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E.coli Flashcards

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1
Q

What is the order Enterobacterales primarily composed of?

A

Gram-negative bacilli

Enterobacterales includes a large number of species, over 350 identified.

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2
Q

What type of anaerobes are Enterobacterales?

A

Facultative anaerobes

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3
Q

What do Enterobacterales reduce nitrate to?

A

Nitrite (NO₂⁻)

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4
Q

What is the oxidase status of Enterobacterales?

A

Oxidase-negative

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5
Q

What is the catalase production level in Enterobacterales?

A

Weakly positive

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6
Q

What type of flagella do most motile Enterobacterales species have?

A

Peritrichous flagella

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7
Q

What color do lactose fermenters produce on MacConkey agar?

A

Pink colonies

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8
Q

Name two lactose fermenters in the Enterobacterales order.

A
  • Escherichia coli
  • Klebsiella spp.
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9
Q

What color do non-lactose fermenters produce on MacConkey agar?

A

Yellow or colorless colonies

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10
Q

Name two non-lactose fermenters in the Enterobacterales order.

A
  • Salmonella spp.
  • Shigella spp.
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11
Q

What is the first step in laboratory investigation of faecal samples?

A

Initial Testing

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12
Q

What type of agar is used for selective and differential plating?

A

Selective and differential agars

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13
Q

What molecular testing method is used for EHEC detection?

A

EntericBio real-time PCR

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14
Q

What is the Gram stain result for Enterobacterales?

A

Gram-negative bacilli

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15
Q

What is the oxidase test result for Enterobacterales?

A

Negative

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16
Q

What biochemical test is positive for E. coli?

A

Indole (I)

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17
Q

What is the Voges-Proskauer test result for Enterobacterales?

A

Negative

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18
Q

E. coli is negative for which citrate utilization test?

A

Citrate Utilization (C)

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19
Q

What does E. coli produce that aids in its identification?

A

Lysine decarboxylase

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20
Q

What are the horizontal gene transfer mechanisms in E. coli?

A
  • Plasmids
  • Bacteriophages
  • Pathogenicity islands
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21
Q

What do plasmids in E. coli carry?

A

Genes for toxins, antibiotic resistance

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22
Q

What are pathogenicity islands?

A

Chromosomal regions with virulence genes

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23
Q

What are the primary intestinal pathotypes of pathogenic E. coli?

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A

ETEC, EPEC, EIEC, STEC/EHEC

ETEC: Enterotoxigenic, EPEC: Enteropathogenic, EIEC: Enteroinvasive, STEC/EHEC: Shiga toxin-producing/E. coli O157:H7

24
Q

What is the main feature of Enterotoxigenic E. coli (ETEC)?

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A

Common in children in developing countries and travelers’ diarrhea; toxins increase cAMP/cGMP, leading to watery diarrhea

25
What type of diarrhea is caused by Enteropathogenic E. coli (EPEC)?
Infantile diarrhea in developing regions; non-toxigenic, non-invasive, damages microvilli in small intestine
26
What does Enteroinvasive E. coli (EIEC) cause?
Dysentery-like illness with bloody diarrhea; invades large intestine cells like Shigella
27
What are the potential outcomes of Shiga toxin-producing E. coli (STEC/EHEC)?
Bloody diarrhea, hemorrhagic colitis, Hemolytic Uremic Syndrome (HUS) ## Footnote HUS includes kidney failure, hemolytic anemia, thrombocytopenia
28
What type of infections do Uropathogenic E. coli (UPEC) cause?
Urinary tract infections (UTIs)
29
What is a significant risk associated with neonatal meningitis-associated strains of E. coli?
Can cross the blood-brain barrier in neonates
30
What are the key characteristics of Enteropathogenic E. coli (EPEC)?
Non-toxigenic, non-invasive; adheres to small intestinal epithelium; forms attaching and effacing lesions
31
What mediates the forming of attaching and effacing lesions in EPEC?
Intimin and TIR proteins via type III secretion system
32
What are the symptoms of Enteroinvasive E. coli (EIEC)?
Fever, abdominal cramps
33
What are the virulence factors of Enteroinvasive E. coli (EIEC)?
Invasion plasmid antigen (Ipa) ## Footnote Ipa enables the invasion of the basolateral membrane and lateral spread cell-to-cell
34
How is Enterotoxigenic E. coli (ETEC) primarily transmitted?
Contaminated food, water, or person-to-person
35
What are the virulence factors of Enterotoxigenic E. coli (ETEC)?
* Colonization factor antigen (CFA) * LT (Heat-labile toxin) * ST (Heat-stable toxin)
36
What is the most common serotype of Shiga toxin-producing E. coli?
E. coli O157:H7
37
What are the clinical manifestations of STEC/EHEC?
* Intestinal: Watery or bloody diarrhea, hemorrhagic colitis * Systemic: Hemolytic Uremic Syndrome (HUS), Thrombotic Thrombocytopenic Purpura (TTP)
38
What does Shiga toxin-producing E. coli (STEC) produce?
Shiga toxins (Stx1, Stx2)
39
True or False: Shiga toxin-producing E. coli (STEC) ferments sorbitol.
False
40
What is the culture media used to identify all E. coli?
MacConkey agar ## Footnote MacConkey agar is selective for Gram-negative bacteria and differentiates lactose fermenters from non-fermenters.
41
What does CT-SMAC stand for?
Cefixime-Tellurite Sorbitol MacConkey ## Footnote CT-SMAC is used to identify sorbitol non-fermenters like E. coli O157:H7, which appear colorless.
42
What color do mauve colonies indicate on STEC Chromagar?
STEC presence ## Footnote Mauve colonies suggest the presence of Shiga toxin-producing E. coli.
43
What is the function of EntericBio Real-Time PCR?
Detects Shiga toxin genes directly from stool ## Footnote This method provides results in approximately 3 hours.
44
What type of labs use EntericBio Real-Time PCR?
Category 3 (Cat 3) biosafety labs ## Footnote Cat 3 labs handle pathogens that can cause serious or potentially lethal disease.
45
What are the characteristics of colony testing for E. coli?
* Gram-negative bacilli * Oxidase negative * Weak catalase positive ## Footnote These biochemical characteristics help in the identification of E. coli.
46
What is the result of the Indole test for E. coli?
Positive (yellow → red with Kovac’s reagent) ## Footnote A positive Indole test indicates the presence of tryptophanase enzyme.
47
What does a positive Methyl Red test indicate?
Medium turns red ## Footnote This indicates strong acid production from glucose fermentation.
48
What is the result of the Voges-Proskauer (VP) test for E. coli?
Negative ## Footnote A negative VP test indicates that acetoin is not produced from glucose fermentation.
49
What does a negative Citrate test indicate?
Medium remains green ## Footnote This means that E. coli cannot utilize citrate as its sole carbon source.
50
What is the lactose fermentation result for E. coli on MacConkey agar?
Yes (pink on MacConkey) ## Footnote Lactose fermenters produce acid, turning the indicator pink.
51
What is the result of Sorbitol Fermentation for E. coli O157:H7?
Yes, except O157:H7 ## Footnote E. coli O157:H7 does not ferment sorbitol, appearing colorless on CT-SMAC.
52
What is the result of the Lysine Decarboxylase test for E. coli?
Positive ## Footnote This indicates the ability to decarboxylate lysine, producing alkaline products.
53
What is the function of the VITEK® System?
Automated ID and antimicrobial susceptibility testing (AST) ## Footnote This system uses colorimetric analysis of biochemical reactions.
54
What are the key features of the VITEK® System?
* Tests 64 individual substrates * Provides organism identification * Antibiotic sensitivity * Rapid turnaround (usually within hours) ## Footnote This system is widely used in clinical microbiology laboratories.
55
What does MALDI-TOF MS stand for?
Matrix-Assisted Laser Desorption Ionization Time-of-Flight Mass Spectrometry ## Footnote This technology provides rapid bacterial identification based on the analysis of protein mass spectra.
56
What are the limitations of MALDI-TOF MS?
* E. coli and Shigella cannot be distinguished * Requires confirmation via other tests (e.g., PCR, serotyping) ## Footnote Both organisms share approximately 93% genetic similarity, making them difficult to differentiate.
57
What is the turnaround time for results from MALDI-TOF MS?
Results in minutes ## Footnote This rapid identification is beneficial in clinical settings for timely diagnosis.

Medical Microbiology lectures (23 decks)

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