PMB: Staphylococcus 16 Flashcards
1
Q
Describe the characterisitics of staphylococcus
A
- Spherical Gram positive cocci
- Catalyse positive
- 2XH2O2 –(catalyse)–> 2XH2O + O2
- Resistant to dry conditions and high salt concentrations
- 40 different species
2
Q
What are the 3 main medical species?
A
- S. aurues
- S. epidermidis
- S. Saprophyricus
3
Q
How do species of staphylococcus differ?
A
- Hameloysis
- Coagulase
- Clumping factor
- CAMP-reaction
4
Q
What is haemolysis?
A
The ability to lyse RBCs on blood agar
5
Q
What is the haemolytic profile of the staphylococcus?
A
- S. Aureus: haemolytic
- S. epidermidis and S. soprophyticus: Non-haemolytic
6
Q
What are Staphylococcus divided into?
A
Coagulase positive (S.aurues) and Coagulase negative (the others)
7
Q
What is coagulase?
A
It is NOT an enzyme
Its is a extracellular protein which binds to prothrombin to form staphylothrombin
8
Q
What does coagulase do?
A
- This binding activates its protease activity of thrombin and causes the conversion of fibrinogen to fibrin
- It is important in boil and pimple formation
9
Q
What is clumping factor
Where is it found?
What does it do?
A
- Clumping factor is a protein attached to the cell wall of S.Aureus.
- Clumping factor negative in S. saprophyticus and S. epidermidis
- It mediates binding of bavteria to fibrinogen, found in different tissues —> meidates attachment
- •Mixing of plasma with S. aureus on slide results in clumping of suspension; bacteria-bound clumping factor crosslinks bacteria via fibrinogen
10
Q
Describe the CAMP test
A
- CAMP test is used to identify B-haemolytic streptococci e.g. S.agallactiae based on their production of a compound CAMP.
- CAMP enlarges the haemolysis area formed by B- haemolysis/ B toxin from S.aureus
- S.aureus is known to produce different toxins including toxic shock syndrome toxin (TSST)
- Increased zone of haemolysis between S. aureus and Streptococcus agalactiae on blood agar
- S. aureus produces variety of toxins: e.g. a, b, g, TSST
- ß-toxin: sphingomyelinase: lyses and damages red blood cells
- In presence of CAMP factor from S. agalactiae, lysis of ß-toxin-damaged red blood cells
11
Q
Complete the table
A
12
Q
S.Epidermiditis:
- Where found?
- Infects?
A
- Found in the flora
- Opportunistic pathogen (take advantages of opportunities not usually there e.g. hosts with weakened immune syster
- Infection of immunocompromised patients
- Colonization on biomeidcal devices by biofilm formation
- intravasucular lines
- Prosthetic valves
- Require exchange of contaminated devices
13
Q
S. Saprophyticus
- Where found?
- Infects which body parts?
- Causes?
A
- Found in noraml flora of skin in around 25% of the population
- Colonizes in the GI tract, genitals and skin
- Commonly causes UTIs (especially in young women after intercourse.
- Can adhere to urinary tract and form urease
- 2nd most common cause of UTIs
- Burning sensation when urinating
- More freuently urinatinfg
- foul-smelling, cloudly, bloody urine
14
Q
S.Aureus
- Where found
- Causes
A
- Present in nose of 30% of healthy individuals. May also be found on skin
- Different variety of infections:
- Local, usually cutanoues: invasion thrrough wounds, glands and follicles
- Intoxication
- Wound infections/ Infections of indwelling devises
15
Q
Describe some localised, cutaneous S.aureus infections
A
- •Boil; walled-off site of skin infection with central pus formation
- •Folliculitis: superficial inflammation of hair follicle; often occurring as pimples
- •Furuncle: more serious infection of hair follicle: localized region of pus surrounded by inflamed tissue
- •Carbuncle: hard, round, deep inflammation of tissue under skin; extensive damage
- •Impetigo: infection of the top layers of skin; most common in children
