Microbiology Flashcards
What is Rheumatic fever
an immune-mediated, post-streptococcal disease that affects the joints, heart, brain and skin
Morphology of Strep. pyogenes
- Gram positive in chain
- Catalse -ve
- Group A Haemolysis (GAS)
What is the pathogenesis of Strep. pyogenes
- Pyogenic (tonsilitis, cellulitis)
- Toxigenic (toxic shock syndrome)
- Immune mediated (post streptococcal diseases - Acute glomerulonephritis, Rheumatic fever)
What is the morphology of Staph. aureus
Gram positivie cocci, cluster, catalse +ve
How to differentiate Group A & Group B beta-haemolysis
- Strep. pyogenes growth is inhibited by bacitracin (zone of inhibition)
- Strep. agalactiae growth is not inhibited by bacitracin
Rheumatic fever (general)
- most serious sequaelae of Strep. pyogenes
- It follows 1-5 weeks after pharyngitis caused by group A beta haemolytic Streptococcus: Strep pyogenes
- children ages 5 to 15 years
- the most important cause of heart disease in young people in developing countries
- rare in the developed countries probably because streptococcal pharyngitis is treated promptly
- M types 1, 3, 5, 6, 18 were most frequently involved
- a marked tendency to be reactivated by recurrent streptococcal infections
- first attack of RF usually produces only slight cardiac damage, which, however, increases with each subsequent attack
- therefore important to protect from recurrent S. pyogenes infections by prophylactic penicillin administration
Pathogenesis of Rheumatic Fever
- Antibodies against group A Strep react with cardiac tissue
- Molecular mimicry: relationship between M protein of Strep pyogenes and myosin of cardiac tissue and protein in the joint and brain tissue
- Type II hypersensitvity (Antibody-mediated hypersensitivity)
- Systemic autoimmune reaction
Signs & symptoms of rheumatic fever
- fever, malaise
- Migratory nonsupurrative polyarthritis involves large joints: the knees, ankles, wrists & elbow
-
carditis - inflammation of all parts of the heart pancarditis (endocardium, myocardium, pericardium)
the major consequence with acute rheumatic carditis is chronic, progressive valvular disease. Mitral valve stenosis, incompetence leads to increased risk of infective endocarditis - thickened and deformed heart valves (mitral stenosis, mitral incompetence)
- may develop severe and progressive congestive heart failure
- Sydenham’s chorea: involuntary, uncoordinated movements and associated muscle weakness, often in prepubertal girls
- PANDAS: post streptococcal autoimmune neuropsychiatric disorders associated with streptococci)
- Erythema marginatum: rare characterisitc rash of acute rheumatic fever. It consists of erythematous, serpiginous, macular lesions with pale centres that are not pruritic. It occurs primarily on trunk & extremities
What is the criteria used to diagnose rheumatic fever
Jone’s criteria: >= 2 major criteria or 1 major + =>2 minor criteria
Major manifestations
1. carditis
2. polyarthritis
3. chorea
4. erythema marginatum
5. subcutaneous nodules
Minor manifestations
1. fever
2. arthralgia
3. previous rheumatic fever
4. raised ESR or CRP
5. Leucocytosis
6. first-degree AV block
- supporting evidence of preceding streptococcal infection: recent scarlet fever, raised antistreptolysin O or other streptococcal antibody titer, positive throat culture
What is the laboratory test for Rheumatic fever
ASO = antibody to streptolysin O
What are the prevention & control
- Detection and early antimicrobial therapy of respiratory and skin infections with group A streptococci
- Prompt eradication of streptococci from early infections effectively prevent the development of post-streptococcal disease (acute glomerulonephritis, rheumatic HD, arthritic, fever, carditis)
- maintenance of adequate penicillin levels in tissues for 10 days
- erythromycin is an alternative drug
- Antistreptococcal chemoprophylaxis in persons who have suffered an attack of rheumatic fever
- One injection of benzathine penicillin G intramuscularly every 3-4 weeks or daily oral penicillin
- chemoprophylaxis in such individuals, especially children, must be continued for years
What is endocarditis
infection of the valves of heart and endocardium
What is the predisposing factors / high risk of endocarditis
- patients with prior endocarditis
- patients with prosthetic heart valves
- congeital heart disease
- rheumatic heart disease
- intravenous drug user (IVDU)
- patients with indwelling intravenous catheter (IV)
entry of microorganisms of endocarditis
- at the site of dental surgery
- indwelling IV catheter / cannula
- IVDU
pathogenic mechanism of endocarditis
-
Endothelial damage due to
*turbulent blood flow around the valve (rheumatic heart disease, congeital heart disease)
*direct injury from foreign bodies (Intravenous catheters)
* repeated intravenous injections in intravenous drug users (IVDU) - colonization of microorganism on damaged endothelium & damaged valve
- adhesion of microorganisms by glycocalyx
- infection established
- vegetation formation by combination of microorganisms + thrombus - leads to valve destruction
Complications / sequelae of endocarditis
- valve destruction, valve regurgitation
- spread to myocardium and abscess formation
- conduction defect (AV block, sinus bradycardia)
- embolic phenomena (cerebrovascular accident - CVA, infarct in spleen, kidney, eye, septic pulmonary emboli)
- Ag-ab complex formation (Osler’s node, Roth spot)
Clinical features of endocarditis
depend on virulent of organisms & time course of illness
- acute endocarditis (days)
- subacute endocarditis (weeks to months)
- constitutional symptoms (fever, chills, night sweats, anorexia)
- consequences of destruction of heart valves and associated structures (new murmur, heart failure, atrioventricular AV block - PR prolongation)
-
embolic phenomena:
**Left-sides endocarditis **
- CVA or brain abscess
- splenic or renal infarcts
- splinter haemorrhages
- Janeway lesions - painless, erythematous, hearmorrhagic or pustular lesions
- retinal haemorrhages
- conjunctival haemorrhages
Right sided endocarditis
- septic pulmonary emboli (cough, shortness of breath, chest pain, haemoptysis)
4. antigen-antibody deposition from uncontrolled infection
- Osler’s nodes - painful
- Roth’s spot
- Glomerulonephritis (hematuria)
- arthritis
Pathogens of endocarditis
General: viridans streptococci of several species (S sanguinins, S salivarius, S mutans)
Native valve:
- community onset: viridans group streptococci, Staph. aureus, Strep. bovis, Enterococcus species
- health care associated: S aureus, Enterococcus species, Staph. epidermidis
- IVDU: S aurues, gram -ve rods (Pseudomonas, candida)
Prosthetic valve
- early: S epidermidis, S aureus
- late: S aurues, viridans group streptococci, enterococcus species, S epidermidis
Pacemaker or defibrillator: S epidermidis, S aureus
Culture negative: prior antibiotics, bartonella species, Coxiella burnetti, Brucella species, Tropheryma whipplei
Diagnosis of endocarditis
Modified Duke’s criteria
Definitive endocarditis: 2 major / 1 major + 3 minor / 5 minor
Possible endocarditis: 1 major + 1 minor / 3 minor
Major criteria
1. Possitive blood culture
* typical organism from 2 cultures
* persistent positive blood cultures taken > 12 hours apart
* 3 or more positive cultures taken over > 1 hour
2. Endocardial involvement
* positive enchocardiographic findings of vegetations
* new valvular regurgitation
Minor criteria
1. Predisposing valvular or cardiac abnormality
2. Intravenous drug misuse
3. Pyrexia >= 38 degree celcius
4. Embolic phenomena
5. Vasculitis phenomenon
6. Blood cultures suggestive: organism grown but not achieveing major criteria
7. suggestive echocardiographic findings
What is the criteria used for diagnosis of endocarditis
Modified Duke’s criteria
Definitive endocarditis: 2 major / 1 major + 3 minor / 5 minor
Possible endocarditis: 1 major + 1 minor / 3 minor
Major criteria
1. Possitive blood culture
* typical organism from 2 cultures
* persistent positive blood cultures taken > 12 hours apart
* 3 or more positive cultures taken over > 1 hour
2. Endocardial involvement
* positive enchocardiographic findings of vegetations
* new valvular regurgitation
Minor criteria
1. Predisposing valvular or cardiac abnormality
2. Intravenous drug misuse
3. Pyrexia >= 38 degree celcius
4. Embolic phenomena
5. Vasculitis phenomenon
6. Blood cultures suggestive: organism grown but not achieveing major criteria
7. suggestive echocardiographic findings
Diagnosis of endocarditis
- Blood cultures: 3 sets within 24 hours blood cultures should be obtained prior to administering antibiotics & antibiotic sensitivity test
- Some organisms difficult to grow - detect antibody in the blood
- Echocardiogram
- ECG (prolong PR interval)
How to differentiate between alpha-haemolysis
- Streptococcus pneumoniae is inhibited by Optochin
- Streptococcus viridans is not inhibited by optochin
Treatment for endocarditis
- without treatment, endocarditis is always fatal
1. antimicrobial therapy (bactericidal drugs)
2. vancomycin + ceftriaxone / gentamicin
3. specific antimicrobial therapy switched when the results of blood cultures and antibiotic susceptibility tests are known
4. 4 to 6 weeks of antimicrobial treatment
5. surgery (in some case)
What is myocarditis
Inflammation of the myocardium that result in injury to the cardiac myocytes (myocardial fibers)
What is the aetiology of myocarditis
Aetiology
1. infections: haematogenous spread / direct spread from adjacent tissue
- viruses: coxsackie, CMV, EBV, Influenza, Parvovirus B 19
- Bacteria: Corynebacterium diphtheriae, Borrelia (Lyme disease)
- protozoa: Trypanosoma cruzi (Chagas disease), toxoplasma gondii
- helminths: Trichenella spiralis, Visceral larva migrans
2. immune mediated
- post viral
- post streptococcus (rheumatic fever)
- drug sensitivity (methyl dopa, suphonamides, doxorubicin)
- systemic lupus erythematous (SLE)
- transplant rejections
3. others
- sarcoidosis
- giant cell myocarditis
- radiation
clinical features of myocarditis
- asymptomatic or self limited
- chest pain
- fever, constitutional symptoms
- heart failure
- arrythmias
Diagnosis of myocarditis
- ECG changes may be non specific
- Lab tests
- increase myocardial specific enzymes
- X ray - cardiomegaly, pulmonary congestion
- endomyocadial biopsy: showing lymphocytic infiltration with myocytic necrosis
Treatment for myocarditis
- supportive care, restrict physical activity
- treat CHF, treat arrhytmias
- anticoagulation
- treat underlying cause if possible
What are the causes of pericarditis
- infections
- autoimmune
- trauma
- malignancy
pathophysiology of pericarditis
- infection - haematogenous spread or direct spread from adjacent tissue
- inflammation of pericardium - pericardial effusion
- can lead to cardiac tamponade
Clinical features of pericarditis
- fever
- chest pain: worse on inspiration, coughing
- improve on sitting, leaning forward
- friction rub on auscultation
- heart failure
infective aetiological agent of pericarditis
- virus: coxsackie, echo, HIV, CMV
- Bacteria: Staph aureus, Strep pneumoniae, M tuberculosis
- Fungus: Histoplasma, coccidioides
Diagnosis and treatemnt of pericarditis
- culture and sensitivity of pericardial fluid
- cardiac enzymes
- ECG
- chest X ray, echocardiogram, cardiac MRI
Treatment
1. symptomatic
2. supportive
3. pericardiocentesis in cardiac tamponande
