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Clinical Micro > GI infections (bacterial) > Flashcards

GI infections (bacterial) Flashcards

1
Q

In developing nations, GI infections are major source of __ &__ where in developed nations they are a source of ___

A

morbidity and mortality
- especially children
just morbidity

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2
Q

Outbreaks of GI infections are usually due to what kind of contamination?

A

food and water contamination

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3
Q

in the developing world, how many cases of GI infections are there a year and how many deaths?

A

~ 1 billion cases / year resulting in 4-6 million deaths (12,600 / day)

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4
Q

What bacterial pathogen causing GI infection has a very long incubation period?

A

E-coli 0157

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5
Q

A very short incubation period for GI disease is indicative of..

A

preformed toxin having been ingested

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6
Q

In 1g of stool, there are approximately how many bacteria?

A

10^11

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7
Q

When are stool samples from a patient rejected?

A
  1. If they’ve been in the hospital more than 72 hours

2. If its not actually diarrhea

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8
Q

What are the 4 main types of selective media (plus one bonus one for Vibrio) that are used to culture stool samples?

A

XLD, Campylobacter agar, MacConkey agar, Sorbitol MacConkey agar

On request, TCBS agar for Vibrio

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9
Q

What is the morphology of Campylobacter sp. ?

A

Gram -ve, highly motile, spiral rod

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10
Q

What are the three species of Campylobacter? How can they be differentiated?

A

Campylobacter jejuni, Campylobacter coli, and C. fetus

C. jejuni is positive for a hippurate test

C. fetus is non-thermophilic unlike the other 2
- rarely causes disease

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11
Q

How does campylobacter rank in terms of causes of community acquired diarrheal diseases?

A

it’s by far #1

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12
Q

What conditions do Campylobacter require for growth?

A

Thermophilic (25 to 43º C) - except C. fetus
- allows you to differentiate between it and other bacteria that won’t grow at elevated temps

Microaerophilic

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13
Q

What additions to the agar need to be made to grow Campylobacter?

A

needs to contain blood or charcoal

-also usually has antibiotics

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14
Q

Whats the incubation period and infective dose for Campylobacter?

A

Incubation period: usually 2-4 days

Infective dose 10^3 – 10^4 cells

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15
Q

What are typical symptoms of a campylobacter infection?

A

Fever, myalgia, etc..
Diarrhea (can be bloody)
Abdominal pain

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16
Q

What is the prognosis of a Campylobacter infection?

A

usually self limiting and resolves in about a week

- people are not normally treated for this

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17
Q

What rare disease has Campylobacter been associated with?

A

Guillain-Barre syndrome

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18
Q

How many true species of Salmonella are there? what are they ?

A

just 3 really

S. enterica, S. bongori, S. subterranea

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19
Q

How many serovars of S. enterica are there?

A

about 2000

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20
Q

What is a special virulence adaptation of Salmonella?

A

Motile because of peritrichous flagella (H antigen).

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21
Q

What two serovars of S. enterica are non-motile?

A

S. gallinarum and S. pullorum

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22
Q

What is the Kauffmann-White antigenic scheme?

A

A way to classify Salmonella based on agglutination reactions with specificantisera against Salmonella antigens

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23
Q

What are 3 types of antigens found on Salmonella that are used for Kauffmann-White profiling?

A

O, H and Vi antigen

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24
Q

What is O antigen ?

A

characteristic sequence of repeatingpolysaccharide units in LPS.

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25
Q

What is the H antigen?

A

flagellar antigens (protein) and mayoccur in one of two phase variations.

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26
Q

What is the Vi antigen? where is it found?

A

Capsular polysaccharide found only in the Salmonella typhi serovar

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27
Q

What is the relationship between infective dose and incubation period for Salmonella gastroenteritis?

A

Incubation period is dose dependent - couple of days on average

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28
Q

When do symptoms usually appear for a Salmonella infection?

A

after about 48 to 72 hours

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29
Q

What are some symptoms of Salmonella gastroenteritis?

A 
Nausea and vomiting 
Diarrhea 
Myalgia 
Fever 
Abdominal pain
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30
Q

What is the typical duration for an infection with Salmonella Gastroenteritis?

A

2-7 days

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31
Q

Are people treated for Salmonella?

A

Yes if they are under 6months or over 50 years

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32
Q

Why are certain people treated for Salmonella?

A

Under 6 months: don’t produce enough stomach acid

Over 50: stomach acid isn’t acidic enough

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33
Q

What is Salmonella Enteric Fever? What causes it?

A

Bacteremic illness caused by S. typhi in the blood

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34
Q

What is the incubation for Salmonella Enteric Fever?

A

10-14 days

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35
Q

What is the best specimen to collect to diagnose Salmonella Enteric fever?

A

Bone marrow sample

- can use blood and urine, almost never find it in stool by the time the patient is presenting with symptoms

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36
Q

What are some symptoms of Salmonella Enteric Fever? (6)

A
  1. myalgia and headache
  2. fever
  3. splenomegaly
  4. leukopenia
  5. abdominal pain
  6. Rose spots (macular rash on abdomen)
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37
Q

What are two possible sequelae of SEF?

A

intestinal haemorrhage and perforation

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38
Q

What is the first step in culturing Salmonella?

A

Need to grow up the number of organisms in a pre-enrichment broth
- inhibits the growth of other organisms in the sample

39
Q

What are the 2 types of pre-enrichment broth? How long do you grow it in there for?

A
  1. Selenite
  2. Tetrathionate

No longer than 16 hours

40
Q

What 4 types of selective and differential media can be used to culture Salmonella?

A

XLD, HE, SS agar, Bismuth-sulfite agar

41
Q

What is XLD media? What does it contain? What is it used for?

A

Contains xylose, lysine, sodium desoxycholate, sodium thiosulfate and ferric ammonium citrate

also has an excess of lactose and sucrose

Selective & differential media for the isolation of gram negative enteric pathogens cultivated from clinical specimens

42
Q

What 3 reactions occur on XLD media

A

1) xylose fermentation,
2) lysine decarboxylation
3) hydrogen sulfide production

43
Q

Enterics (with the exception of Shigella) ferment what sugar rapidly?

A

xylose

44
Q

XLD media is used to differentiate what two pathogens from other enteric gram negatives?

A

Salmonella and Shigella

45
Q

How does XLD media work?

A

Initially Salmonella will ferment the xylose and the colonies will turn yellow due to the acid production
- For shigella, the colonies will remain red as it doesn’t ferment xylose

Gradually the Salmonella colonies will revert back to red as xylose is depleted and lysine decarboxylation is maxed out
- this is prevented from happening in other enterics with the addition of excess lactose and sucrose

Salmonella then produces hydrogen sulfide under alkaline conditions which results in the formation of colonies with black centers, whereas, under acidic conditions, this black precipitation is inhibited
- results in black colonies

46
Q

What would a typical enteric look like on XLD media

A

would turn yellow and remain that way

47
Q

What does shigella look like on XLD media?

A

red, no change in colony colour

48
Q

What does Salmonella look like on an XLD plate?

A

goes from yellow back to red and eventually to the formation of black spotted colonies

49
Q

What is the incubation period for E.coli 0157?

A

3-8 days

50
Q

What symptoms are typical of an E. coli 0157 infection?

A

Diarrhea which can range from mild to grossly bloody
- severe cases = hemorrhagic colitis

Severe abdominal cramping

51
Q

What can occur in up to 10% of cases of E.coli 0157 ?

A

hemolytic urea syndrome (HUS)

52
Q

What is HUS? What is the mortality?

A 
anemia / thrombocytopenia / kidney damage
Significant mortality (~1-5%)
53
Q

Who is more susceptible to developing HUS?

A

very young and very old

54
Q

What does E.coli 0157 produce that makes it so virulent?

A

Shiga like toxin

55
Q

What kind of toxin is shiga-like toxin? How does it act?

A

Subunit toxin:
A: acts at ribosomal level, inhibits protein synthesis
B: binds glycolipid receptor in mammalian cells (renal endothelium)

56
Q

What is a reservoir of E.coli 0157 and why?

A

Cows because they lack the receptor for the shiga like toxin

57
Q

Can other non-0157 strains of E. coli also produce shiga like toxin?

A

yeppp

58
Q

What 2 features are used to distinguish the 0157 strains of E. coli from others? What kind of agar is used? What test ?

A

Virtually all 0157 strains DO NOT fermentsorbitol, whereas most non-0157 strains do

0157 strains are also ß-glucuronidase negative

Latex agglutination is used to confirm 0157 strains

Uses Sorbitol-MacConkey agar

59
Q

What are the 4 species of Shigella and their group

A

S. dysenteriae (Group A)
S. flexneri (Group B)
S. boydii (Group C)
S. sonnei (Group D)

60
Q

What is the results of a TSI slant for Shigella?

A

K/A (red /yellow)

61
Q

Except for S. dysenteriae, all Shigella ferment…?

A

mannitol

62
Q

Are Shigella motile?

A

no

63
Q

What is the result of a Urea test for Shigella?

A

Negative

64
Q

What does Shigella cause in humans?

A

Shigellosis or bacillary dysentery.

65
Q

How is Shigella transmitted?

A

Via the fecal oral route or person to person

66
Q

What is the infective dose for Shigella?

A

VERY low, 10-100 organisms only

67
Q

Is Shigella a zoonotic disease?

A

no

68
Q

What is the incubation period like for Shigella

A

Mid range : 2-4 days

69
Q

What are some symptoms of an infection with Shigella? Early and later symptoms

A

Early: fever, cramping, abdominal pain, and watery diarrhea

Later: frequent, scant stools with blood, mucous, and pus (due to invasion of intestinal mucosa).

70
Q

What determines the severity of Shigellosis?

A

the invading pathogen

- S. dysenteriae is the worst

71
Q

What is the basis for the grouping of the Shigella species?

A

O antigen

- the K antigen is heat labile

72
Q

Why is it important to ID a bacteria as either Shigella or E. coli prior to serotyping?

A

Because the O antigens are very similar

73
Q

What is the virulence factor produced by Shigella? Which species?

A

Shiga toxin

Produced by S. dysenteriae
- in smaller amounts by S. flexneri and S. sonnei.

74
Q

Which bacteria mimics appendicitis ?

A

Yersinia enterocolitica

75
Q

What is a major source of pathogenic strains of Yersinia enterocolitica?

A

Swine

76
Q

What kinds of agar can be used to culture Y. enterocolitia?

A 
CIN agar (Cefsulodin-Irgasan-Novobiocin)
We use MacConkey agar
77
Q

What makes Y. enterocolitica so virulent?

A

the extent to which it can invade host tissue

78
Q

In what ways are Vibrio and Aeromonas similar to Enterobacteriaceae? (5)

A
  1. Gram-negative
  2. Facultative anaerobes
  3. Fermentative bacilli
  4. Cause gastrointestinal disease
  5. found primarily in water sources
79
Q

In what two ways are vibrio and aeromonas different from the enterobacteriaceae ?

A
  1. Oxidase positive

2. Have polar flagella

80
Q

What is the shape of Vibrio?

A

Comma shaped bacilli

81
Q

What are the 3 species of Vibrio that are clinically significant to humans?

A

V. cholerae, V. parahaemolyticus, V. vulnificus

82
Q

What is the range of temperatures across which Vibrio sp. will grow? What about the pH ?

A

Both temp and pH ranges are very broad

18-37ºC
pH 7.0 - 9.0 (useful for enrichment)

83
Q

What two media types (among other simple media) will Vibrio grow on?

A

MacConkey agar

TCBS (Thiosulfate Citrate Bile salts Sucrose) agar

84
Q

What is special about the growth conditions of V. cholera that can be used to distinguish it from other species of Vibrio?

A

It can grow without salt while other strains are halophilic

85
Q

How many serogroups are there for V. cholera? How are they classified?

A

> 200 based on the O antigen

86
Q

Which two serotypes of V. cholera are responsible for epidemic cholera?

A

01 and 0139

87
Q

the 01 serotype of V. cholera can be subdivided into how many biotypes? what are they called?

A

two, called El Tor and classical

88
Q

What is special about certain members of the 01 serotype of V. cholera?

A

Some don’t produce cholera enterotoxin (atypical or nontoxigenic O1 V. cholerae)

89
Q

What is 0129?

A

a vibriostatic agent

90
Q

What is the incubation period for V. cholera like?

A

mid range: 2-4 days

91
Q

What is the infectious dose like for V. cholera? What can affect this?

A

High infectious dose: >10^8 CFU

10^3 -10^5 CFU with achlorhydria or hypochlorhydria(lack of or reduced stomach acid)

92
Q

What are the symptoms of a V. cholera infection?

A

Abrupt onset of vomiting and life threatening watery diarrhea (15-20 L a day of fluid loss)

93
Q

What changes symptom wise as the cholera infection persists?

A 
As more fluid is lost stool changes to rice-water stools:
Colorless
Odorless
No protein
Speckled with mucus

Clinical Micro (28 decks)

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