Staphs/ Streps (W1)

Question 1

LO’s

Answer 1

1. Describe the classification of Streptococci and Staphylococci and the diseases they cause.
2. Describe the virulence factors of Streptococcus pyogenes in the development of sepsis.

Question 2

Which toxic mediated diseases (diseases in places other than infection site, due to toxin excretion) can Staph Aureus cause?

Answer 2

1. Scalded Skin Syndrome
2. Food Poisoning (s.aureus growing in food releases toxins in the food)
3. Toxic Shock

​Need to learn this by heart

Question 3

Which suppurative (production of pus) infections can Staph Aureus cause?

Answer 3

1. Impetigo: bacterial skin infection causing blisters (containing pus) and sores (marks).
2. Folliculitis: inflammation of the hair follicles.
3. Carbuncle / Furuncles: Carbuncle is connected boils. Furuncle is one boil containing pus.
4. Epyema: pus in the pleaural cavity/space.
5. Endocarditis: infection of the endocardium, the inner lining of the heart.
6. Septic Arthritis: inflammation of a joint caused by infection.
7. Osteomyelitis: bone infection.
8. Pneumonia: inflammation of the lungs.

Question 4

What other things can Staph Aureus cause?

Answer 4

• UTIs
• Wound Infections
• Catheter Infections- s.aureus can colinise catheters
• Cellulitis: bacterial skin infection causing redness and warmth of the skin.
• Prosthetic devices
• Maybe eczema
• Sepsis

Question 5

In what percentage of hospital workers is Staph Aureus present?

Answer 5

90%- maybe

Question 6

What are the pathogenicity factors of some Staph Aureus?

Answer 6

1. Capsule: prevents it being phagocytosed.
2. Protein A: binds to IgG stops activation of complement pathways so opsins not made.
3. Fibronectin Binding Protein: aids binding to host cell
4. Cytolytic Exotoxins: haemolysins that destroy red blood cells
5. Panton-Valentine Leukocidin: lyses polymorphonuclear lymphocytes (immune cells)

Question 7

How does Stap Aureus caume damage using toxins?

Answer 7

By over-stimulating immune system:

1. Enterotoxins (A,B,C,D,E and G) half of all s.aureus isolates cause vomiting and diarrheas
2. Toxic shock syndrome toxin (TSST-1)
3. Exfoilatin toxin

Question 8

Describe Methicillin Resistant S. Aureus (MRSA)?

Answer 8

Don’t respond to normal antibiotics: flucloxacillin will not work.

Try glycopeptides (e.g. vancomycin).

Try tetracycline / 3rd generation penicillins.

Question 9

How are streptococci classified by their haemolytic properties? draw the portioned agar plate on slide

Answer 9

Growth on blood agar allow determination of heamolytic type, different strep do different things to the blood:

1. a-haemolytic streptococci cause haemoglobin to change colour
2. b-haemolytic lyse red blood cells
3. g-haemolytic cause no change

Question 10

How are streptococci classified by their serological (how they react to antibodies) properties?

Answer 10

• Mainly for b-haemolytic streptococci based on cell wall polysaccharide
• Clinically most important b-haemolytic streptococci are group A and B

Question 11

Describe Group A Streptococcus Pyogenes

Answer 11

Can bind to pharyngeal mucosa through actions of :

–Protein Fm

–Lipotechoic acid

–M antigen

Question 12

What are the possible pathogenicity factors of Group A Streptococcus Pyogenes?

Answer 12

1. Streptolysin O and S: lysis of eukaryotic cells
2. Hyaluronidase: breaks down connective tissues
3. Pyogenic Toxins: superantigens, responsible for many of the clinical manifestations
4. Streptodornases: breakdown DNA in lysed tissues
5. Streptokinase: lysis of clots, facilitates spread of organism
6. C5A peptidase: inactivates complement

Question 13

How is pharyngitis diagnosed?

Answer 13

Rapid onset sore throat (Streptococcal Pharyngitis) usually starts quickly and can cause severe pain when swallowing.

Correct diagnosis is important for strep throat so that Rheumatic fever and Rheumatic Heart Disease are to be avoided.

• Use the Fever Pain Index for diagnosis.
• Also do rapid antigen test.

Question 14

How is the Fever-Pain Index calculated?

Answer 14

The criteria are: score 1 point for each (so maximum score of 5)

• Fever over 38°C.
• Purulence (pharyngeal/tonsillar exudate).
• Attend rapidly (3 days or less)
• Severely Inflamed tonsils
• No cough or coryza

Question 15

How is pharngitis due to strep pyogenes treated?

Answer 15

1. Phenoxymethylpenicillin - Penicillin.
2. Amoxicillin
3. There is no vaccine

Question 16

How can Streptococcus Pyogenes cause rheumatic fever?

Answer 16

•Post Strep Pharyngitis complications

•Acute rheumatic fever

•Autoimmune reaction (cross reactivity between M-protein and human cell surface proteins)

•Symptoms: 1-5 weeks after streptococcal pharyngitis /Fever / Rash / Carditis / Arthritis / CNS manifestations

•1 in 3 people with acute RF will develop Rheumatic heart disease

Question 17

Describe Strep Pneumoniae?

Answer 17

•Gram +ve diplococci

•Present in nasopharynx of healthy individuals

•a-haemolytic

•Causative agent of pneumococcal disease

Question 18

What can Strep Pneumoniae cause?

Answer 18

• Bacterial Pneumonia - leading cause of Community Acquired Pneumonia
• Otitis media
• Pnuemococcal Bacteremia
• Pneumococcal Sepsis
• Pneumococcal Meningitis

Question 19

What are the pathogenicity factors of s.pneumoniae?

Answer 19

•Capsule: antiphagocytotic

•Pili: enable attachment to cells of upper respiratory tract

•Choline binding protein: facilitates binding to carbohydrate of cells in URT

•Autolysins: facilitate breakdown of cell to allow release of pnuemolysin

•Pneumolysin: breakdown of eukaryotic cells

Question 20

What is the Strep Pneumoniae vaccine’s trade name?

Answer 20

• In the UK a single dose of a 13 polyvalent vaccine at 2 years is given
• Trade name is Prevanar 13

Question 21

How do Streptococcus and Staphylcoccus look different under a microscope?

Answer 21

• Staph is arranged in grape like clusters.
• Strep is arranged in a chain of round cells.