Dunedin-ID Flashcards
What is the mechanism of MRSA?
Modified penicillin-binding protein (altered target site of beta-lactam binding)
mecA gene encodes for PBP2a which has an altered terminal amino acid resulting in hugely reduced affinity for beta-lactam drug binding
Discuss PVL genes regarding community acquired MRSA and hospital-acquired MRSA
Community acquired MRSA- many carry PVL genes
hospital-associated MRSA: PVL expression less common
Define multi-resistant MRSA
Either two or more of the non-beta-lactam antibiotics e.g. erythro/clinda,* co- trim, genta, rifampicin, fusidic, mupirocin, tetracycline, chloramphenicol
Or ciprofloxacin (marker for the EMRSA-15)
What is PVL (Panto-valentine leucocidin)?
a pore-forming necrotising exotoxin that causes leucocyte destruction and tissue necrosis, with marked neutrophil activation and release of pro-inflammatory cytokines
seen in MRSA
Treatment of non-multi-resistant MRSA
Non-severe: cotrimoxazole, clindamycin, erythromycin, doxycycline, rifampicin, fusidic acid, gentamicin
linezolid
Severe: vancomycin, teicoplanin, daptomycin
What is a S/E of linezolid
reversible bone marrow depression with prolonged use
irreversible neuropathy
optic neuropathy
serotonin syndrome
What is the MOA of linezolid?
bacteriostatic, inhibits bacterial proteins synthesis, binds to both 30s and 50s ribosomal subunits
acts against gram +ve
What is the MOA of daptomycin
cyclic lipopeptide bactericidal antibiotic that causes depolarisation of the bacterial cell membrane
ineffective in respiratory tract infections due to inactivation by pulmonary surfactant
What are S/E of daptomycin?
myopathy, peripheral neuropathy, eosinophilic pneumonia
What is the MOA of tigecycline?
protein synthesis inhibitor, binding at the 30s ribosomal subunit
limited in UTIs
active against acinetobacter and stenotrophomonas
NOT active against pseudomonas, proteus, Providencia
not suitable for treatment of ventilator-associated pneumonia or CNS infections
high volume of distribution
How to treat enterococci?
penicillin, amoxicillin/ampicillin or vancomycin
inherently resistant to cephalosporins
What is the difference between E.faecalis and E.Faecium?
E.Faecalis –> more virulent, sensitive to penicillin/amoxicillin
E.Faecium –> less virulent, usually resistant to penicillin/amoxicillin
Vanc resistant
What is the MOA of vancomycin?
Inhibits synthesis of bacterial cell wall by binding to “D- alanyl-D-alanine terminus of the pentapeptide side-chain” preventing cross-linking.
active against gram POSITIVE bacteria, cant penetrate outer lipid membrane of gram negatives
What are S/E of vancomycin
Nephrotoxicity, ototoxicity, “Red Man” syndrome, neutropenia, thrombocytopenia, rash
What is teicoplanin?
glycopeptide antibiotic, similar to vancomycin but longer half life
How do you get vanc resistance?
D-Ala D-Ala –> D-Ala D-Lac
What gene clusters give rise of Vancomycin resistance?
What are VRE Treatment options?
penicillin/amoxicillin/ampicillin
teicoplanin- only for Van B/ Van C
linezolid
daptomycin +/- beta-lactam
tigecycline
ceftaroline
What is the mechanism of pneumococcal resistant to penicillin and cephalosporin?
alteration of penicillin-binding proteins (transpeptidase enzyme)
therefore clavulanic acid (e.g. augmentin) adds nothing
What is IV penicillin MIC break points?
Non-meningeal infections:
- susceptible: <0.06 mg/L
- resistant >2mg/L
Meningeal infection
- susceptible <0.06mg/L
- resistant: >0.06 mg/L
What is the mechanism of macrolide resistance for S.Pneumonia?
Macrolide resistance occurs via either mefA gene (efflux pump, low level resistance) or ermB gene (alteration of binding site, high level resistance)
What is the difference between gram +ve and gram-ve bacteria?
Gram +ve: 2 layer cell wall (thick peptidoglycan layer), cytoplasmic membrane
Gram -ve: three layer cell wall (outer membrane is outer lipid bilayer), cell wall (thin peptidoglycan layer), cytoplasmic membrane
What is the mechanisms of beta-lactam resistance
1) altered porins (only in gram -ve bacteria)
2) beta-lactamases (ampC, EBSL, CRE)
3) prevention of binding
4) efflux pumps
What is the mechanism of resistance for ESCHAPPM organisms?
AmpC Beta-lactamse genes which may be found on bacterial chromosomes or plasmids
resistant to cephalosporins (apart from cefepime)
How to treat ESCHAPPM organisms?
Carbapenems - empiric abx of choice
cefepine
possibly tazocin
note cefepime is still effective
What are extended spectrum beta-lactamases (ESBL) resistant to?
Most commonly found on e.coli and klebsiella
Treatment: carbapenem
outpatient ESBL UTI: nitrofurantoin (useful for lower UTI), ciprofloxacin, cotrimoxazole, gentamicin, fosfomycin
List some carbapenem-resistant enterobacteriaceae (CRE)
What is the treatment for CRE?
note in Australia mainly NDM rather than KPC
Colistin no longer first line but can be used. tigecycline not useful for bacteraemia
CRE urine: nitrofurantoin, cotrimoxazole, ciprofloxacin, fosfomycin, stat dose IM amino glycoside
What is avibactam and what is the mechanism of action?
avibactam is a second generation beta-lactamase inhibitor
normally beta-lactamase inhibitors bind to the beta-lactamase inhibitor and undergo hydrolysis
Avibactam binds to the beta-lactamase enzyme and inactivates it through a process of “reversible cyclisation”. it is released/regenerated to continue to inhibit other molecules.
Can inhibit Class A enzymes (ESBL, KPCs) and Class C (AmpC producers) and Class D (OXA-48)
No activity against the metal-beta lactamases (NDM, VIM, IMP)
What are the most common organisms in meningitis?
strep pneumoniae, neisseria meningitis, listeria with age>50
Risk factors for meningitis?
- Abnormal communication between nasopharynx and subarachnoid space due to trauma or anatomic abnormality
- Anatomic or functional asplenia or immunoglobulin deficiency are risk factors for infection from encapsulated organisms (Pneumococci, Meningococci)
- Complement deficiency
- Terminal complement inhibitory - Eculizumab (2000 fold risk)
- HIV
What is the difference between Kernig sign and Bruzinski sign
Kernig sign: inability to full knee flexion when hip flexed
to 90 degree angle
Brudzinski: spontaneous flexion of hips during passive flexion of the neck
What are the indications for CT prior to LP?
Interpretation of CSF
HSV meningits- CSF often has many red cells
mollaret’s recurrent meningitis usually associated with HSV-2
What is the empiric treatment of bacterial meningitis?
- Dex 10mg IV q6hrly (maximum 4 days)
- ceftriaxone 2g IV BD
If pneumococcal risk, add IV vancomycin e.g. gram +ve cocci on initial stain, pneumococcal antigen +ve, suspected otitis, sinusitis, or mastoiditis
If listeria risk, add benpen 2.4g IV q4hrly
Dex helps with s.pneumonia, h.influenza (hearing loss)
What is streptococcal Suis associated with?
common cause of meningitis in SE Asia. Hearing loss +++. Associated with pigs & handling pork
Describe LP findings of aseptic meningitis and causes
CSF: lymphocyte-predominant pleocytosis, typically <500cells/uL, normal glucose concentration, normal or slightly elevated protein, negative bacterial antigen tests/ culture
Describe LP findings fo TB meningitis
*Predominant lymphocytic CSF >50%, with low CSF:blood glucose ratio (<0.5) and a high protein conc. >1.0 g/L
- Low numbers of bacilli in CSF - yield of ZN staining & culture adequate only if large volume of CSF is examined (>5 ml)
What sort of meningitis is common in HIV? particularly CD4 <100
cryptococcal meningitis:
Two species: Cryptococcus neoformans (immunocompromised) and Cryptococcus gattii* (immuno-competent)
May be associated with cerebral mass lesion e.g. cryptococcoma.
typically raised ICP
no role of steroids
What is the most common valvular lesion associated with IE?
mitral valve prolapse with regurg
previously was mitral stenosis secondary to RHD
What is a determinant of IE caused by streptococci?
the amount of dextran produced
What is the other name with streptococcus gallotyicus?
AKA strep bovis
associated with colon pathology such as cancer
What are HACEK organisms?
Oral gram negative bacilli that are slow to grow in traditional culture media
What are examples of culture-negative endocarditis?
*Bartonella
* Coxiella burnetii (Q fever)
* Brucella
* Legionella
* Tropheryma whipplei
What is empiric therapy for IE?
Native valve:
Benpen + fluclox + gent IV daily
OR
gent IV daily + vanc
Prosthetic valve:
Fluclox + vanc + gent
OR
Vanc + Gent
How to treat streptococcal IE specific therapy?
Depends on penicillin MIC
How to treat enterococcal IE?
What are some oral options for Infective endocarditis?
Many thing, but can trial linezolid + rifampicin
What are indications for surgery in infective endocarditis?
Heart failure
Uncontrolled infection (root abscess, persisting fevers and positive blood cultures despite >10d therapy, fungal or MDRO)
Prevention of embolism (Vege >15mm, large vege _ embolic episodes)
When to use prophylaxis for infective endocarditis?
high risk cardiac condition (prosthetic heart valve, rheumatic valvular heart disease, previous endocarditis, unrepaired cyanotic congenital heart disease)
PLUS
high risk procedure (dental procedure, tonsillectomy or adeniodectomy, surgery at site of an established infection)
What is the IE prophylaxis?
What is the CURB-65 score?
When can you use steroids with pneumonia?
What is Multi-drug resistant tuberculosis?
TB resistant to isoniazid and rifampicin.
note isolated rifampicin every rare, usually indicated MDR
What are risk factors for MDR TB?
- migrants from high risk areas such as china, Eastern Europe, India, PNG, Russia, SEAsia, sub-saharan and south africa
patients who treatment previously failed
failure to response to treatment within 2-3 months
contacts of MDR TB cases
What are CXR findings in HIV and TB?
CXR findings commonly less typical – may be lower zone, diffuse infiltrate, cavitation unusual, and less mediastinal adenopathy
Describe TB therapy:
Initiation phase: 2 months
- isoniazid, rifampicin, pyrazinamide, ethambutol
Continuation phase: 4 months
- isoniazid, rifampicin
usually total of 6 months but can extend to 9 months if cavitary disease, pulmonary TB still positive at 2 months, bone or joint ,TB meningitis
Is Q.gold affected by BCG vaccine?
NO
unlike mantoux test
What are treatment regimens for latent TB?
Isoniazid 300mg PO daily x 6 – 9 months
Isoniazid 300mg/Rifampicin 600mg daily x 3 months
Rifampicin 600mg PO daily x 4 months
Rifapentine 900mg + Isoniazid 900mg weekly x 12 weeks
Why is oral doxycycline 100mg BD the recommended first-line treatment option for chlamydia urogenital infection in non-pregnant females?
increasing neisseria gonorrhoea and mycoplasma genitalum azithromycin-resistance
Compared to standard pyogenic infection, mycobacterial bone and joint infections are typified by?
subacute presentation
Regarding HSV encephalitis, describe MRI findings
Unilateral temporal lobe involvement on MRI is more common than bilateral involvement
HSV1 is most common cause
HSV meningitis can be self limiting but NOT HSV encephalitis.
Regarding pregnancy and varicella exposure in someone without previous vaccination and no detectable serum VZV IgG
- should offer varicella-zoster immunoglobulin up to 10 days after exposure (BUT HAS TO BE BEFORE THE RASH)
- if she develops chickenpox, she has 10% risk of developing varicella pneumonia
In the treatment of a severe, complex intra-abdominal infection, metronidazole should be combined with which abx?
Cefepime
Prosthetic joint infections are often treated with surgery + rifampicin. Why?
anti-biofilm activity