10 - Streptococci

Question 1

What are the shape of streptococci?

Answer 1

Gram positive cocci chains

String of pearls

Question 2

How are streptococci classified into three groups by haemolysis?

Answer 2

- Alpha/Viridans (Green) : partial haemolysis

- Beta (White) : complete haemolysis

- Gamma: no haemolysis

Question 3

What are Viridans streptococci?

Answer 3

• Alpha Haemolysis = partial haemolysis
• Mainly found in mouth

Question 4

What else can streptococci be identified as apart from haemolysis?

Answer 4

• Lancefield
• Sherman group

Question 5

What infection does strep pyogenes normally cause?

Answer 5

• Sore throat like tonsillitis and pharyngitis
• Can cause necrotising facitis

Question 6

What shape and gram are staphylococcus?

Answer 6

- Clustered gram positive cocci

• Can be coagulase negative or positive

Question 7

Identify and describe 3 virulence factors of streptococcus pyogenes.

Answer 7

• Streptolysin O and S: lysis of RBC, platelets, neutrophils
• Streptokinase: resolution of clots

Question 8

What is the full name and classification of Strep.Pyogenes?

Answer 8

Lancefield Group A Beta-Haemolytic Streptococcus

Question 9

What is streptococcal pharyngitis?

Answer 9

• Group A strep on throat swab
• Step.Pyogenes
• Untreated patients produced M protein antibody

Question 10

What are some complications of streptococcal pharyngitis?

Answer 10

• Scarlet fever
• Rheumatic fever

Question 11

What is scarlet fever?

Answer 11

Acute condition

Question 12

What is acute rheumatic fever?

Answer 12

Causes inflammation of own tissues

Question 13

What are some symptoms of rheumatic fever?

Answer 13

Question 14

What is acute post-streptococcal glomerulonephritis?

Answer 14

Question 15

What are some skin infections that Strep.Pyogenes can cause?

Answer 15

• Impetigo
• Erysipelas
• Cellulitis
• Necrotising fascitis

Question 16

What is impetigo?

Answer 16

• Streptococcus pyogenes skin infection, often occurring in children of 2-5 years
• Initial skin colonisation, followed by intradermal inoculation
• Most common cause of glomerulonephritis

Question 17

What is erysipelas?

Answer 17

Question 18

What is cellulitis?

Answer 18

Question 19

What is necrotising fascitis?

Answer 19

• Rapid extensive necrosis
• Severe pain before clinical changes
• Severe mortality so fast debridement and sweep test needed

Question 20

What is toxic shock syndrome?

Answer 20

Question 21

What is the pathogenesis of toxic shock syndrome?

Answer 21

• M protein-fibrinogen complexes bind to leukocytes that degranulate and release hydrolytic enzymes to break down endothelium
• Vascular leakage and hypercoagulability leading to hypotension, DIC and organ damage

Question 22

What is the coagulase test?

Answer 22

Clotting means Staph Aureus

Question 23

What is vegetation?

Answer 23

• Growth of bacteria on heart valve forming infected mass and leading to endocarditis
• Collection of fibrin, platelets and inflammatory cells

Question 24

What is a biofilm?

Answer 24

Microbial communities attached to surfaces and encased in an extracellular matrix of microbial origin

Question 25

What classes of bacteria are mainly responsible for nosocomial infections and why?

Answer 25

- Staphylococci and enterococci as they produce biofilms on surfaces, e.g catheter, prosthetic devices - Both are commensal inhabitants

Question 26

What bacteria are mainly connected to device-associated infections?

Answer 26

- ***CoagNeg staphylococci*** e.g S.epidermidis in catheters ***- S.Aureus*** (more acute than above as they can provoke more of a host immune response)

Question 27

Why is the only way to treat endocarditis by replacement of heart valve?

Answer 27

- Cannot treat with antibiotics as biofilm and deep bacteria are dormant - Superficial bacteria can easily embolise and lead to sepsis

Question 28

How do biofilms confer bacterial resistance?

Answer 28

- Multidrug tolerance - Matrix restricts penetration and diffusion of antimicrobials - Bacteria in biofilm can secrete beta-lactamases and increase expression of MDR efflux pumps - Quorum sensing - Presence of persisters

Question 29

What do you have the risk of developing if you are born with a bicuspid aortic valve?

Answer 29

- Endocarditis - Abnormal flow of blood over valve so greater risk of microbes in blood sticking to valve and setting up local infection within biofilm - Endocardium normally non-sticky but the blood flow can damage it so it get's vegetation. Microorganisms in blood can then stick and invade this vegetation causing endocarditis

Question 30

Why can S.Aureus cause endocarditis with an absence of initial vegetation to stick to?

Answer 30

Posesses fibronectin binding proteins so can bind to intact endothelium and infect uninfected endocardium

Question 31

What are the three hallmarks of endocarditis?

Answer 31

1. Constitutional symptoms which are cytokine mediated 2. Local spread of infection causing destruction of myocardium 3. Distal blood borne septic embolisation

Question 32

What is the biofilm hypothesis?

Answer 32

Question 33

What are clinical features of endocarditis?

Answer 33

- Fever - Heart murmur - Embolic features (Janeway Lesions, Splinter Haemorraghe, Roth Spots in eyes, Osler Nodes) due to small bits of vegetation breaking off and blocking small capillaries and setting up infection there

Question 34

What are the following symptoms of endocarditis: - Janesway Lesions - Oslers Nodes - Splinter Haemorrhages - Roth spots in eye

Answer 34

Question 35

How is endocarditis diagnosed?

Answer 35

**Duke Criteria:** - Standard infection features e.g fever - Cardiac features e.g murmur - Microbiological features e.g positive blood culture - Embolic features of vegetation