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Microbiology Exam 3 > 34 - Bacterial Infections of the GI Tract II > Flashcards

34 - Bacterial Infections of the GI Tract II Flashcards

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1
Q

There are several different diagnostic methods to test for a gram negative bacteria. What are they?

A
  • MacConkey agar
  • Indole test
  • Hydrogen sulfite (H2S)
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2
Q

What type of test is the MacConkey agar?

A

It is a lactose fermentation test

  • Positive: colonies of RED will form
  • Negative: colonies of WHITE will form
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3
Q

What would give a positive test result on the MacConkey agar test?

A

E coli

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4
Q

What would give a negative test on the MacConkey agar test?

A

Salmonella

Shigella

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5
Q

What type of test is the indole test?

A

A test for indole production

  • Positive: RED color change
  • Negative: NO color change (white)
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6
Q

What would give a positive test result on the indole test?

A

E. Coli

Vibrio spp.

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7
Q

What would give a negative test result on the indole test?

A

Salmonella

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8
Q

What type of test is the hydrogen sulfite (H2S) production test?

A

A test which can use a variety of medias and can test for gram negative bacteria

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9
Q

What will you see in a positive test result?

A

A black precipitate

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10
Q

What does the indole test differentiate between?

A
  • Salmonella = black precipitate (produces H2S)

- Shingella = no precipitate (does NOT produce H2S)

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11
Q

What are the different types of E coli pathogens that we will talk about?

A

ETEC: Enterotoxigenic

EPEC: Enteropathogenic

EHEC: Enterohemorrhagic

EIEC: Enteroinvasive

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12
Q

What part of the intestines do these pathogens affect?

A

The small intestine

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13
Q

What are the characteristics of EPEC?

A

Enteropathogenic E. Coli

  • Non-inflammatory
  • Gram negative
  • Facultative anaerobe
  • Moderately invasive
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14
Q

What disease does EPEC cause?

A

Enteropathogenic E. Coli

  • Watery diarrhea
  • Symptoms are caused by tissue destruction of the microvilli
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15
Q

What is very important to remember about the epidemiology of EPEC?

A

It is a PEDIATRIC disease

Think P in EPEC is for Peds

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16
Q

Describe the pattern of infection in pediatric patients

A
  • Important pathogen in infants (infantile diarrhea) in developing countries
  • Accounts for 5-10% of pediatric diarrhea in developing countries
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17
Q

Describe the pathogenesis of EPEC

A

Adhesins

  • BfpA (bundle forming pilus)
  • Type III secretion system, Tir
  • Tight binding
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18
Q

Does EPEC use toxins?

A

No, watery diarrhea occurs without toxins in this case

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19
Q

What is a quick way to summarize the actions of EPEC?

A

“Attaching and effacing”

It is really good at attaching to the small intestine wall and taking out the microvilli there

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20
Q

How do you diagnose EPEC?

A

Culture

  • RED on MacConkey agar test for lactose fermentation
  • Indole positive, RED

PCR

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21
Q

How do you treat EPEC?

A

Supportive therapy

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22
Q

What are the characteristics of ETEC?

A

Enterotoxigenic E. coli

  • Gram negative
  • Facultative anaerobe
  • Non-invasive
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23
Q

What disease does ETEC typically cause?

A

Traveler’s diarrhea

  • It is associated with travel to developing countries and consumption of contaminated water or ice
  • Watery diarrhea

T in ETEC is for Traveler’s

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24
Q

What is the epidemiology of ETEC?

A
  • It is the leading cause of bacterial diarrhea in children living in developing countries
  • 200 million cases of diarrhea and 380,000 deaths per year worldwide, mostly in children in developing countries
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25
Q

What is the pathogenesis of ETEC?

A
  • Fimbriae (pili)

- Toxins

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26
Q

Describe the fimbriae of ETEC

A
  • Adherence to epithelial cells via fimbriae
  • The active portion activates adenylate cyclase
  • It then converts ATP to cAMP
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27
Q

What toxins are secreted from ETEC?

A
  • LT (heat liable toxin)
  • ST (heat stable toxin)
  • Plasmid encoded toxins
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28
Q

What type of toxin is the LT (heat liable) toxin?

A
  • An AB toxin

- Increases cAMP*

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29
Q

What type of toxin is the ST (heat stable) toxin?

A
  • A non-AB toxin
  • Does NOT enter the cell
  • Increases cGMP*
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30
Q

What other characteristics do we know about the pathogenesis of ETEC?

A
  • Non-invasive
  • Non-inflammatory
  • Does NOT kill cells, just makes them release a lot of water leading to diarrhea
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31
Q

How do you diagnose ETEC?

A
  • Clinical history

- DNA probes to detect LT and ST encoding genes in clinical samples and cultures

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32
Q

Is it common to do a DNA probe to detect ETEC?

A
  • Research labs and reference labs do this

- It is not common in the clinical setting, but it is becoming more common

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33
Q

What is the treatment for ETEC?

A

Supportive therapy

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34
Q

How do we name all the different types of salmonella?

A

There are over 2500 serotypes

Salmonella enterica serovar ______

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35
Q

There is one typhi type and three non typhi types of salmonella that we will focus on. What are the names?

A

Salmonella enterica serovar Typhi
- “S. Typhi”

Non-typhoidal salmonella

  • S. Cholerasius
  • S. Enteritidis
  • S. Typhimurium
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36
Q

What is important to know about S. Typhi?

A

It is an inflammatory bacteria of the small intestine

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37
Q

What are the characteristics of S. Typhi?

A
  • Gram negative
  • Facultative anaerobe
  • Motile rods, flagellated with H antigen
  • Acid tolerant
  • Intracellular pathogen
  • Highly adapted to humans
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38
Q

What is the epidemiology of S. Typhi?

A
  • Humans are the ONLY reservoir
  • There are only 400-500 cases per year in the US
  • 21 million cases per year
  • 200,000 deaths worldwide
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39
Q

What is the mode of transmission?

A
  • Fecal-oral route

- Contaminated food or water from an infected person

40
Q

What is the infectious dose of bacteria for S. Typhi?

A

10^5 to 10^6 bacteria

You have to have a fairly high amount of bacteria in your system in order for it to cause disease

41
Q

What is the incubation period for S. Typhi?

A

Approximately 13 days

42
Q

What are the progression of symptoms in S. Typhi?

A

General

  • Fever with headache
  • Rising fever over 3 days

Sustained bacteremia (untreated)

  • Typhoid fever (prolonged (4 weeks)
  • GI symptoms
43
Q

What GI symptoms will you see with S. Typhi?

A
  • Chronic colonization of the gall bladder
  • Gall bladder can then be a source as well
  • Re-infection of the intestines due to gall bladder colonization
44
Q

Why is S. Typhi dangerous in terms of the fecal-oral route of transmission?

A

S. Typhi is shed in the stool, even when the person is asymptomatic (Typhoid Mary)

45
Q

What is the pathogenesis of S. Typhi?

A

S. Typhi adheres to M-cells and enterocytes

46
Q

What are M cells?

A
  • Immune cells of the GI tract - macrophages

- Also associated with Peyer’s patches in the ileum

47
Q

How does S. Typhi get inside the M cells?

A

S. Typhi has a Type III Secretion System (T3SS) which mediates the uptake of S. Typhi into M cells

48
Q

What will you see during T3SS mediated uptake of S. Typhi into M cells?

A
  • You will see membrane ruffling where the membrane “ruffles” around the bacteria
  • Once the S. Typhi is inside the M cell, it is able to escape from the vacuole
49
Q

Why do we call T3SS a bacterial molecular syringe?

A

Because it directly injects proteins into the host cell

50
Q

How does S. Typhi travel throughout the body?

A
  • Phagocytosis or T3SS mediated uptake into macrophages
  • Macrophages move to lymph nodes and drain there
  • S. Typhi excapes from macrophages
  • Bacteremia
51
Q

What does bacteremia consist of with S. Typhi?

A
  • Fever from septicemia

- Septicemia from LPS (endotoxin)

52
Q

How do you diagnose S. Typhi?

A

Culture of stool and blood samples on selective media

53
Q

How do you treat S. Typhi?

A

Antibiotic therapy based on susceptibility profile

  • Fluoroquinolones
  • Trimethoprim-sulfamethoxazole
  • Broad spectrum cephlosporin
54
Q

How do you prevent S. Typhi

A
  • Avoid sources of infection (bottled water only, no ice, thoroughly cooked food, avoid raw fruits/vegetables)
  • Vaccination for travelers to endemic areas
55
Q

What is the S. Typhi vacination?

A
  • Ty21A capsule by mouth, 4 doses

- VICPS injection, 1 dose

56
Q

There are also non-typhoidal types of salmonella. What are they again?

A
  • S. Cholerasuis
  • S. Enteritidis
  • S. Typhimurium
57
Q

What are the characteristics of the non-typhoidal types of salmonella?

A
  • Gram negative
  • Facultative anaerobe
  • Motile rods flagellated with H antigen
  • Acid tolerant
  • Intracellular pathogens
58
Q

The characteristics of typhoidal and non-typhoidal salmonella are the same… What is the difference between the two?

A

Non-typhoidal types of salmonella are not as adapted for humans

59
Q

Is non-typhoidal salmonella restricted to humans?

A

NO

  • There are numerous animal resivours
  • Animals can be a source of infection
  • Contaminated poultry, eggs, dairy
60
Q

Is non-typhoidal salmonella commonly transferred human-to-human?

A

No, rarely

61
Q

What is the infectious dose of bacteria for non-typhoidal salmonella?

A

Quite a bit… 10^6-10^8

62
Q

How many cases of non-typhoidal salmonella do we see each year in the US?

A
  • 50,000 cases per year in the US
  • It is a disease of industrialized countries
  • There is a higher incidence in young children and the elderly
63
Q

Are both typhoidal and non-typhoidal types of salmonella inflammatory or just one of them?

A

Both types

64
Q

When will you see symtpoms begin after ingestion?

A

6-48 hours

65
Q

What symptoms will you see?

A

Nausea, vomiting, abdominal cramps, watery diarrhea

66
Q

How long will symptoms last?

A

Persistent diarrhea for 3-4 days
- With or without blood in stool

Spontaneous resolution within 7 days

67
Q

What percent of cases will present with a fever?

A

50%

This is problematic for diagnosis… Not always the same symptoms

68
Q

What does it mean that there is a large symptomatic range for nontyphoidal salmonella?

A

It can present as anything from a loose stool to severe dysentery-like diarrhea

The more severe cases are generally rare

69
Q

What is the pathogenesis of nontyphoidal salmonella?

A
  • Initial stages of infection are very similar to S. Typhi pathogenesis
  • After entry into the macrophage, there are two different scenarios: rapid killing or macrophage carriage
70
Q

Describe the scenario of rapid killing

A

Massive inflammatory response that…

  • Confines the infection
  • Causes active fluid secretion (diarrhea)
71
Q

Describe the scenario of carriage in macrophage

A

This occurs in immunocompromised individuals

  • There is a systemic dissemination or bacteremia of the non-typhoidal salmonella
  • You will see focal infections such as arthritis, osteomyelitis and endocarditis
72
Q

How do you diagnose nontyphoidal salmonella?

A

Serology or culture from blood and stool

73
Q

Describe the serology test for nontyphoidal salmonella

A

The serology aims to detect anti-vi antigen antibodies

74
Q

Describe the culture test for nontyphoidal salmonella

A

You can use selective (differential) media for testing

  • It will be non-lactose fermenting, so WHITE on the MacConkey’s test
  • It will produce H2S, so it will be BLACK on the hydrogen sulfite test
75
Q

How do you treat nontyphoidal salmonella?

A

It depends on whether or not it has become a systemic infection

76
Q

How do you treat salmonella gastroenteritis that is NOT systemic?

A

Supportive therapy

  • Electrolyte replacement
  • Antibiotics are NOT recommended
77
Q

Why are antibiotics not recommended for a nonsystemic infection of nontyphoidal salmonella?

A

Because the antibiotics will actually enhance the carrier state… They can grow better when you wipe out the natural flora with a broad spectrum antibiotic

78
Q

How do you treat a systemic infection from nontyphoidal salmonella?

A

Antibiotic therapy depending upon its resistance profile

79
Q

Is there a vaccine available for nontyphoidal salmonella?

A

No

80
Q

What is campylobacter jejuni?

A

Another inflammatory bacteria that can infect the small intestine

81
Q

What are the characteristics of campylobacter jejuni?

A
  • Gram negative

- Rod or curved “sea-gull” shaped

82
Q

Is campylobacter jejuni exclusive to humans?

A

No - there are many animal reservoirs such as turkey and pets

83
Q

Is campylobacter jejuni invasive?

A

Yes - it is invasive in the jejunum, ileum and colon

84
Q

What disease does campylobacter jejuni cause?

A
  • Ulceration and acute enteritis
  • Watery diarrhea
  • Sepsis eventually
85
Q

Is campylobacter jejuni common?

A

Yes it is the most common cause of bacterial diarrhea

86
Q

What is the incubation period for campylobacter jejuni?

A

2-11 days

87
Q

What does sequelae mean?

A

A condition that is the consequence of a previous disease or injury

88
Q

What sequelae can result from campylobacter jejuni?

A

Guillain-Barre syndrome

89
Q

What is Guillain-Barre syndrome (GBS)?

A

Now called “heterogeneous syndrome”

- It is an acute immune-mediated polyneuropathy

90
Q

What does GBS cause?

A

It causes progressive, symmetric muscle weakness accompanied by absent or depressed deep tendon reflexes

91
Q

Are all cases of GBS similar?

A

No, symptoms vary
- Anywhere from difficulty walking to nearly complete paralysis of extremities, facial muscles, respiratory muscles and bulbar muscles

92
Q

What percent of GBS is attributed to a campylobacter infection?

A

30-40%

93
Q

What is the pathogenesis of campylobacter jejuni?

A

Not much is known, but we think it is similar to salmonella

94
Q

How do you diagnose campylobacter jejuni?

A

Culture

  • This is routinely done
  • Use a selective media in a microaerophilic environment
95
Q

What is the treatment for campylobacter jejuni?

A
  • Supportive therapy mostly

- Antibiotic therapy only in invasive disease and dependent upon the susceptibility profile

96
Q

If you do use antibiotics for campylobacter jejuni, what do you use?

A

Macrolides

Microbiology Exam 3 (8 decks)

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