FSC-342 Quiz #3 Lecture 14 - Shigella

What family does Shigella belong to?

Enterobacteriaceae.

How is Shigella related to other bacteria?

It is genetically almost identical to Escherichia and closely related to Salmonella.

What are the four species (groups) of Shigella?

1. Shigella dysenteriae (Group A) 2. Shigella flexneri (Group B) 3. Shigella boydii (Group C) 4. Shigella sonnei (Group D)

What are the key characteristics of Shigella?

Gram-negative, rod-shaped, non-spore-forming, and non-motile (no flagella).

What is notable about Shigella’s infective dose?

It has a low infectious dose — fewer than 100 CFU can cause illness.

How many Shigella cells can cause illness?

As few as 100 cells of S. dysenteriae, S. flexneri, or S. sonnei.

How much Shigella can symptomatic individuals shed?

Over 10⁷ CFU per gram of feces.

How long can infected people shed Shigella?

For weeks or even months.

Why is Shigella hard to isolate from food?

It is a poor competitor with normal fecal bacteria and difficult to recover when present in low numbers (<10³ CFU/g).

What temperature conditions can Shigella survive?

It can survive freezing at -20°C and lasts longer in frozen or refrigerated foods than at room temperature.

How does pH affect Shigella survival?

It survives for hours at pH 2–3 and for 1–6 days in acidic foods like orange juice, lemon juice, and wine.

At what salt concentration is Shigella growth inhibited?

Between 3.8% and 5.2% NaCl.

What is the natural reservoir for Shigella?

Humans.

What is the main route of Shigella transmission?

Fecal–oral route.

What is the most common cause of Shigella contamination in food?

Poor personal hygiene of infected food handlers.

What is the second most common factor leading to Shigella outbreaks?

Improper storage of contaminated foods.

Where does contamination most often occur?

Between the processing plant and the consumer, not at manufacturing.

What are the three main transmission routes of Shigella?

Person-to-person, foodborne, and waterborne.

What types of foods are commonly linked to Shigella transmission?

Prepared salads (potato, shrimp, chicken, tuna), inadequately cooked foods, or contaminated equipment.

How does waterborne Shigella transmission occur?

Through untreated or poorly chlorinated water, rivers, or swimming pools—especially in summer.

What is one of the most effective control measures against Shigella?

Proper handwashing.

Is Shigella associated with any specific food type?

No, but outbreaks involve foods like potato salad, chicken, tossed salad, and shellfish.

Where have Shigella outbreaks occurred?

Homes, restaurants, camps, picnics, schools, airlines, and military mess halls.

Which Shigella species causes the majority of outbreaks?

Shigella sonnei (>70% of outbreak cases).

Describe the 2014 Arkansas Shigella outbreak.

Fecal contamination in tomatoes and salsa from poor hygiene and handwashing.

Describe the 2011 Norway Basil/Pesto outbreak.

Fresh basil with high fecal contamination levels.

What is the incubation period for shigellosis?

1–7 days, with a median of 3 days.

What are the main symptoms of shigellosis?

Fever, abdominal pain, cramps, and diarrhea that may be watery or bloody.

What is a hallmark symptom of severe shigellosis?

Bloody diarrhea (dysentery).

How long does recovery from shigellosis usually take?

Typically 1–2 weeks; illness is self-limiting.

How does Shigella cause disease?

It invades epithelial cells, spreads from cell to cell, and produces enterotoxins that cause diarrhea.

What toxin does S. dysenteriae produce?

Shiga toxin, a thermolabile toxin that causes severe infection and bloody diarrhea.

Who is at highest risk for shigellosis?

Children under 6, people with HIV or other illnesses, hospital/nursing home patients, and those affected by disasters disrupting sanitation.

What two key traits distinguish shigellosis from other diseases?

Bloody diarrhea and a very low infectious dose.

What are key prevention measures for foodborne Shigella outbreaks?

Ensure symptomatic food handlers do not work and enforce strict hand hygiene.