Lecture 5- Staphylococcal Intoxication

Question 1

What are the general characteristics of foodborne intoxication? (5)

Answer 1

1. Toxin is produced by a pathogen while growing in the food
2. The toxin can be heat liable or heat stable
3. Ingestion of a food containing active toxin, not viable cells, is necessary for poisoning
4. Symptoms generally occur quickly, as early as 30 min after ingestion
5. Febrile symptoms are not present

Question 2

Staphylococcus aureus

Answer 2

• Gram positive cocci
• exists as either single cells or grape like clusters
• nonmotile, noncapsular
• non-spore forming, sensitive to heat treatment
• Facultative anaerobes but grow rapidly under aerobic conditions
• grow at low aw, low pH, under high salt and sugar conditions
• can grow under several adverse conditions, but are poor competitors against other organisms, therefore they do very well when adverse environments gives them a competitive advantage

Question 3

Staphylococcus aureus genome

Answer 3

• accessory genome is made of several mobile genetic elements which can be transferred horizontally and vertically
• carry between 1-4 prophage genomes

Question 4

Staphylococcus aureus toxins

Answer 4

• Causes illness through the ingestion of the toxin not the organism
• the most important factor
• all Sa are enterotoxins and exotoxins
• Endotoxin F causes toxic shock syndrome
• all enterotoxins cause gastroenteritis
• very heat stable!

Question 5

Enterotoxin

Answer 5

• a toxin that acts on the gastrointestinal tract
• made throughout most of the exponential growth phase
• may be involved in quorum-sensing in Sa
• production can be inhibited can be inhibited by the presence of glucose

Question 6

Endotoxin

Answer 6

a toxin that is structurally associated with the bacterial cell (LPS)

Question 7

Exotoxin

Answer 7

a toxin that is usually secreted into the extracellular fluid but can be intracellular or injected directly into eukaryotic cells

Question 8

Exfoliative toxins

Answer 8

dermolytic exotoxins produced exclusively by Sa that cause the symptoms of impetigo or scaled skin syndrome

Question 9

Can Sa grow in other animals before humans? If so, where and what can that cause?

Answer 9

Yes, can cause bovine mastitis

• when a cow with mastitis is milked the bacteria can contaminate milk and dairy products
• cow can also contaminate automated milkers, and facilities contaminating other batches of milk
• if they can grow, the toxins may survive pasteurization

Question 10

What temperature does staphyloccocus grow optimally?

Answer 10

37-49C only 3hr required at this temperature for sufficient toxin production

Question 11

What are some contributing factors to food being contaminated from staphyloccocus? (5)

Answer 11

1. inadequate refrigeration
2. preparing foods too far in advance
3. poor personal hygiene
4. inadequate cooking
5. prolonged used of warming plates (buffet style)

Question 12

What food is S. aureus most commonly found in?

Answer 12

ground beef, big game

Question 13

Characteristics of S. aureus infection

Answer 13

• very quick onset (30 min), mean incubation is 4.4 hours, 10 hrs is max time to onset
• self-limiting and recover in 24-48hrs
• most care are not reported
• never febrile
• outbreaks are seasonal
• symptoms include: vomiting, N/D, abdominal pain
• death is very rare
• purified toxin is considered a bioterrorism agent

Question 14

S. aureus infectious dose

Answer 14

> 10^5 cells/g can cause disease

1 ng/g of toxin in food can cause illness

Question 15

Methicillin-Resistant Sa (MRSA)

Answer 15

• strain carries the mecA gene

- causative agent of soft tissue and skin infections, along with necrotizing fasciitis