10 - Streptococci Flashcards
What are the shape of streptococci?
Gram positive cocci chains
String of pearls
How are streptococci classified into three groups by haemolysis?
- Alpha/Viridans (Green) : partial haemolysis
- Beta (White) : complete haemolysis
- Gamma: no haemolysis
What are Viridans streptococci?
- Alpha Haemolysis = partial haemolysis
- Mainly found in mouth
What else can streptococci be identified as apart from haemolysis?
- Lancefield
- Sherman group
What infection does strep pyogenes normally cause?
- Sore throat like tonsillitis and pharyngitis
- Can cause necrotising facitis
What shape and gram are staphylococcus?
- Clustered gram positive cocci
- Can be coagulase negative or positive
Identify and describe 3 virulence factors of streptococcus pyogenes.
- Streptolysin O and S: lysis of RBC, platelets, neutrophils
- Streptokinase: resolution of clots
What is the full name and classification of Strep.Pyogenes?
Lancefield Group A Beta-Haemolytic Streptococcus
What is streptococcal pharyngitis?
- Group A strep on throat swab
- Step.Pyogenes
- Untreated patients produced M protein antibody
What are some complications of streptococcal pharyngitis?
- Scarlet fever
- Rheumatic fever
What is scarlet fever?
Acute condition
What is acute rheumatic fever?
Causes inflammation of own tissues
What are some symptoms of rheumatic fever?
What is acute post-streptococcal glomerulonephritis?
What are some skin infections that Strep.Pyogenes can cause?
- Impetigo
- Erysipelas
- Cellulitis
- Necrotising fascitis
What is impetigo?
- Streptococcus pyogenes skin infection, often occurring in children of 2-5 years
- Initial skin colonisation, followed by intradermal inoculation
- Most common cause of glomerulonephritis
What is erysipelas?
What is cellulitis?
What is necrotising fascitis?
- Rapid extensive necrosis
- Severe pain before clinical changes
- Severe mortality so fast debridement and sweep test needed
What is toxic shock syndrome?
What is the pathogenesis of toxic shock syndrome?
- 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
What is the coagulase test?
Clotting means Staph Aureus
What is vegetation?
- Growth of bacteria on heart valve forming infected mass and leading to endocarditis
- Collection of fibrin, platelets and inflammatory cells
What is a biofilm?
Microbial communities attached to surfaces and encased in an extracellular matrix of microbial origin
What classes of bacteria are mainly responsible for nosocomial infections and why?
- Staphylococci and enterococci as they produce biofilms on surfaces, e.g catheter, prosthetic devices
- Both are commensal inhabitants
What bacteria are mainly connected to device-associated infections?
- CoagNeg staphylococci e.g S.epidermidis in catheters
- S.Aureus (more acute than above as they can provoke more of a host immune response)
Why is the only way to treat endocarditis by replacement of heart valve?
- Cannot treat with antibiotics as biofilm and deep bacteria are dormant
- Superficial bacteria can easily embolise and lead to sepsis
How do biofilms confer bacterial resistance?
- 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
What do you have the risk of developing if you are born with a bicuspid aortic valve?
- 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
Why can S.Aureus cause endocarditis with an absence of initial vegetation to stick to?
Posesses fibronectin binding proteins so can bind to intact endothelium and infect uninfected endocardium
What are the three hallmarks of endocarditis?
- Constitutional symptoms which are cytokine mediated
- Local spread of infection causing destruction of myocardium
- Distal blood borne septic embolisation
What is the biofilm hypothesis?
What are clinical features of endocarditis?
- 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
What are the following symptoms of endocarditis:
- Janesway Lesions
- Oslers Nodes
- Splinter Haemorrhages
- Roth spots in eye
How is endocarditis diagnosed?
Duke Criteria:
- Standard infection features e.g fever
- Cardiac features e.g murmur
- Microbiological features e.g positive blood culture
- Embolic features of vegetation
