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Enterobacteriaceae Flashcards

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1
Q

What are enterobacteriaceae?

A

A large group of gram negative bacillus that are uniquitous in soil, water, vegetation, and other natural environments

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2
Q

What do enterobacteriaceae form?

A

A significant part of the natural intestinal microbiota in humans

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3
Q

What are the major pathogenic genera of the enterobacteriaceae?

A
  • Escherichia (mainly Escherichia Coli)
  • Salmonella
  • Shigella
  • Klebsiella
  • Proteus
  • Yersinia
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4
Q

What does Yersinia Pestis cause?

A

The plague

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5
Q

What are the major sites of infection from the enterobacteriaceae?

A
  • The GI tract
  • Urinary tract
  • Septicaemias
  • Soft tissue infections
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6
Q

Where do enterobactericeae sometimes infect?

A
  • The genital tract
  • Lower respiratory tract
  • Meninges
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7
Q

What kind of organisms are enterobacteriae?

A

Rapidly growing, facultative anaerobes

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8
Q

What is the result of enterobacteriaceae being faculative anaerobes?

A

They require very little oxygen and produce large numbers in a very short space of time

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9
Q

How can enterobacteriaceae be grown in the labaratory?

A

They can be cultivated on sterine sites, or on more selective media

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10
Q

Give an example of a sterile site that enterobacteriaceae can be grown on?

A

Horse-blood agar

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11
Q

Give an example of a more selective media that enterobacteriaceae can be grown on

A

MacConkey agar

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12
Q

What features allow enterobacteriaceae to be identified microbiologically?

A

They are oxidase-negative, and can convert nitrates to nitrites

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13
Q

How can enterobacteriaceae be differentiated between themselves?

A

E. Coli and some other bacillus can ferment lactose, whereas shigella and salmonella cannot

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14
Q

Why does care need to be taken when testing enterobacteriaceae?

A

They can rapidly multiply and are highly infectious

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15
Q

On what basis can enterobacteriaceae be classified?

A

Serologically, based on the three main groups of antigen

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16
Q

What are the groups of enterobacteriaceae?

A
  • K antigens
  • O antigens
  • H antigens
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17
Q

What do K antigen enterobacteriaceae have?

A

Capsular polysaccharide

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18
Q

What do O antigen enterobacteriaceae have?

A

Polysaccharide polymer on outermost portion of the LPS

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19
Q

What do H antigen enterobacteriaceae have?

A

Flagella proteins

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20
Q

What is the result of the serological classification of enterobacteriaceae?

A

Certain serotypes of the pathogens can be identified by these antigens

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21
Q

Give an example of a serotype of an enterobacteriaceae

A

E. Coli O157:H7

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22
Q

What does E. Coli O157:H7 cause?

A

Haemolytic uraemia

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23
Q

What is haemolytic uraemia?

A

Diarrhoea with potential for causing renal failure

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24
Q

What virulence factors do enterobacteriaceae possess that result in their relatively high ability to cause disease?

A
  • Endotoxins are found abundantly in the outer membrane of the bacillus
  • Polysaccharide capsule
  • Flagella
  • Exotoxins are released
  • Antigenic variation
  • Molecular protein syringes
  • Antimicrobial resistance is acquired regularly from bacteria
  • Sequestration of iron
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25
What does the abundance of endotoxins found on the outer membrane of the enterobacteriaceae allow for?
The development of SIRS and septic shock
26
When are the results of endotoxins in the enterobacteriaceae outer membrane particularly significant?
Following antibiotic mediated cell lysis
27
What is the virulence advantage of the polysaccharide capsule of the enterobacteriaceae?
It enhances ability to evade phagocytic response
28
What is the purpose of the enterobacteriaceaes flagella?
Locomotion
29
What mechanism of action is used by the exotoxins released by enterobacteriaceae?
Similar to the A-B toxin structure to cholera-like toxins
30
What is the virulence advantage of the antigenic variation of enterobacteriaceae?
Regulation of the K and H antigens regularly protect the bacteria from any adaptive immune response
31
What is the virulence advantage of molecular protein syringes in enterobacteriaceae?
They allow the injection of bacteria into the host cell, disrupting the host cell metabolism and protein-protein interactions
32
What is the result of the regular acquisition of antimicrobial resistance by enterobacteriaceae?
Constant antibiotic resistance
33
What do enterobacteriaceae have a remarkable capacity to do?
Exchange genetic information with related and unrelated bacteria
34
What is the virulence advantage of sequestration of iron?
Results in a high affinity for scavenging iron for nutrients
35
What does Escherichia Coli cause?
* 57-77% of UTIs * Blood stream infections * Neonatal meningitis * *In less developed countries*, it causes acute and chronic diarrhoea
36
Are the diseases caused by E. Coli endogenous or exogenous?
All endogenous, apart from intestinal infections
37
What are UTIs mainly caused by?
Contamination of the urethra with endogenous microbiota from the colon
38
What organisms cause UTIs?
Mainly E. Coli, *but other organisms can also cause UTIs*
39
How can UTIs be diagnosed?
* Symptoms * Rrine dipstick of midstream sample * Dipstick for nitrites * Leucocyte esterase * Pure culture of \>10^5 organisms
40
Why is E. Coli particularly effective at causing UTIs?
Because of fimbrial attachments capable of binding to urothelium
41
How can blood stream infections occur?
From E. Coli secondary to a UTI, or from a GI source
42
What may the GI source of a blood stream infection be?
* Intestinal perforation * Intra-abdominal abscess * Inflammation of the colon * GI stasis * Neutropenia
43
Why can neutropenia result in a blood stream infection?
Due to increased seeding of the blood with the GIT microbiota
44
What is neonatal meningitis caused by?
Mainly E. Coli or group B steptococci, *yet there are other pathogens*
45
What group B streptococci causes neonatal meningitis?
S. Agalactiae
46
What does any sign of sepsis in a neonate require?
Testing of the CSF to distinguish between the possible causes
47
How are the possible causes of sepsis in a neonate distinguished?
* Cell count on culture * Gram staining * Glucose assays * Nitrite testing
48
What can cause intestinal infection or infective diarrhoea?
A diverse group of Escherichia Coli serotypes
49
Are the E. Coli that cause intestinal infection or infective diarrhoea endogenous or exogenous?
Exogenous
50
Where is the E. Coli that causes intestinal infection or infective diarrhoea acquired from?
Primarily, from faecally contaminated food, or transmission from person to person
51
What is the main type of E. Coli causing intestinal infection or infective diarrhoea that is transmitted from person to person?
EIEC or shigella
52
What serotypes of E. Coli cause intestinal infection or infective diarrhoea?
* Enterotoxinogenic E. Coli (ETEC) * Enteroaggregative E. Coli (EAggEC) * Enteropathogenic E. Coli (EPEC) * Enteroinvasive E. Coli (EIEC) * Enterohaemorrhagic E. Coli (EHEC)
53
What is ETEC a major cause of?
Travellers' diarrhoea in developing countries
54
What is Travellers' diarrhoea caused by?
Heat stable or labile toxins produced from ETEC
55
What does ETEC infection result in?
Severe, cholera-like watery diarrhoea
56
Is there inflammation in ETEC infection?
No
57
What is the usual outcome of ETEC?
It is usually self limiting
58
What does EAggEC cause?
Persistant, watery diarrhoea in children, which can result in growth retardation and malnutrition
59
Do EAggEC invade cells?
No
60
What is the mechanism of action of EAggEC?
They stack on the mucosa, mediated by their fimbriae, which form biofilms on the membrane
61
What are the pathological features of EAggEC infection?
Inflammation of colon, along with affected absorption and blunted microvilli
62
Where is EPEC seen?
Infants
63
Where are there commonly EPEC outbreaks?
Nurseries
64
What is the mechanism of action of EPEC?
Two-stage docking process; Initially, a loose contant is made with the epithelium and then the bacteria injects a translocated intimin receptor (TIR) which is inserted into the epithelial cell membrane; this TIR then binds to the bacterial adhesions to allow for a tight bound between the bacteria and host cell
65
What is the result of EPEC infection?
Disruption to the microvilli and resultant and malabsorption diarrhoea
66
What is the prevalance of EIEC?
Uncommon
67
What is the action of EIEC similar to?
Shigella
68
What is the mechanism of action of EIEC?
Uses molecular syringes to inject effector molecules into target host cells and escape the phagolysosome and then move via actin-based propulsion
69
How do patients with EIEC infection present?
Watery diarrhoea, with blood, mucus, and leucocytes all found in the stool
70
Why is blood, mucus, and leucocytes found in the stool in EIEC infection?
From the ulceration and acute inflammation
71
How does EIEC spread?
From person to person
72
What has EHEC evolved from?
EPEC
73
What serotype of EHEC are most of the illnesses it causes from?
O157:H7
74
Where does EHEC O157:H7 commonly come from?
Poorly cooked beef
75
What can EHEC infection result in?
Haemmorrhagic colitis or haemolytic uraemic syndrome
76
What is commonly used to identify E. Coli strains?
MacConkey agar
77
Why is MacConkey agar commonly used to identify E. Coli strains?
Because E. Coli strains are comonly very hard to detect on normal media
78
How can molecular testing be used to identify E. Coli?
Can be used to test for genes coding for virulence factors
79
Draw a diagram illustrating the mechanism of action of ETEC
80
Draw a diagram illustrating the mechanism of action of EAEC
81
Draw a diagram illustrating the mechanism of action of EPEC
82
Draw a diagram illustrating the mechanism of action of EIEC
83
Draw a diagram illustrating the mechanism of action of EHEC

Z Old Infection IGNORE (23 decks)

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