FSC-342 Quiz #3 Lecture 13 - Salmonella

What is the Gram reaction and shape of Salmonella?

Gram-negative, short rod, non-spore forming, facultatively anaerobic.

To which family does Salmonella belong?

Enterobacteriaceae.

How is Salmonella motile?

By peritrichous flagella; isolates are motile, lactose non-fermenters, and H2S positive.

How many species of Salmonella exist?

Two.

On what is Salmonella serotyping based?

O antigen (lipopolysaccharide) and H antigen (flagellin protein).

What are the three most prevalent serovars of Salmonella?

Enteritidis, Typhimurium, and Newport.

What is the temperature growth range of Salmonella?

2°C to 54°C.

Can Salmonella survive at freezing and room temperatures?

Yes, it can survive for extended periods.

What is the minimum water activity (a_w) needed for Salmonella growth?

Approximately 0.93.

Can Salmonella survive in low water activity foods?

Yes, it survives well.

At what salt concentration is Salmonella inhibited?

3–4% NaCl, but tolerance increases with temperature and varies by strain.

When does Salmonella become more heat resistant?

At low aw, in rich media, and stationary phase.

What happens after sub-lethal heating of Salmonella?

Heat shock proteins are produced.

What pH range allows Salmonella growth?

Approximately 4.0 to 9.5, depending on acidulant.

Which acid is most effective at inhibiting Salmonella?

Acetic acid (then lactic, citric, HCl).

What is the acid tolerance response (ATR) in Salmonella?

Brief exposure to mild acid (pH 5.5–6.0) allows survival at pH 3.0–4.0.

How does ATR affect resistance?

Increases resistance to both heat and salt.

How long after exposure do symptoms of salmonellosis appear?

8 to 72 hours.

What are the main symptoms of salmonellosis?

Non-bloody diarrhea and abdominal pain.

What is the primary treatment for salmonellosis?

Fluid replacement; antibiotics may prolong carrier state.

What is the human infectious dose of Salmonella?

~10–100 cells in susceptible individuals.

What are the main reservoirs of Salmonella?

Farm animals (cattle, poultry, sheep, swine) plus cats, wild birds, and rodents.

Which reservoir is linked to Salmonella Enteritidis?

Poultry and eggs (~1 in 20,000 eggs contaminated).

Which foods are commonly contaminated by S. Typhimurium?

Beef, pork, lamb, fish, and shellfish.

Which foods are at risk from S. Newport and S. Typhimurium?

Fruits and vegetables via irrigation water, fertilizer, and poor hygiene.

Why is peanut butter a risky food for Salmonella survival?

Low aw (0.53) prevents growth but allows long-term survival.