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MCIM 224 > 19 Introduction to Host-Microbe Interactions > Flashcards

19 Introduction to Host-Microbe Interactions Flashcards

1
Q

3 ways microbes can interact w/ a human host?

A
  1. Commensalism
  2. Mutualism
  3. Parasitism
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2
Q

Define commensalism:

A

When microbes benefit by being associated w/ a human, but the human is unaffected

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3
Q

Define mutualism:

A

Both the human and the microbes benefit from the interaction

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4
Q

Define parasitism:

A

The microbes benefit, but the human host is HARMED

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5
Q

Which of the following are usually associated w/ the “normal flora” of humans?

a. Commensalism
b. Mutualism
c. Parasitism

A

a and b

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6
Q

Define “normal flora”

A

The total microbial population (mainly bacterial) that is found associated with a healthy human

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7
Q

One human contains ____ human cells and ____ bacterial cells.

A

10^13, 10^14

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8
Q

Where are normal flora usually found?

A

Found at all body sites that are exposed to the external environment

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9
Q

T or F: “External” body sites includes the intestinal tract.

A

T (so we’ll find normal flora there too)

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10
Q

T or F: The normal flora of an individual is static and doesn’t change.

A

F

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11
Q

Where are normal flora NOT usually found?

A

Internal tissues & organs, and the fluids within those organs
(ie. “Sterile” sites)

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12
Q

T or F: The muscles contain normal flora.

A

F

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13
Q

T or F: The heart contains normal flora.

A

F

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14
Q

T or F: The large intestine contains normal flora.

A

T

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15
Q

Define “colonization”

A

When a microbe becomes established and begins to grow on an “external” body surface

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16
Q

Define “infection”

A

When a microbe penetrates a body surface, enters and multiplies within the body tissue (which should be sterile), and usually
triggers the host’s immune response

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17
Q

Define “disease”

A

An infection that results in damage to the body

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18
Q

T or F: You can have an infection w/o a disease.

A

T

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19
Q

T or F: Normal flora are usually restricted to infection and disease, but not colonization

A

F

They’re usually restricted to colonization, but CAN progress to infection and disease.

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20
Q

In terms of length of time normal flora are associated w/ a host, what’re the two types of normal flora?

A
  1. Transient normal flora

2. Resident normal flora

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21
Q

3 properties of transient flora:

A
  • Short-term association with a host (hours → days)
  • Highly variable in types and numbers of species present
  • Greatly influenced by external factors (diet, hygiene, etc.)
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22
Q

3 properties of normal flora:

A
  • Long-term association with a host (months → life)
  • More stable in types and numbers of species present
  • Much less influenced by external factors
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23
Q

T or F: A fetus is exposed to normal flora before it’s even born

A

F

A fetus in the uterus is STERILE

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24
Q

How do newborns get normal flora?

A

At birth, newborns are exposed to normal flora from many soruces

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25
Q

Stable populations may take _____ to _____ to develop and the final species composition is determined by many factors

A

weeks to months

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26
Q

T or F: Normal flora will vary from person to person, but are constant from one body site to another on the same person, and are also static at one body site over time.

A

F

They also vary from one body site to another on the same person.

They ALSO vary on the same body site over time

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27
Q

What determines site to site diffs in normal flora?

A
  1. Types & amounts of nutrients, pH, oxygen concentration, etc.
  2. Presence / absence of anti-microbial substances eg. Lysozyme in tears
  3. Kinds of other microbes present (what are your neighbors like?) [eg. Competition for nutrients, physical space, etc.]
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28
Q

Describe the normal flora on the skin.

A
  1. Less species diversity
  2. Transient pops on exposed surfaces (due to shedding), but resident pops in “protected” areas (e.g. pores)
  3. Mostly commensal (but some mutualistic interactions i.e. both of us benefit)
  4. They MAY cause disease if they get into body via cuts/scrapes
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29
Q

How do skin flora cause probs w/ blood cultures?

A

The skin flora could be introduced (contaminate) into pt’s blood, and show up in blood cultures

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30
Q

How to tell if a microbe that grows in a blood culture is a true pathogen or only a skin contaminant?

A

Collect >1 blood sample from diff sites > a true pathogen causing bacteremia will be present in ALL samples

31
Q

Describe the normal flora of the respiratory tract. (3)

A
  1. Mouth, tongue, teeth, saliva > Gram positive and negative bacteria, often as biofilm communities
  2. Upper resp. tract/Nasal area > similar flora to skin and mouth
  3. Lower resp. tract (from trachea into lungs) > No normal flora
32
Q

Where is Staph. aureus usually found in 10-15% of ppl?

A

Upper respiratory tract (part of their normal flora)

33
Q

What normal flora bacteria metabolizes sugar in the mouth, and causes dental caries?

A

Streptococcus mutans

34
Q

T or F: Urine in the bladder is sterile in healthy ppl

A

T

35
Q

First 1 cm of urethra is…

A

transiently colonized by various species

36
Q

How many bacteria present in urine usually means the presence of a urinary tract infection?

A

> 10^4 bacteria/ml

37
Q

What kinds bacteria usually are found in the stomach?

A

Bacteria that are acid-tolerant

38
Q

Where are bacteria more likely to be found in the small intestine?

A

Posterior end of the sm. intestine

39
Q

Where in the GI tract are the most bacteria found?

A

Colon

40
Q

99% of bacteria in the colon are… (2)

A

anaerobes or facultative anaerobes

41
Q

“Coliforms” are…

A

bacteria found in the colon only (e.g. E. coli and relatives)

42
Q

T or F: The intestinal tract contains the least number of normal flora, and the fewest diversity of species, relative to other body sites

A

F

Compared to other body sites, the intestinal tract:

  • Contains the greatest total number of normal flora
  • Contains the greatest diversity of species
43
Q

Composition of gut flora is greatly influenced by ___.

A

diet

44
Q

The intestinal tract is often the site of ______ microbe-host interactions.

A

mutualistic

45
Q

Lactose is broken down into glucose and galactose via this enzyme.

A

lactase

46
Q

What happens if a person has reduced lactase production, and they ingest lactose?

A

Lactose passes undigested into large colon > lactic acid bacteria break it down > gas and acidic wastes are released as these bacteria grow > cramps, nausea, diarrhea result

47
Q

How can inds deal w/ lower lactase production? (2)

A
  1. Avoid foods w/ lactose

2. Lactase supplements that help to break lactose down before it enters gut

48
Q

How do artificial sweeteners affect glucose tolerance?

A

Artificial sweeteners change the normal flora of the gut > speed up development of glucose intolerance

49
Q

What’s the link b/w intestinal flora and obesity?

A

They differ in terms of their normal intestinal flora

Some studies have looked at transplanting the normal flora of obese rats to lean rats > lean rats become obese

50
Q

Known fns of the normal flora? (2)

A
  1. Key element in human nutrition

2. Defense against infection by pathogens

51
Q

How can intestinal bacterial normal flora add metabolic traits that humans don’t have?

A
  1. Synthesize essential vitamins (B, K)

2. Salvage E and nutrients that otherwise escape digestion

52
Q

How can intestinal bacterial normal flora be harmful?

A
  1. By breaking down natural cmpnds into carcinogens

2. By releasing metabolic wastes that irritate gut mucosal tissues

53
Q

Name two ways normal flora facilitate defense against infections by pathogens.

A
  1. “Priming” (training) the immune sys

2. Excluding pathogens from body sites

54
Q

What is “Fecal Microbiota Transplantation” (FMT) used for?

A

Treating C. difficile colitis

55
Q

What does “Fecal Microbiota Transplantation” (FMT) involve?

A

Restoring intestinal normal flora by introducing feces obtained from healthy donor

56
Q

T or F: Fecal transplants are not intended to kill C. diff

A

T

They are only used to restore normal intestinal flora

57
Q

Why is the best donor someone who is related to you, or lives with you?

A

B/c they share an envir and eat the same foods as you

58
Q

T or F: Fecal transplants are MORE effective than antibiotics at re-establishing intestinal flora and eliminating C. difficile

A

T

59
Q

Three other GI conditions that may be treated by fecal transplantation?

A
  1. Inflammatory bowel diseases
  2. Bacterial enterocolitis
  3. Irritable bowel syndrome
60
Q

Define “opportunistic pathogen”:

A

a microbe which is not pathogenic under normal conditions > causes disease if introduced into a normally sterile body site (or into a host with a compromised immune system)

61
Q

T or F: V. few species of bacteria has the potential to cause disease if presented with the right opportunity

A

F

Almost ANY species can cause disease if given the opportunity to do so

62
Q

How can normal flora be UNINTENTIONALLY be altered/manipulated?

A

Long term antibiotic use > disrupts balance of intestinal flora

63
Q

How can normal flora be INTENTIONALLY be altered/manipulated? (3)

A
  1. Fecal microbiota transplants
  2. Prophylactic antibiotics
  3. Probiotics
64
Q

Define “probiotics”

A

“Live microorganisms which, when administered in adequate

amounts, confer a health benefit to the host”

65
Q

Most common genuses of bacteria found in probiotics?

A
  1. Lactobacillus

2. Bifidobacteria

66
Q

Define PRObiotic:

A

Living bacteria consumed alone, or as part of a food (eg. yogurt)

67
Q

Define PREbiotic:

A

Nutrients (fiber, carbohydrates, etc.) that you consume, but are then used to support the growth by pre-existing beneficial bacteria in the gut > Increased numbers of beneficial bacteria

68
Q

How do probiotics work? (3)

A
  1. “competitive exclusion” of pathogens
  2. stimulate mucus production by intestinal cells > strengthen the intestinal epithelia barrier
  3. suppress inflammation and stimulate antibody production (interaction w/ the human immune sys)
69
Q

T or F: Diff strains of Lacto and Bifido have diff probiotic effects

A

T

70
Q

What is necrotizing enterocolitis (NEC)?

A

A condition (usually found in premature, v. low birthweight infants) where GI tissue is damaged and begins to die off

71
Q

Normal flora are ____ and ____.

A

normal, variable

72
Q

Normal flora are mainly _____ to the human host

A

beneficial

73
Q

Can normal flora cause disease?

A

Yes

MCIM 224 (25 decks)

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