PMB: Staphylococcus 16

Question 1

Describe the characterisitics of staphylococcus

Answer 1

• Spherical Gram positive cocci
• Catalyse positive
  
  • 2XH2O2 –(catalyse)–> 2XH2O + O2
• Resistant to dry conditions and high salt concentrations
• 40 different species

Question 2

What are the 3 main medical species?

Answer 2

• S. aurues
• S. epidermidis
• S. Saprophyricus

Question 3

How do species of staphylococcus differ?

Answer 3

• Hameloysis
• Coagulase
• Clumping factor
• CAMP-reaction

Question 4

What is haemolysis?

Answer 4

The ability to lyse RBCs on blood agar

Question 5

What is the haemolytic profile of the staphylococcus?

Answer 5

• S. Aureus: haemolytic
• S. epidermidis and S. soprophyticus: Non-haemolytic

Question 6

What are Staphylococcus divided into?

Answer 6

Coagulase positive (S.aurues) and Coagulase negative (the others)

Question 7

What is coagulase?

Answer 7

It is NOT an enzyme

Its is a extracellular protein which binds to prothrombin to form staphylothrombin

Question 8

What does coagulase do?

Answer 8

• This binding activates its protease activity of thrombin and causes the conversion of fibrinogen to fibrin
• It is important in boil and pimple formation

Question 9

What is clumping factor

Where is it found?

What does it do?

Answer 9

• 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

Question 10

Describe the CAMP test

Answer 10

• 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

Question 11

Complete the table

Answer 11

Question 12

S.Epidermiditis:

1. Where found?
2. Infects?

Answer 12

1. Found in the flora
2. 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

Question 13

S. Saprophyticus

1. Where found?
2. Infects which body parts?
3. Causes?

Answer 13

1. Found in noraml flora of skin in around 25% of the population
2. Colonizes in the GI tract, genitals and skin
3. Commonly causes UTIs (especially in young women after intercourse.
4. Can adhere to urinary tract and form urease
5. 2nd most common cause of UTIs
   
   1. Burning sensation when urinating
   2. More freuently urinatinfg
   3. foul-smelling, cloudly, bloody urine

Question 14

S.Aureus

1. Where found
2. Causes

Answer 14

1. Present in nose of 30% of healthy individuals. May also be found on skin
2. Different variety of infections:
   
   • Local, usually cutanoues: invasion thrrough wounds, glands and follicles
   • Intoxication
   • Wound infections/ Infections of indwelling devises

Question 15

Describe some localised, cutaneous S.aureus infections

Answer 15

• •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

Question 16

What are some examples of intoxications caused by S.aurues?

Answer 16

• Staphylococcal toxic shock syndrome (STSS); superantigen
• Exfoliative Intoxications; proteases
• Staphylococcal food poisoning; enterotoxins; superantigens

Question 17

Discuss STSS

Answer 17

• •Highest incidence in 1980s by growth of S. aureus in high-absorbent tampon
• •absorption of the superantigen-toxin into the blood stream
• •Complication after surgery using tampons
• •Can be caused at any body site infected by S. aureus
• •Symptoms include high fever and profound malaise
• •Extreme hypotension results in organ failure (kidneys, liver)

Question 18

Disccuss food posioning

Answer 18

• •Contamination of food during processing
• •Amino acids and B vitamins needed (animal origin foods)
• •High osmotic pressure foods (reduces competition)
• •Heat-stable toxin (superantigen) produced during growth of S. aureus in food
• •Eight enterotoxins (A-E, G-I)
• •Some strains produce more than one toxin
• •Multiplication of bacteria in food to produce enough toxin to cause illness (>106 CFU/g)
• •Nausea, vomiting, cramping, diarrhea
• •rarely fatal

Question 19

Describe exfoliation intoxications

Answer 19

• •Staphylococcal scalded skin syndrome (SSSS)
• •Occurs primarily in newborns and children up to 4 years
• •Superficial layers of the skin peel off because of Exfoliative toxin
• •Exfoliatin A, and B are serine proteases that specifically cleave desmoglein 1 in stratum granulosum of epidermis
• •Exfoliatin A produced by strains infected with bacteriophage type II
• •Exfoliatin B encoded by plasmid
• causes separation of the dermal and epidermal layers of the skin

Question 20

Discuss the isolation and testing off staphyolococcal

Answer 20

• •In a lesion: direct Gram stain
• •Streaking material from the clinical specimen onto mannitol salt agar containing 7.5% sodium chloride
• •Tests for catalase and coagulase production
• •Test for agglutination with latex particles coated with immunoglobulin G and fibrinogen which bind protein A and the clumping factor on the bacterial cell surface
• •If S. aureus confirmed, test with oxacillin for MRSA strains

Alternatively:

• PCR testing for presence of mecA gene
• Agglutination assay with latex beads coated with antibodies against PBP 2a

Question 21

Describe treatment

Answer 21

• •Hospital strains of S aureus are often resistant to many different antibiotics
• •90% clinical isolates resistant to penicillins by production of enzyme penicillase that cleaves ß-lactam ring
• •MRSA strains resistant to all ß-lactam antibiotics and often to aminoglycosides and fluoroquinolones
• •MRSA strains carry in genome mecA gene, encoding a transpeptidase (penicillin-binding protein (PBP 2a)) not affected by ß-lactam antibiotics
• •Glycopeptides, like vancomycin and teicoplanin, are antibiotics of choice for treatment of MRSA strains
• •New antibiotic for treatment of MRSA strains: linezolid

Question 22

Why is there differences in resistance

Answer 22

• High differences in MRSA prevalence between European countries with comparable clinical standards
• Differences due to different screening, isolation and transport of infected patients, sanitation of infected areas, visitors

Question 23

Describe prophylaxisis

Answer 23

• •Testing of all incoming patients for being carriers of MRSA strains
• •Separation of patients who carry MRSA strains
• •Exclusively for the protection of other patients or the medical staff
• Recommendations for visitors and staff dependent on modes of transmission (aerosols, contact)