Lecture 2- Staphylococcal Food poisioning

Question 1

When and what symptoms appear due to Staphylococcal food poisonings?

Answer 1

-abrupt and severe onset
-Occurs usually 1-6 hours after eating
-Severe nausea and vomiting, no fever

Question 2

Is it the bacteria that makes you sick?

Answer 2

No, its staphylococcal enterotoxins, a protein exotoxins released during growth of Staphylococcus aureus

Question 3

Who and How does S.aureus contamination occur?

Answer 3

during preparation and processing. Human cause contamination mainly. 30-50% human population are carriers of s.aureus.
Failure in refrigeration process or growth permissive temp during processing

Question 4

What food effected by S.aureus?

Answer 4

• Cream/milk
• Butter
• Ham
• Cheeses
• Sausages
• Salads
• Cooked meals
• Sandwich fillings

Question 5

Growth characteristics of S.aureus?

Answer 5

-Can grow in wide range of temperatures
(7 o C -48 o C)

-pH (4.2-9.3)

-NaCl concentrations (up to 15%)- Ham has a 3% salt concentration

Question 6

Example of outbreak of S.aureus?

Answer 6

Chocolate milk = source of outbreak in Kentucky, USA
-Chocolate milk contaminated and stored at too high temp for 5 hrs before
pasteurisation
- Pasteurisation killed the bacteria but had no effect on SEs

Question 7

Why did people still get sick if milk was pasteurized?

Answer 7

Once milk has presence of S.aureus from eg hands of human or cow with mastitis and THEN milk was left unrefrigerated 7 degrees. Pasteurization kills bacteria but once enterotoxin has formed when room temp, it can’t be killed by pasteurization

Question 8

where does S.aureus come from?

Answer 8

Main sources of contamination are humans
* Handlers contaminate food via manual contact
* Via respiratory tract (sneezing & coughing)

In raw meat and milk, contamination more frequently caused by animal
carriage or infection e.g. mastitis

Question 9

How many different types of Staphylococcal Enterotoxins?

Answer 9

14 Staphylococcal Enterotoxins eg. SE A,B,C1,C2 and C3

Question 10

which are major Staphylococcal Enterotoxins?

Answer 10

SEA-C

Question 11

Why do Staphylococcal Enterotoxins thrive ? Hint there 4 reasons

Answer 11

1. Highly stable e.g heat stable
   2.Resist pepsin and trypsin activity in digestive tract (which would normally kill bacteria)
   3.active at low ph
   4.active at high salt

Question 12

Are genes encoding SEs located
on mobile genetic elements?

Answer 12

Yes, Genes encoding SEs are mostly located
on mobile genetic elements.

Question 13

Example of Mobile Genetic Elements?

Answer 13

-Prophage
-plasmid
-pathogenicity islands

Question 14

What Mobile Genetic Elements are associated with:
SEA gene
SEC bov gene

Answer 14

-sea carried by temperate phages

-SECbovine is encoded by a gene
located on a pathogenicity island

Question 15

In food sample, how many S.aureus strains are enterotoxigenic?

Answer 15

15-25%

Question 16

How many S.aureus strains are enterotoxigenic from milk of
cows with mastitis ?

Answer 16

72%

Question 17

For gene expression leading to S.enterotoxins what level of S.aureus do you need?

Answer 17

More than 10 5 cfu/g
Need high density of S.aureus colonies for gene expression for S. Enterotoxins

Question 18

What has an inhibitory effect on S.enterotoxins ?

Answer 18

Glucose