Causative Agents of Foodborne Diseases: Shigella, Salmonella, and Yersinia

Flashcards in a Question-and-Answer format covering the key concepts about Shigella, Salmonella, and Yersinia as described in the lecture notes.

What are the three key bacterial agents of foodborne diseases discussed in the lecture?

Shigella, Salmonella, and Yersinia.

What shared characteristics do Shigella, Salmonella, and Yersinia have?

They are Gram-negative, facultative anaerobic rods from the Enterobacteriaceae family.

List the Shigella species mentioned.

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

What are two microbiology features of Shigella regarding motility and lactose fermentation?

Non-motile; does not ferment lactose.

What is Shigella's infectious dose?

Approximately 10 cells (low infectious dose).

How does Shigella cause disease in the colon?

It invades colonic epithelial cells, causing cell death and ulceration.

What toxin does Shigella produce and what is its effect?

Shiga toxin; inhibits protein synthesis leading to bloody diarrhea (dysentery).

How is Shigella transmitted?

Through contaminated food or drink.

Through which cells does Shigella enter the colon?

M cells.

What are common symptoms of Shigella infection?

Bloody diarrhea, cramps, inflammation.

What is the treatment for Shigella infection?

Fluid replacement; antibiotics only for severe cases after allergy testing.

What is Hemolytic Uremic Syndrome (HUS) in the context of Shigella?

A rare, serious complication caused by Shiga toxin entering the bloodstream.

What are HUS symptoms and key features?

Hemolytic anemia, thrombocytopenia, acute kidney failure; pallor, decreased urination, swelling, high blood pressure.

Salmonella species include which major ones?

S. enterica (including S. Typhi, S. Enteritidis).

Is Salmonella motile and what toxin does it produce?

Yes, motile; produces H2S.

Where does Salmonella enter and how does it spread?

Enters via M cells in the intestine and can spread systemically, especially typhoidal strains.

Difference between non-typhoidal and typhoidal Salmonella infections?

Non-typhoidal: diarrhea and cramps; Typhoidal: enteric fever with potential complications like intestinal perforation.

Common sources of Salmonella infection?

Undercooked chicken, eggs, unpasteurized foods, contaminated produce (bacteria may originate from animal intestines contaminating eggs).

What are typical symptoms of Salmonella infection?

Diarrhea, nausea, fever; severe cases may involve bacteremia.

Which arteries are rarely affected by Salmonella infections?

Arteries such as the aorta (rare).

Yersinia species are highlighted in the notes.

Y. enterocolitica and Y. pseudotuberculosis.

What growth condition is notable for Yersinia?

Cold-tolerant; grows in refrigerated food.

Where does Yersinia infection typically occur and what condition can it mimic?

Infects the terminal ileum and lymph nodes; mimics appendicitis.

Name two virulence factors of Yersinia.

Invasin and Yersinia outer proteins (Yops).

What disease does Yersinia cause and what are its typical symptoms?

Yersiniosis; fever, abdominal pain, diarrhea (sometimes bloody).

How is Y. enterocolitica transmitted?

Contaminated food, especially unpasteurized meat or milk.

How does Y. enterocolitica enter the gut and where does it spread?

Enters via M cells and spreads to lymph nodes.

What immune evasion strategy does Y. enterocolitica use?

Uses proteins to attach and evade the immune system.

What symptoms can Y. enterocolitica cause?

Appendicitis-like symptoms; reactive arthritis in some people.

What is the virulence combination for Shigella (invasion plus toxin)?

Invades colon cells and produces Shiga toxin, causing bloody diarrhea.

What is Salmonella’s virulence strategy within the host?

Enters the gut, survives in immune cells, and causes inflammation.

How can Yersinia mimic appendicitis and what enhances this resemblance?

Infection of terminal ileum/lymph nodes causing appendicitis-like symptoms.

What laboratory diagnostic methods are used beyond culture for these organisms?

PCR, serotyping, ELISA for toxin detection (Shiga toxin); culture on selective media with specific agar: XLD for Shigella, Hektoen enteric agar for Salmonella, CIN agar with cold enrichment for Yersinia.

What are general prevention and treatment strategies for these infections?

Hygiene and sanitation; food safety (cook meat, pasteurize milk, avoid cross-contamination); antibiotics only for severe/systemic cases due to resistance risk; vaccines available only for S. Typhi (travelers).

Is there a vaccine for any of these pathogens?

Vaccines are available only for S. Typhi (for travelers).