Unit 5: Staphyloccus Aureus Flashcards
What are the 5 general characteristics of a foodborne intoxication
- toxin produced by a pathogen while growing in the food
- the toxin can be heat liable or heat stable
- ingestion of a food containing active toxin, not viable cells, is necessary for poisoning
- symptoms generally occur quickly as early as 30 minutes after ingestion
- febrile symptoms are not present
give the main characteristics of staphylococcus aureus (7)
- gram positive cocci
- single cells or grape like clusters
- non motile, non capsular
- non spore forming, sensitive to heat
- facultative anaerobes but grow rapidly under aerobic conditions
- mesophiles (7-48 deg C) but rapidly between 20-37 deg C.
- can grow low aw, low pH and under high salt and sugar concentrations
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
T
Provide an explanation of S aureus Genomics
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).
what is an enterotoxin
a toxin that acts on the GI tract
what is an endotoxin
a toxin that is structurally associated with the bacterial cell (LPS)
what is an exo toxin
a toxin that is usually secreted into the extracellular fluid but can be intracellular or injected directly into eukaryotic cells
what are exfoliative toxins
dermolytic exotoxins produced exclusively by Sa that cause the symptoms of impetigo or scaled skin syndrome
T or F: all Sa enterotoxins are also exotoxins
True
Explain some characteristics of the toxin expression of S aureus
- enterotoxins are made throughout most of the exponential growth phase
- enterotoxins production can be inhibited by the presence of glucose
- endotoxins may be involved in quroum sensing in Sa
T or F: The stability of the staphyloccus toxin is unique because it is heat stable ie. not destroyed by boiling or canning
True
The S aureus stimulates ..
the vagus and sympathetic nerves
what is the main environmental source of S aureus
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.
T or F: S aureus cannot acquire resistance to heavy metals and antiobiotics
False, it can
T or F: S aureus invade human cells and live intracellularly
True
Provide an example on how animals can be carriers of Sa
bovine mastitis cause + infections in agricultural animals – contaminate milk and dairy products – contaminate milkers and facilities – may survive pasteurization
most food contamination of S aureus is traced to humans during….. and how?
food preperation. organism finds its way onto food, food is not properly refrigerated, organism grows and produces toxin, people eat food, people get sick.
what are some contributing factors to food contamination with s aureus
- inadequate refrigeration
- preparing foods too far in advance
- poor personal hygiene (just wash your hands)
- inadequate cooking
- prolonged use of warming plates (ie buffet)
List some characteristics of S aureus disease
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
What is Methicilin resistant Sa (MRSA)
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
how to prevent s aureus?
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
