Unit 5: Staphyloccus Aureus

Question 1

What are the 5 general characteristics of a foodborne intoxication

Answer 1

1. toxin 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 minutes after ingestion
5. febrile symptoms are not present

Question 2

give the main characteristics of staphylococcus aureus (7)

Answer 2

1. gram positive cocci
2. single cells or grape like clusters
3. non motile, non capsular
4. non spore forming, sensitive to heat
5. facultative anaerobes but grow rapidly under aerobic conditions
6. mesophiles (7-48 deg C) but rapidly between 20-37 deg C.
7. can grow low aw, low pH and under high salt and sugar concentrations

Question 3

T or F: S aureus can grow under several adverse conditions but are poor competitors against other microorganisms therefore do very well when adverse environments give them competitive advantage

Answer 3

T

Question 4

Provide an explanation of S aureus Genomics

Answer 4

Multilocus sequencing typing (MLST) is commonly used to define the sequence type (ST) or allelic profile based on the sequences of 7 housekeeping genes found in all strains of S. aureus.
This was once done by Sanger Sequencing, but currently, ST is almost exclusively defined by extracting the sequence of these 7 genes from the whole genome sequence.
If a group of STs share at least 5 of 7 alleles, the group of STs can be defined as a clonal complex (CC).

Question 5

what is an enterotoxin

Answer 5

a toxin that acts on the GI tract

Question 6

what is an endotoxin

Answer 6

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

Question 7

what is an exo toxin

Answer 7

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

Question 8

what are exfoliative toxins

Answer 8

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

Question 9

T or F: all Sa enterotoxins are also exotoxins

Answer 9

True

Question 10

Explain some characteristics of the toxin expression of S aureus

Answer 10

1. enterotoxins are made throughout most of the exponential growth phase
2. enterotoxins production can be inhibited by the presence of glucose
3. endotoxins may be involved in quroum sensing in Sa

Question 11

T or F: The stability of the staphyloccus toxin is unique because it is heat stable ie. not destroyed by boiling or canning

Answer 11

True

Question 12

The S aureus stimulates ..

Answer 12

the vagus and sympathetic nerves

Question 13

what is the main environmental source of S aureus

Answer 13

people. we have it in our skin, interior of our nose. it can be spread by direct contact, skin fragments and respiratory droplets (blood supply) and also found in erupted acne in humans.

Question 14

T or F: S aureus cannot acquire resistance to heavy metals and antiobiotics

Answer 14

False, it can

Question 15

T or F: S aureus invade human cells and live intracellularly

Answer 15

True

Question 16

Provide an example on how animals can be carriers of Sa

Answer 16

bovine mastitis cause + infections in agricultural animals – contaminate milk and dairy products – contaminate milkers and facilities – may survive pasteurization

Question 17

most food contamination of S aureus is traced to humans during….. and how?

Answer 17

food preperation. organism finds its way onto food, food is not properly refrigerated, organism grows and produces toxin, people eat food, people get sick.

Question 18

what are some contributing factors to food contamination with s aureus

Answer 18

1. inadequate refrigeration
2. preparing foods too far in advance
3. poor personal hygiene (just wash your hands)
4. inadequate cooking
5. prolonged use of warming plates (ie buffet)

Question 19

List some characteristics of S aureus disease

Answer 19

Very quick onset (30 minutes), mean incubation is 4.4 hours, 10hrs is maximum time to onset
Self-limiting and recovery in 24-48 hours
Most cases not reported (unless highly publicized, i.e. on an international jetliner)
Outbreaks are seasonal
People prepare foods for picnics the night before, leave the food on a table in the sun all afternoon
There is never any fever
Almost everyone vomits, other symptoms can have nausea, diarrhea, and abdominal pain
Death is very rare
Purified toxin is considered a bioterrorism agent

Question 20

What is Methicilin resistant Sa (MRSA)

Answer 20

MRSA strains carry the mecA gene
MRSA is the causative agent of soft tissue and skin infections, along with necrotizing fasciitis
MRSA was identified in cows in the 1970s
Found soon after, and widespread, in pigs
Found in 0.4-12% of retail meat, they did carry the enterotoxin gene
Food could be a source of extraintestinal infection
Food handlers get infected through cuts or skin lesions

Question 21

how to prevent s aureus?

Answer 21

Hand washing, glove wearing, and avoidance of hiring food prep. workers with active skin infections
People with respiratory disease, acute facial acne, skin rashes, boils, and cuts in hands should not handle food
Adequate refrigeration, or continued heating of prepared food
Re-heating is not helpful
Preservatives could be used to kill or arrest growth of the organism