FSC-342 Quiz #3: Lecture 11 - Staphylococcus Aureus

What is the morphology of S. aureus?

Small Gram-positive cocci

What is the typical colony appearance of S. aureus?

Creamy white to yellow or orange (>90% of colonies)

Is S. aureus catalase positive or negative?

Catalase positive

What type of metabolism does S. aureus have?

Aerobic or facultatively anaerobic

What type of foodborne illness does S. aureus cause?

Intoxication from ingestion of pre-formed, heat-stable enterotoxin

When are the seasonal peaks of S. aureus food poisoning?

July–August and November–December

What is the growth temperature range of S. aureus?

7–45°C (optimum 35°C)

What is the growth pH range of S. aureus?

4.3–9.3 (optimum 7.0–7.5)

What minimum water activity (aw) is required for S. aureus growth?

aw > 0.86

How does S. aureus tolerate salt?

Up to 16% NaCl

What conditions are required for S. aureus to produce enterotoxin?

Temperature >15°C and pH >5.0

What are the optimum conditions for enterotoxin production?

10–45°C, pH 7–8, aw >0.90, NaCl <10%

How does competing microflora affect S. aureus?

Suppresses growth

Are vegetative cells of S. aureus heat resistant?

No, heat-sensitive (D60°C < 3 minutes)

Does S. aureus survive pasteurization?

No

How is antibiotic resistance carried in S. aureus?

On plasmids (e.g., MRSA strains)

What is the primary reservoir of S. aureus in foodborne outbreaks?

Humans

Where are common human carrier sites for S. aureus?

Skin, nasal cavity, throat, pharynx, hair, fingers, feces

What are some environmental sources of S. aureus?

Air, dust, water, sewage

What animal sources are associated with S. aureus foodborne outbreaks?

Dairy cattle, sheep, goats with mastitis (rare)

What are the main causes of S. aureus foodborne outbreaks?

Infected food handlers, time/temperature abuse, food made too far in advance, poor hygiene, contamination after cooking, prolonged warming

Is S. aureus food poisoning an infection or an intoxication?

Intoxication (toxin causes illness, not bacteria)

How many S. aureus cells are needed to produce enough toxin for illness?

10⁶ CFU/g

How long can it take for S. aureus to produce enough toxin in food?

About 4 hours

What type of molecule is staphylococcal enterotoxin?

Protein, 26–28 kDa

Is staphylococcal enterotoxin heat stable?

Yes, survives pasteurization and 30 minutes of boiling

Which enterotoxin is responsible for ~79% of S. aureus food poisoning outbreaks in the U.S.?

SEA

Which enterotoxin is the second most common and associated with eggs and fish?

SEB

Which enterotoxins are associated with cows and sheep and are rare in humans?

SEC1, SEC2, SEC3

Which S. aureus toxin is also known as toxic shock syndrome toxin?

SEF

What is the average onset time of S. aureus food poisoning?

2–4 hours after ingestion

What is the minimum dose of enterotoxin needed to cause symptoms?

1 ng/g food (100–200 ng consumed)

What are the most common symptoms of S. aureus food poisoning?

Vomiting, nausea, abdominal pain

What other symptoms can occur in S. aureus food poisoning?

Headache, low-grade fever, chills, dizziness, weakness

How long does S. aureus food poisoning usually last?

Up to 24 hours

Is S. aureus food poisoning usually fatal?

No, fatalities are very rare

Who is most susceptible to S. aureus food poisoning?

Children and the elderly

What foods are most commonly implicated in S. aureus food poisoning?

Meats, poultry, egg products, salads, bakery items, dairy

Which meat is especially linked with S. aureus outbreaks?

Ham

What salads are commonly implicated in S. aureus food poisoning?

Egg, chicken, tuna, macaroni, potato

What bakery products are commonly implicated in S. aureus food poisoning?

Custard and cream-filled desserts (cream puffs, éclairs)

Since the 1970s, how common are dairy-associated outbreaks of S. aureus in the U.S.?

Less than 5% of dairy outbreaks

What food caused the 2012 military unit outbreak of S. aureus food poisoning?

Perlo (chicken, sausage, rice dish)

What was the mean incubation time in the 2012 military outbreak?

2.1 hours

What was the S. aureus concentration in the Perlo dish during the 2012 outbreak?

7.2 × 10⁶ CFU/g

What toxin was found in the stool of patients from the 2012 outbreak?

Staphylococcal enterotoxin A

Why did reheating not prevent illness in the 2012 outbreak?

Enterotoxin is heat-stable

What likely caused contamination in the 2012 outbreak?

Handling chicken by hand and leaving food warm overnight (temperature abuse)

What are the key prevention measures for S. aureus food poisoning?

Good hygiene, sanitation, hand washing, glove use

Should infected food handlers prepare food?

No

What is the key rule for food temperature to prevent S. aureus?

Keep hot foods hot and cold foods cold