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Medical Microbiology > Lecture 9 > Flashcards

Lecture 9 Flashcards

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USMLE® Step 1 flashcards Biology 101 flashcards
1
Q

What are coliforms?

A

group of gram-negative, facultative anaerobic rod bacteria | ferment lactose to acid and gas

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2
Q

What can we use coliforms for?

A

used to test contamination of water or food due to feces

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3
Q

What is diarrhea?

A

the excessive discharge of fluids from bowel | it is a symptom, not a disease

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4
Q

What are the 2 types of diarrhea?

A

secretory (watery) and dysentery

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5
Q

What is secretory diarrhea?

A

loss of electrolytes and fluids from small intestine

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6
Q

What is dysentery diarrhea?

A

significant local tissue damage or inflammation of GI tract = causes blood in fluids of diarrhea

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7
Q

Where does dysentery diarrhea mostly occur?

A

large intestine

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8
Q

Where does secretory diarrhea mostly occur?

A

small intestine

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9
Q

In a disease where it causes both secretory and dysentery diarrhea, which one usually happens first?

A

secretory first then bloody second

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10
Q

What are the two most common causes of diarrhea? (viral/bacterial) Which is more severe?

A

most common = VIRAL gastroenteritis || 2nd most common = bacterial gastroenteritis = more severe than viral

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11
Q

How do toxic and invasive bacteria differ from each other?

A

invasive bacteria invade tissues of intestine and toxic bacteria don’t invade but produce toxins that target intestine

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12
Q

Which type of diarrhea is more serious?

A

dysentery diarrhea

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13
Q

What is Enterobacteriaceae?

A

group of gram- pathogens that causes infectious diseases having diarrhea as a symptom

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14
Q

What is Vibrionaceae?

A

another family of bacteria that causes diseases with diarrhea as a symptom

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15
Q

Which Enterobacteriaceae causes only secretory diarrhea?

A

enterotoxigenic E. coli (ETEC) ; enteropathogenic E. coli (EPEC) ; enteroaggregative E. coli (EAggEC)

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16
Q

Which Enterobacteriaceae causes only dysentery diarrhea?

A

enteroinvasive E. coli (EIEC) ; enterohemorrhagic E. coli (EHEC) ; Shigella

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17
Q

Which Enterobacteriaceae causes both types of diarrhea?

A

Salmonella Typhimurium and Yersinia enterocolitica

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18
Q

Which Vibrionaceae causes only secretory diarrhea?

A

Vibrio cholerae

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19
Q

Which Vibrionaceae causes both types of diarrhea?

A

Vibrio parahaemolyticus and Campylobacter jejuni

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20
Q

Which E. coli strain is similar to Shigella?

A

enteroinvasive E. coli (EIEC)

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21
Q

What are the main characteristics of enteric bacteria that causes secretory bacteria?

A

gram- rods, infection in small intestine, does NOT invade, produces enterotoxins targeting small intestine; reservoir = animals or environment; no use of antibiotics for treatment

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22
Q

What are the main characteristics of V. cholera?

A

gram- curved rods ; motile with single polar flagella (Class II) ; facultative anaerobes

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23
Q

Which test can we use to distinguish between Vibrionaceae and Enterobacteriaceae? What are their differences in this test?

A

oxidase reaction = Vibrios are positive and Enterobacteriaceae are negative

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24
Q

What class of flagella do motile Enterobacteriaceae have?

A

Class I = petrichous flagella

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25
Q

Where are Vibrio cholera usually found?

A

in aquatic/marine environments associated with algae and marine invertebrates

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26
Q

What disease does Vibrio cholera commonly cause?

A

cholera

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27
Q

What are the serotypes of V. cholera based off algae?

A

the O antigen

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28
Q

What do serotypes refer to?

A

the different reactivity of species with different antibodies

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29
Q

What is the O antigen part of?

A

part of the LPS on outer cell membrane

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30
Q

What are the 2 main strains of the O antigen and which one is more virulent?

A

O1 and O139; O1 = more virulent

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31
Q

What is the O1 antigen divided into?

A

the Classic and El Tor biovar (indicates a difference at the biochemical level)

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32
Q

Is cholera a new or old disease?

A

old

33
Q

What is required of a disease in order to consider it a pandemic?

A

needs to affect at least 2 continents

34
Q

How many cholera pandemics have occurred thus far?

A

7

35
Q

How does one get infected with cholera?

A

one ingests seafood or drinks water contaminated with V. cholera which will get into GI tract to the small intestine

36
Q

What is “rice water stool”?

A

refers to the 2 layers (“water” and “rice”) of stool sample from a patient with secretory diarrhea

37
Q

What is the mortality rate in untreated patients?

A

60%

38
Q

What are the 4-5 virulence factors of V. cholera?

A

flagella, capsule, Tcp, pili, cholera toxin, other unknown factors

39
Q

What type of toxin is the cholera toxin?

A

AB toxin

40
Q

In what strain is the capsule found? Is this strain the more or less virulent one of the two?

A

O139 which is the less virulent strain

41
Q

What role does the dehydration pili play?

A

with the early interactions with the host cell

42
Q

Why is there no antibiotic resistance in V. cholera?

A

because no antibiotics is used for treatment

43
Q

Why is the flagella considered to be a virulence factor?

A

with no flagella, bacterium cannot cause disease and becomes attenuated

44
Q

What does attenuated mean?

A

weakened in force or effect

45
Q

What vaccines are available against V. cholera?

A

still under development but there is one that provides limited protection for a short time

46
Q

Why do we not administer antibiotics to patients with secretory diarrhea caused by V. cholera? (2 reasons)

A

don’t want to kill off normal flora || don’t want to kill V. cholera because could have toxins inside their cells that if lysed = high amounts of it will be released

47
Q

When would one every administer antibiotics against V. cholera?

A

to reduce toxic production and rapidly eliminate the pathogen

48
Q

What is the main treatment against cholera?

A

oral rehydration therapy

49
Q

What is oral rehydration therapy?

A

prevents dehydration by intaking water that contains salts and glucose

50
Q

How can one prevent contamination of food due to V. cholera?

A

freeze food (kills most of bacteria), proper hygiene and good food preparation practices

51
Q

Who first identified E. coli?

A

Theodore Escherich

52
Q

What are the main characteristics of E. coli?

A

Gram– rods; facultative anaerobes, oxidase negative, motile

53
Q

What is the reservoir for E. coli?

A

humans and animals

54
Q

What are the 5 strains of enteric pathogenic E. coli causing intestinal diseases?

A

ETEC, EPEC, EAggEC, EIEC, and EHEC

55
Q

What does ETEC stand for? What does it cause?

A

enterotoxigenic E. coli causes Traveler’s diarrhea

56
Q

What does EPEC stand for? Who does it affect?

A

enteropathogenic E. coli affecting infants (pedia) under 1

57
Q

What does EAggEC stand for? Who does it infect?

A

enteroaggregative E. coli affecting AIDS patients and newborns under 6months

58
Q

What do EAggEC form that make it difficult to treat?

A

biofilms

59
Q

What does EIEC stand for? What is it similar to?

A

enteroinvasive E. coli = similar to Shigella

60
Q

What does EHEC stand for? What parts of the world is it most common for it to cause an infection and why?

A

enterohemorrhagic E. coli || H= hamburgers = ground beef&raquo_space; more common in nations that like to eat ground beef

61
Q

Do all EHEC strains invade? If no, which one doesn’t?

A

no, strains that cause hemorrhagic colitis don’t invade

62
Q

Which Enterobacteriaceae invade?

A

EIEC and usually EHEC

63
Q

What does ETEC contaminate?

A

water and fresh vegetables

64
Q

Why is the disease ETEC causes called “Traveler’s diarrhea”?

A

our immune systems are naturally used to specific species present in the water/food we eat everyday in our home area but different regions/places have different strains of species = immune system not used to them and reacts = causes diarrheal symptoms

65
Q

What are the virulence factors of ETEC?

A

2 heat-labile toxins (LT-I and LT-II), 2 heat-stable toxins and 1 adhesin

66
Q

Which virulence factor is closely if not similar to the cholera toxin? Why?

A

LT-I as ETEC most likely took the gene from V. cholera; they both use the same pathogenic mechanism

67
Q

Which disease is similar to cholera? Which is milder than the other and why?

A

Traveler’s diarrhea is a milder form of cholera because V. cholera may produce more toxins (not yet identified) that ETEC

68
Q

What toxins does EPEC produce?

A

none have yet been identified

69
Q

What are the virulence factors of EPEC?

A

adhesins, Type III secretion system-Tir receptor, some secreted proteins can be potential toxins

70
Q

What does EPEC cause?

A

diarrhea in infants and small children (p=pedia)

71
Q

Which virulence factor plays a key role in infection?

A

Type II secretion system with Tir receptor

72
Q

What is the consequence due to infection of EPEC?

A

microvilli destruction in small intestine leads to inability to absorb food (malabsorption)

73
Q

What does EAggEC cause?

A

persistent diarrhea in people in both developed and developing countries

74
Q

Why is EAggEC called enteroaggregative? How does this explain the infection it causes?

A

bacteria aggregate and form biofilms on epithelium of small intestine = hard to treat due to biofilm = explains why diarrhea is persistent (lasts long time)

75
Q

What toxins does EAggEC produce?

A

hemolysin and enterotoxin

76
Q

What are symptoms of EAggEC-mediated diarrhea?

A

secretory diarrhea with vomiting, low-grade fever, dehydration

77
Q

What is the main form of treatment for all diseases covered for diarrhea?

A

oral rehydration therapy

78
Q

Are there any vaccines available to treat EAggEC-mediated diarrhea?

A

still under development

Medical Microbiology (20 decks)

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