Staphylococcus aureus

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  • Created by: Rose
  • Created on: 19-05-14 08:40
Is S. aureus gram + or gram -?
Gram +
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How does S. aureus grow?
Clusters
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How do we diagnose gram + cocci?
Aerobic / Non-aerobic? ---> Catalase Test
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Are streptococci catalase positive or negative?
NEG
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Are staphylococci catalase positive or negative?
POS
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Name three common human pathogens of the Staphylococcus genus
S. aureus, S. epidermis, S. saprophyticus
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What colour colonies does S. aureus produce on blood agar?
Golden yellow colonies
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Why?
Hemolytic
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What size are the colonies formed?
Pinhead
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Which selective media is used to grow S. aureus?
Mannitol Salt Agar (MSA)
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Why is it selective for S. aureus?
S. aureus can withstand its high salt concentration. Other bacterial growth is inhibited
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What colour colonies does S. aureus form on MSA?
Yellow colonies
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COAGULASE TEST
COAGULASE TEST
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What does the coagulase test do?
Differentiate S. aureus from other Staphylococci
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Which reaction does coagulase catalyse?
Fibrinogen ---> Fibrin
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ADD PLASMA + ORGANISM ---> CHECK FOR CLUMPING (+)
ADD PLASMA + ORGANISM ---> CHECK FOR CLUMPING (+)
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Is S. aureus coagulase negative or positive?
POSITIVE
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DNAase Test : Streak organism on DNA containing media, check for clearing of media
DNAase Test : Streak organism on DNA containing media, check for clearing of media
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Is S. aureus DNAase positive or negative?
POSITIVE
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Is S. aureus mannitol fermenting
Yes, S. aureus is mannitol fermenting
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What colour change is seen in mannitol fermentation?
Red ---> Yellow
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What types of infections can S. aureus cause?
SSTI, Food poisoning, Sometimes serious e.g. Bone, blood, endocarditis...
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S. aureus infection can be endogenous or exogenous
S. aureus infection can be endogenous or exogenous
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What can be the exogenous sources of S. aureus?
Another person (infected OR carrier), inanimate object (food, medical instruments)
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Modes of Transmission for S. aureus?
Contact (e.g. skin - skin in impetigo), Inhalation, Ingestion (food poisoning)
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What are the three main virulence factors for S. aureus?
Adherence, Enzymes, Toxins in SOME strains
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How does S. aureus adhere?
MSCRAMMs
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What does MSCRAMM stand for?
Microbial Surface Components Recognising Adhesive Matrix Molecules
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MSCRAMMS are strain dependent and thus organ specific
MSCRAMMS are strain dependent and thus organ specific
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Name three enzymes S. aureus possesses
Coagulase, Lipase, Protein A
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What does coagulase do?
Produces fibrin barrier around bacteria, helps in immune evasion
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What does lipase do?
Digest host tissue, aid invasion of bacteria
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What does protein A do?
Binds Fc portion of antibody (not variable region), impairs antibody function and helps with immune evasion
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What is the name of the toxin S. aureus possesses?
Panton Valentine Leucocidin (PVL)
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Is PVL an exotoxin or an endotoxin?
Exotoxin
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PVL structure and genes?
A pore like structure (made up from two genes, LukS and LukF)
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How does PVL harm the host?
Inserts itself into leucocytes, inflammatory mediators pour out, DAMAGE TO SURROUNDING TISSUE
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Which toxin is carried by ~65% of S. aureus strains?
Enterotoxin
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Which is the most common enterotoxin?
Type A
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What are the two effects of enterotoxin?
1. Vomiting, 2. Superantigen
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How do super antigens work?
Link up MHC with TCR WITHOUT ANTIGEN PROCESSING!
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What does this super antigen cause?
Shock like symptoms (Hyper-exaggerated immune response)
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What is TSST-1?
Toxic Shock Syndrome Toxin
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TSST-1 ACTS AS A SUPERANTIGEN
TSST-1 ACTS AS A SUPERANTIGEN
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* Staphylococcal Food Poisoning*
* Staphylococcal Food Poisoning*
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What is the source of the bacteria that contaminates the food?
The food handler
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What happens once the bacteria is in the food and what makes it so dangerous?
Multiplies in food, produces TOXIN which can't be removed by heating of the food
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When do symptoms (nausea, vomiting) arise?
1-6 hours after ingestion
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Card 2

Front

How does S. aureus grow?

Back

Clusters

Card 3

Front

How do we diagnose gram + cocci?

Back

Preview of the front of card 3

Card 4

Front

Are streptococci catalase positive or negative?

Back

Preview of the front of card 4

Card 5

Front

Are staphylococci catalase positive or negative?

Back

Preview of the front of card 5
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