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Enterobacteriaceae Flashcards

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
Q

What does the abundance of endotoxins found on the outer membrane of the enterobacteriaceae allow for?

A

The development of SIRS and septic shock

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26
Q

When are the results of endotoxins in the enterobacteriaceae outer membrane particularly significant?

A

Following antibiotic mediated cell lysis

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27
Q

What is the virulence advantage of the polysaccharide capsule of the enterobacteriaceae?

A

It enhances ability to evade phagocytic response

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28
Q

What is the purpose of the enterobacteriaceaes flagella?

A

Locomotion

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29
Q

What mechanism of action is used by the exotoxins released by enterobacteriaceae?

A

Similar to the A-B toxin structure to cholera-like toxins

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30
Q

What is the virulence advantage of the antigenic variation of enterobacteriaceae?

A

Regulation of the K and H antigens regularly protect the bacteria from any adaptive immune response

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31
Q

What is the virulence advantage of molecular protein syringes in enterobacteriaceae?

A

They allow the injection of bacteria into the host cell, disrupting the host cell metabolism and protein-protein interactions

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32
Q

What is the result of the regular acquisition of antimicrobial resistance by enterobacteriaceae?

A

Constant antibiotic resistance

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33
Q

What do enterobacteriaceae have a remarkable capacity to do?

A

Exchange genetic information with related and unrelated bacteria

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34
Q

What is the virulence advantage of sequestration of iron?

A

Results in a high affinity for scavenging iron for nutrients

35
Q

What does Escherichia Coli cause?

A
  • 57-77% of UTIs
  • Blood stream infections
  • Neonatal meningitis
  • In less developed countries, it causes acute and chronic diarrhoea
36
Q

Are the diseases caused by E. Coli endogenous or exogenous?

A

All endogenous, apart from intestinal infections

37
Q

What are UTIs mainly caused by?

A

Contamination of the urethra with endogenous microbiota from the colon

38
Q

What organisms cause UTIs?

A

Mainly E. Coli, but other organisms can also cause UTIs

39
Q

How can UTIs be diagnosed?

A
  • Symptoms
  • Rrine dipstick of midstream sample
  • Dipstick for nitrites
  • Leucocyte esterase
  • Pure culture of >10^5 organisms
40
Q

Why is E. Coli particularly effective at causing UTIs?

A

Because of fimbrial attachments capable of binding to urothelium

41
Q

How can blood stream infections occur?

A

From E. Coli secondary to a UTI, or from a GI source

42
Q

What may the GI source of a blood stream infection be?

A
  • Intestinal perforation
  • Intra-abdominal abscess
  • Inflammation of the colon
  • GI stasis
  • Neutropenia
43
Q

Why can neutropenia result in a blood stream infection?

A

Due to increased seeding of the blood with the GIT microbiota

44
Q

What is neonatal meningitis caused by?

A

Mainly E. Coli or group B steptococci, yet there are other pathogens

45
Q

What group B streptococci causes neonatal meningitis?

A

S. Agalactiae

46
Q

What does any sign of sepsis in a neonate require?

A

Testing of the CSF to distinguish between the possible causes

47
Q

How are the possible causes of sepsis in a neonate distinguished?

A
  • Cell count on culture
  • Gram staining
  • Glucose assays
  • Nitrite testing
48
Q

What can cause intestinal infection or infective diarrhoea?

A

A diverse group of Escherichia Coli serotypes

49
Q

Are the E. Coli that cause intestinal infection or infective diarrhoea endogenous or exogenous?

50
Q

Where is the E. Coli that causes intestinal infection or infective diarrhoea acquired from?

A

Primarily, from faecally contaminated food, or transmission from person to person

51
Q

What is the main type of E. Coli causing intestinal infection or infective diarrhoea that is transmitted from person to person?

A

EIEC or shigella

52
Q

What serotypes of E. Coli cause intestinal infection or infective diarrhoea?

A
  • Enterotoxinogenic E. Coli (ETEC)
  • Enteroaggregative E. Coli (EAggEC)
  • Enteropathogenic E. Coli (EPEC)
  • Enteroinvasive E. Coli (EIEC)
  • Enterohaemorrhagic E. Coli (EHEC)
53
Q

What is ETEC a major cause of?

A

Travellers’ diarrhoea in developing countries

54
Q

What is Travellers’ diarrhoea caused by?

A

Heat stable or labile toxins produced from ETEC

55
Q

What does ETEC infection result in?

A

Severe, cholera-like watery diarrhoea

56
Q

Is there inflammation in ETEC infection?

57
Q

What is the usual outcome of ETEC?

A

It is usually self limiting

58
Q

What does EAggEC cause?

A

Persistant, watery diarrhoea in children, which can result in growth retardation and malnutrition

59
Q

Do EAggEC invade cells?

60
Q

What is the mechanism of action of EAggEC?

A

They stack on the mucosa, mediated by their fimbriae, which form biofilms on the membrane

61
Q

What are the pathological features of EAggEC infection?

A

Inflammation of colon, along with affected absorption and blunted microvilli

62
Q

Where is EPEC seen?

63
Q

Where are there commonly EPEC outbreaks?

64
Q

What is the mechanism of action of EPEC?

A

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
Q

What is the result of EPEC infection?

A

Disruption to the microvilli and resultant and malabsorption diarrhoea

66
Q

What is the prevalance of EIEC?

67
Q

What is the action of EIEC similar to?

68
Q

What is the mechanism of action of EIEC?

A

Uses molecular syringes to inject effector molecules into target host cells and escape the phagolysosome and then move via actin-based propulsion

69
Q

How do patients with EIEC infection present?

A

Watery diarrhoea, with blood, mucus, and leucocytes all found in the stool

70
Q

Why is blood, mucus, and leucocytes found in the stool in EIEC infection?

A

From the ulceration and acute inflammation

71
Q

How does EIEC spread?

A

From person to person

72
Q

What has EHEC evolved from?

73
Q

What serotype of EHEC are most of the illnesses it causes from?

74
Q

Where does EHEC O157:H7 commonly come from?

A

Poorly cooked beef

75
Q

What can EHEC infection result in?

A

Haemmorrhagic colitis or haemolytic uraemic syndrome

76
Q

What is commonly used to identify E. Coli strains?

A

MacConkey agar

77
Q

Why is MacConkey agar commonly used to identify E. Coli strains?

A

Because E. Coli strains are comonly very hard to detect on normal media

78
Q

How can molecular testing be used to identify E. Coli?

A

Can be used to test for genes coding for virulence factors

79
Q

Draw a diagram illustrating the mechanism of action of ETEC

80
Q

Draw a diagram illustrating the mechanism of action of EAEC

81
Q

Draw a diagram illustrating the mechanism of action of EPEC

82
Q

Draw a diagram illustrating the mechanism of action of EIEC

83
Q

Draw a diagram illustrating the mechanism of action of EHEC

Z Old Infection IGNORE (23 decks)

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