Shigella

Question 1

Who discovered the first member of the Shigella genus?

Answer 1

Kiyoshi Shiga in 1886

Question 2

What is the primary mode of transmission of Shigella?

Answer 2

Fecal-oral contamination

Question 3

Which Shigella species produces the Shiga toxin?

Answer 3

Shigella dysenteriae serotype 1

Question 4

What is the minimum infective dose of Shigella?

Answer 4

10-100 bacilli

Question 5

What are the typical symptoms of Shigellosis?

Answer 5

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

Question 6

What are the four species of the genus Shigella?

Answer 6

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

Question 7

What environmental conditions can help spread Shigella?

Answer 7

Inadequate sanitation, overcrowding, and contamination via flies

Question 8

What type of bacteria is Shigella (Gram stain)?

Answer 8

Gram-negative short rods

Question 9

Which medium is the best selective media for Shigella species?

Answer 9

Xylose Lysine Deoxycholate (XLD) agar

Question 10

What is the primary reservoir of Shigella?

Answer 10

Humans

Question 11

What are the biochemical characteristics of Shigella species?

Answer 11

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

Question 12

What temperature range is suitable for Shigella growth?

Answer 12

6-48°C, with an optimum of 37°C

Question 13

How is Shigella differentiated from Escherichia coli?

Answer 13

Based on pathogenicity, failure to ferment lactose, and serology

Question 14

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

Answer 14

Inhibits protein synthesis in susceptible mammalian cells

Question 15

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

Answer 15

Shigella sonnei

Question 16

What are the virulence factors of Shigella species?

Answer 16

Invasiveness, intracellular survival, production of Shiga toxin

Question 17

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

Answer 17

Freshly passed stool or mucus flecks

Question 18

What is the incubation period for Shigellosis?

Answer 18

12 hours to 4 days

Question 19

What are the two stages of Shigellosis?

Answer 19

Early stage with watery diarrhea and second stage with dysentery

Question 20

Which laboratory method is used to identify Shigella serogroups?

Answer 20

Slide and tube agglutination tests

Question 21

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

Answer 21

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

Question 22

What is the clinical presentation of Shigellosis?

Answer 22

Fever, abdominal cramps, watery diarrhea, and bloody stool

Question 23

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

Answer 23

Serotype 1

Question 24

Which species of Shigella can ferment mannitol?

Answer 24

S. flexneri and S. boydii

Question 25

Which biochemical test is negative for all Shigella species?

Answer 25

Urease test

Question 26

Which culture media are commonly used for Shigella?

Answer 26

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

Question 27

What is the treatment of choice for Shigellosis in children?

Answer 27

Azithromycin

Question 28

What are the two phases of Shigella sonnei colonies?

Answer 28

Phase I and Phase II (larger, flatter colonies)

Question 29

How does Shigella invade the human body?

Answer 29

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

Question 30

What role do flies play in the transmission of Shigella?

Answer 30

They can transfer the bacteria from feces to food

Question 31

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

Answer 31

Inhibits protein synthesis in cells by targeting ribosomes

Question 32

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

Answer 32

Macroscopic examination, microscopy, culture, biochemical tests, PCR

Question 33

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

Answer 33

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

Question 34

What does the presence of polymorphonuclear leukocytes in stool indicate?

Answer 34

Shigellosis

Question 35

Which part of the gastrointestinal tract does Shigella primarily infect?

Answer 35

Large intestine (colon)

Question 36

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

Answer 36

Ipa genes on the virulence plasmid

Question 37

Which bacteria can cause bacillary dysentery apart from Shigella?

Answer 37

Escherichia coli, Vibrio parahaemolyticus, Campylobacter jejuni

Question 38

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

Answer 38

Exotoxin (Shiga toxin) and Verocytotoxin

Question 39

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

Answer 39

Scanty, unformed stools with blood and mucus

Question 40

What is the preferred antibiotic for treating Shigellosis in adults?

Answer 40

Ciprofloxacin

Question 41

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

Answer 41

Shigella dysenteriae serotype 1

Question 42

How is Shigellosis primarily transmitted in developed countries?

Answer 42

Through uncooked food or contaminated water

Question 43

Which biochemical reaction helps differentiate Shigella sonnei from other species?

Answer 43

Positive β-D-galactosidase and ornithine decarboxylase reactions

Question 44

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

Answer 44

They act as passive vectors between feces and food

Question 45

What sanitation practices help prevent Shigellosis?

Answer 45

Sewage disposal, water chlorination, handwashing

Question 46

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

Answer 46

Causes mild dysentery and is associated with foodborne outbreaks

Question 47

How does Shigella dysenteriae cause neurological effects?

Answer 47

Via the neurotoxic activity of Shiga toxin

Question 48

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

Answer 48

Preserves the viability of the bacteria during transport to the lab

Question 49

What does a positive methyl red test indicate in Shigella?

Answer 49

Presence of acidic fermentation products