ID50 mean?

A

It is the does required to infect 50% of the population. (infectious dose)

48
Q

Define: pathogenicity

A

The ability to cause disease

49
Q

Define: virulence

A

-The severity of the disease that is caused. -(Often given as an LD50 value)

50
Q

What is the LD50 dose for streptococcus pneumoniae?

A

LD50 = 50 cells

51
Q

What is the LD50 dose for salmonella enteric

A

LD50 = 5000 cells

52
Q

Define: pathogenesis

A

The process by which a disease develops. (Steps that lead to an infection and tissue damage).

53
Q

Define: virulence factors

A

Genetically encoded traits that contribute to a pathogen’s ability to cause disease.

54
Q

Define: adherence

A

The ability of a pathogen to stick to a surface and begin colonization.

55
Q

What are 2 examples of non-covalent adherence factors?

A
  • capsules

- slime layers

56
Q

Another example of an adherence factor are adhesins. What are adhesins?

A

Specific surface molecules that allow selective adherence to particular cell types.

57
Q

Give at least 1 example of an adhesin.

There are 2 possible answers

A
  • Strains of enterotoxigenic E. coli produce fimbriae and can adhere specifically to the cells in the small intestine.
  • Neisseria gonorrhoea produce fimbriae that allow it to attach to mucosal epithelial cells.
58
Q

T or F: All pathogens can colonize and grow on the surface of tissues

A

False - some pathogens need to invade the tissue

59
Q

Define: Invasiveness

A

The ability of a pathogen to enter into host cells of spread through tissues

60
Q

List 3 virulence factors that promote invasiveness

A
  • Siderophores
  • Exoenzymes
  • Invasins
61
Q

What are siderophores?

A
  • Iron binding molecules
  • Host proteins transferrin and lactoferrin sequester iron, making it unavailable for microorganisms (limits the growth of the invaders)
  • Siderophores rip iron out of the tissues to be used by bacteria
62
Q

What are exoenzymes?

A

-Excreted by bacteria to degrade host tissues

63
Q

What are the 5 types of exoenzymes?

A
  • Hyaluronidase
  • Collagenase
  • Proteases, nucleases, and lipases
  • Fibrinolysin
  • Coagulase
64
Q

What does hyaluronidase do?

A

It hydrolyzes hyaluronic acid (cement that holds animal cells together). It allows the pathogen to spread between cells

65
Q

What does collagenase do?

A

Degrades collagen (structural component of connective tissue). It allows the pathogen to spread between cells.

66
Q

What do proteases, nucleases, and lipases do?

A

Degrade host macromolecules

67
Q

What does fibrinolysin do?

A

Dissolves fibrin clots.

Ex. Streptococcus progenies makes streptokinase

68
Q

What does coagulase do?

A

Induces fibrin clots.

Ex. Staph aureus produces coagulase to protect it from phagocytes. (Keeps staph infections localized).

69
Q

What are invasins?

A

Proteins that allow bacteria to invade and enter directly into host cells.

70
Q

What is an example of an invasin?

A

Listeria monocytogenes.

-Non-lactic acid, non-spore forming psychrotolerant member of the Firmicutes.

71
Q

Where can Listeria monocytogenes be found?

A

In unpasteurized dairy products, improperly packaged processed meats.

72
Q

What does Listeria monocytogenes do to the body?

A
  • It produces invasions that promote phagocytosis by macrophages.
  • It hijacks the cytoskeleton to escape the phagolysosome.
  • It spreads from cell to cell avoiding a normal humoral immune response.
73
Q

T or F: all pathogens remain localized at the site of the infection

A

False - some have the capability to spread

74
Q

Define: bacteremia

A

Bacteria in the blood (Can be carried to different organs and tissues)

75
Q

Define: septicemia

A

Bacteria multiplying in the blood (A blood borne systemic infection)

76
Q

What can septicemia lead to?

A
  • Sepsis (widespread systemic inflammation)

- Septic Shock (can be caused by gram negative bacteria or gram positives such as staphylococci or enterococci)

77
Q

What are exotoxins and what do they do?

A
  • They are proteins released by growing bacteria.
  • They inhibit host cell function or simply kill the host cells.
  • They can be extremely toxic
  • Usually heat labile.
78
Q

What is an example of an exotoxin?

A

Bacillus anthracis

79
Q

What are the 3 categories of exotoxins?

A
  • Cytoxins
  • AB toxins
  • Superantigens
80
Q

What do cytotoxins do?

A
  • They disrupt cytoplasmic membrane integrity.

- Cell lysis and death.

81
Q

What are the 3 types of cytotoxins?

A
  • Hemolysins
  • Lecithinase or Phospholipase
  • Leukocidins
82
Q

What do hemolysins do and what is an example?

A

They lyse many cells (not just red blood cells).
Ex. Streptococcus pyogenes
- Produces streptolysin which attacks sterols in the membrane

83
Q

What do lecithinase of phospholipase do? What is an example?

A

They dissolve membrane lipids.
Ex. Clostridium perfringens
-alpha toxin (gas gangrene)

84
Q

What do leukocidins do? Example?

A

They destroy white blood cells.
Ex. Staph aureus (staphylococcal alpha toxin)
- Toxin subunits insert into the membrane and oligomerize to form a heptamer

85
Q

What is a heptamer?

A

A membrane spanning pore made of 7 pieces. Cell contents leak out through the heptameter and the cell dies.

86
Q

Describe AB toxins and give an example.

A
  • Two subunits: Active subunit and Binding subunit
  • Ex. diphtheria toxin (interferes with protein synthesis)
    • Subunit B specifically binds to a protein on animal cells
    • Subunit A then moves across the membrane
87
Q

Where is the gene for diphtheria toxin?

A

Not encoded on the chromosome, but instead on a virus

88
Q

Give some other examples of AB toxins.

A
  • Tetanus
  • Botulism
  • Cholera toxins
89
Q

What are super antigens? Describe them.

A

-Activate T cells to elicit an extreme immune response
-Bind to MHC molecules and TCRs outside the antigen binding sites
-Bridge the gap and mimics proper antigen presentation
-Huge number of T cells can be activated
-T cells produce cytokines
-Extreme immune response
-Extreme fever, systemic inflammation, shock, death
Ex. Staph aureus’s toxic shock syndrome.

90
Q

What does systemic inflammation cause?

A

Vasodilation - which can induce shock

91
Q

Salmonellosis (a food borne illness) is another example of how endotoxins are produced. Describe how it harms the body.

A
  • Salmonella colonizes the intestine and multiples to a huge number of bacteria
  • As those bacteria die, they release endotoxin
  • Can cause fever, diarrhea, or generalized inflammation
92
Q

Gram negative sepsis is another example of how endotoxins are produced. Describe how it harms the body.

A
  • Gram negative bacteria multiply in the blood
  • Killed by immune system, which releases an endotoxin
  • Causes massive inflammation and leads to septic shock and death
93
Q

What are more harmful: endotoxins or exotoxins

A

Exotoxins

Microbiology (8 decks)

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