Shigella Flashcards

You may prefer our related Brainscape-certified flashcards:
1
Q

Who discovered the first member of the Shigella genus?

A

Kiyoshi Shiga in 1886

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What is the primary mode of transmission of Shigella?

A

Fecal-oral contamination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Which Shigella species produces the Shiga toxin?

A

Shigella dysenteriae serotype 1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What is the minimum infective dose of Shigella?

A

10-100 bacilli

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What are the typical symptoms of Shigellosis?

A

Abdominal pain, tenesmus, dysentery (bloody diarrhea), vomiting

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What are the four species of the genus Shigella?

A

S. dysenteriae, S. flexneri, S. boydii, S. sonnei

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What environmental conditions can help spread Shigella?

A

Inadequate sanitation, overcrowding, and contamination via flies

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

What type of bacteria is Shigella (Gram stain)?

A

Gram-negative short rods

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Which medium is the best selective media for Shigella species?

A

Xylose Lysine Deoxycholate (XLD) agar

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is the primary reservoir of Shigella?

A

Humans

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What are the biochemical characteristics of Shigella species?

A

Oxidase negative, catalase positive (except S. dysenteriae serotype 1)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What temperature range is suitable for Shigella growth?

A

6-48°C, with an optimum of 37°C

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

How is Shigella differentiated from Escherichia coli?

A

Based on pathogenicity, failure to ferment lactose, and serology

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What is the effect of Shiga toxin produced by S. dysenteriae?

A

Inhibits protein synthesis in susceptible mammalian cells

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

Which Shigella species is most often associated with outbreaks in developed countries?

A

Shigella sonnei

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What are the virulence factors of Shigella species?

A

Invasiveness, intracellular survival, production of Shiga toxin

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What type of stool sample should be collected for Shigella diagnosis?

A

Freshly passed stool or mucus flecks

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What is the incubation period for Shigellosis?

A

12 hours to 4 days

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

What are the two stages of Shigellosis?

A

Early stage with watery diarrhea and second stage with dysentery

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

Which laboratory method is used to identify Shigella serogroups?

A

Slide and tube agglutination tests

21
Q

What is the significance of Shigella’s low infective dose?

A

It allows infection with as few as 10-100 bacterial cells

22
Q

What is the clinical presentation of Shigellosis?

A

Fever, abdominal cramps, watery diarrhea, and bloody stool

23
Q

Which serotype of Shigella dysenteriae is known as Shiga’s bacillus?

A

Serotype 1

24
Q

Which species of Shigella can ferment mannitol?

A

S. flexneri and S. boydii

25
Q

Which biochemical test is negative for all Shigella species?

A

Urease test

26
Q

Which culture media are commonly used for Shigella?

A

Nutrient agar, MacConkey agar, XLD agar, SSA (Salmonella-Shigella Agar)

27
Q

What is the treatment of choice for Shigellosis in children?

A

Azithromycin

28
Q

What are the two phases of Shigella sonnei colonies?

A

Phase I and Phase II (larger, flatter colonies)

29
Q

How does Shigella invade the human body?

A

Via the membranous (M) cells in Peyer’s patches

30
Q

What role do flies play in the transmission of Shigella?

A

They can transfer the bacteria from feces to food

31
Q

What is the function of the Shiga-like toxin (SLT)?

A

Inhibits protein synthesis in cells by targeting ribosomes

32
Q

What are the main components of Shigella diagnosis in the laboratory?

A

Macroscopic examination, microscopy, culture, biochemical tests, PCR

33
Q

What are the characteristic biochemical reactions of Shigella on TSI agar?

A

K/A (alkaline slant, acid butt) with no H2S production

34
Q

What does the presence of polymorphonuclear leukocytes in stool indicate?

A

Shigellosis

35
Q

Which part of the gastrointestinal tract does Shigella primarily infect?

A

Large intestine (colon)

36
Q

What is the major virulence factor for tissue invasion by Shigella?

A

Ipa genes on the virulence plasmid

37
Q

Which bacteria can cause bacillary dysentery apart from Shigella?

A

Escherichia coli, Vibrio parahaemolyticus, Campylobacter jejuni

38
Q

What are the two types of toxins produced by Shigella dysenteriae type 1?

A

Exotoxin (Shiga toxin) and Verocytotoxin

39
Q

What kind of stool is typical in cases of bacillary dysentery caused by Shigella?

A

Scanty, unformed stools with blood and mucus

40
Q

What is the preferred antibiotic for treating Shigellosis in adults?

A

Ciprofloxacin

41
Q

Which Shigella species is the only one to be catalase negative?

A

Shigella dysenteriae serotype 1

42
Q

How is Shigellosis primarily transmitted in developed countries?

A

Through uncooked food or contaminated water

43
Q

Which biochemical reaction helps differentiate Shigella sonnei from other species?

A

Positive β-D-galactosidase and ornithine decarboxylase reactions

44
Q

How do flies contribute to the spread of Shigella in areas with poor sanitation?

A

They act as passive vectors between feces and food

45
Q

What sanitation practices help prevent Shigellosis?

A

Sewage disposal, water chlorination, handwashing

46
Q

What is the clinical significance of Shigella sonnei in developed countries?

A

Causes mild dysentery and is associated with foodborne outbreaks

47
Q

How does Shigella dysenteriae cause neurological effects?

A

Via the neurotoxic activity of Shiga toxin

48
Q

What is the diagnostic role of Cary-Blair transport media for Shigella?

A

Preserves the viability of the bacteria during transport to the lab

49
Q

What does a positive methyl red test indicate in Shigella?

A

Presence of acidic fermentation products