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Shigella Flashcards

(48 cards)

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1
Q

What is Shigella?

A

A genus of Gram-negative, non-motile, facultative anaerobic rods

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2
Q

How many species are in the Shigella genus?

A

Four species

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3
Q

What is the serogroup and number of serotypes for S. dysenteriae?

A

Serogroup A, 12 serotypes

Most severe disease

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4
Q

What is the serogroup and number of serotypes for S. flexneri?

A

Serogroup B, 14 serotypes

Common in developing regions

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5
Q

What is the serogroup and number of serotypes for S. boydii?

A

Serogroup C, 18 serotypes

Less common

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6
Q

What is the serogroup and number of serotypes for S. sonnei?

A

Serogroup D, 1 serotype

Most common in industrialized countries; milder illness

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7
Q

What is the primary reservoir for Shigella?

A

Humans (and some primates)

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8
Q

What is the mode of transmission for Shigella?

A

Fecal-oral route

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9
Q

What are the ‘Five Fs’ associated with Shigella transmission?

A
  • Food
  • Faeces
  • Fingers
  • Flies
  • Fomites
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10
Q

What are common contaminated foods that can transmit Shigella?

A
  • Chicken
  • Tuna salad
  • Potato salad
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11
Q

What is the incubation period for Shigella infection?

A

24–50 hours

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12
Q

What is the infective dose for Shigella?

A

Very low (<200 organisms)

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13
Q

How is Shigella spread?

A

Easily transmitted, especially in settings with poor sanitation or hygiene

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14
Q

What are the common symptoms of Shigella infection?

A
  • Diarrhea (can be bloody)
  • Abdominal cramps
  • Fever
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15
Q

What type of organism is Shigella in terms of pathogenesis?

A

Invasive organism that penetrates colonic epithelium

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16
Q

What toxin does Shigella produce?

A

Shiga toxin (an AB-type toxin)

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17
Q

What are the effects of Shiga toxin?

A

Causes mucosal ulceration and inflammation → bloody dysentery

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18
Q

What antibiotic shows increasing resistance in S. sonnei and S. flexneri?

A

Ciprofloxacin

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19
Q

What percentage of S. sonnei and S. flexneri are resistant to Azithromycin?

A

27% resistant

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20
Q

What percentage of S. sonnei and S. flexneri are resistant to Ciprofloxacin?

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A

48% resistant

21
Q

What is the primary method for molecular detection of Shigella from stool?

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A

Direct real-time PCR targeting the Ipa gene

Platforms include EntericBio, BD Max, and BioFire GI Panel.

22
Q

What is the selective media used for Shigella culture on Day 2?

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A

XLD (Xylose Lysine Deoxycholate), DCA (Deoxycholate Citrate Agar), Chromogenic agar (ChromGTI)

Each media has specific characteristics to differentiate Shigella from other organisms.

23
Q

What color colonies does Shigella produce on XLD agar?

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A

Red colonies

Shigella does not ferment xylose, resulting in red colonies.

24
Q

How do Shigella colonies appear on DCA agar?

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A

Pale colonies

This indicates H₂S production.

25
What color colonies does Shigella produce on Chromogenic agar?
Teal-colored colonies
26
What biochemical tests are used for Shigella identification?
Indole: Negative, Methyl Red: Positive, Voges-Proskauer: Negative, Citrate: Negative, Urease: Negative, Lysine Decarboxylase: Negative, Motility: Non-motile, Lactose fermentation: Late, if at all ## Footnote This profile helps confirm the presence of Shigella.
27
What tools are used for biochemical identification of Shigella?
API 20E, Vitek GN card
28
What is performed on Day 3 for Shigella diagnosis?
Identification & Serotyping
29
What tests are performed for confirmation of Shigella?
Whole Genome Sequencing (WGS), Antimicrobial Susceptibility Testing (AST), Serological confirmation
30
True or False: Shigella is motile.
False
31
What is the role of the Salmonella-Shigella-Listeria Reference Laboratory?
Confirmation Testing
32
What is the Kauffmann-White Scheme used for?
Classification of Salmonella based on O and H antigens ## Footnote O antigen is part of the LPS on the outer membrane, and H antigen is associated with motility.
33
What are the two phases of phase variation in Salmonella?
* Phase 1: Specific motile phase * Phase 2: Non-motile or antigenically different
34
How many serovars of Salmonella can be serotyped using the Kauffmann-White Scheme?
Over 2,500 serovars
35
Which organism is non-motile: Shigella or Salmonella?
Shigella
36
Does Salmonella produce H₂S?
Positive
37
What is the appearance of Salmonella colonies on XLD agar?
Red with black centers
38
What is the appearance of Shigella colonies on XLD agar?
Red colonies
39
What is the lactose fermentation characteristic of Salmonella?
Non-lactose fermenter (NLF)
40
What toxin is produced by Shigella?
Shiga toxin
41
What is the IMViC profile for Salmonella?
-+-+ (serovar dependent)
42
Fill in the blank: Salmonella is ______ motile.
motile
43
Fill in the blank: Shigella is ______ in terms of motility.
non-motile
44
Selenite Broth
Salmonella - enhances culture yield by reducing growth of faecal coliforms and faecal streptococci
45
Salmonella Selective Media
1. XLD = red with black centres 2. DCA = colourless with black centre 3. Chromagar = teal with black centres 4. Bismith Sulphite Agar = selective for Salmonella Typhi + Paratyphi
46
DCA (deoxychocolate citrate agar) Sel/Dif
Selective  Sodium deoxycholate  Sodium citrate Differential  Lactose  Sodium ferric chloride
47
XLA (Xylose Lysine Deoxychocolate Agar) Sel/Diff
Selective * Sodium deoxycholate Differetial * Xylose * Lysine * H 2S
48
Bismith Sulphite Agar
Selective for Salmonella typhi + parathyphi

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