Diagnosis and Manaement of Fungal Infections Flashcards
What can predispose to invasive mould infections
Immunocompromised High dose corticosteroids Trauma, Diabetes, COPD Haem malignancy bone marrow transpant HIV Organ translplant Malignancies
What can predispose to candidaemia
Immunocompromised High dose corticosteroids Abdo surgery, IV lines, Antibitoics, Diabetes, Lymphoma, Pregnancy Haem malignancy bone marrow transpant HIV Organ translplant Malignancies
Use of X ray in fungal diagnsois
Useful at giving hints but rearey diagnostic
GIve the Radiological signs of aspergillosis
CXR –> patchy changes. May see crecent -shaped lesions on a chest radiograph but this is a late sign following neutrophil recovery
CT –> Halo sign (early finding 1-10 days)
BUT AGAIN these are not diangostic only suspeicion
Diangosic methods
1) Direct microscopy
2) Culture ID Susceptbility
What is direct microscopy particularly good for
Can identify if fungus is present very quickly
But many cases where levels sare too small for funsu BUT hyphae may give clue about properties –> i.e. if its mucoraceous –> start antifungals immediately!!!!
What is the exception to fungi generally growing slowly
Candida will generalyl grow well witin 24 hours!
What can we use to culture yeasr
Chromagenic agar –> can hepl particualry for Candida
1) Dalmau culture
Firstly try to seperate C. ablicans –> if germ tubes present it is likely this
Then do biochemical tests –> test with assimilation studies
What can we use to identify mould culture
Generaly colous, morpholohical geatures and sporing upon microscopy can give us lots of information on diagnosis on culture alone and this is often clinically sufficient
What moudls are bad at being identified onculture
Agents of dark grey mycetoma –> these are often poor at sporing and form dark grey coloies –> under micscioe can only see huphae and hese samples need DNA identification tools
What Traditional sequencing method is a slow process for yeasts
Pyrosequencing –> used to give yeast ID in half a day
But MALDI-TOF Has superceded this
How does pyrosequecning work
Involved 4 enzymes and bases wer eindividually ingested
If base was incorprated it release a pyrophosphate which then gets converted to ATP
This drives a luciferase reaction producing a volt of light
The next base in then injjected
This conitinues until sequencing is complete
Quick but was limited to small gragments
What is MALDI-TOF
Matrix Associated Laser Desorption/Ionizaton - Time of FLight
It is a mass spectromoter –> initially almost too sensitive to give useful results but the MALDI-TOF matric means particles that are analysed and larger and the profile given realtes more to the organism and not where its grown.
It is much quicker and can be done in an hour but it very explensive
What do we used to test susceptibility of fungi
CLSI Borth dilution –> make diltions of antigungal agent and expose to suspencion of fungus to it
What serological methods can we use for fungal diagnosis
1) Examinaning Antiboides
2) examining antigens
Problem with examining anitboides
Can only be used if patients can mount an antibodyt response
I.e. look for antigen-antibody complexes from the patient serum
Also levels of normal funcus in lungs can vary i.e CF patients have hihgh levels that may still be normal
ALso false _ve reactions and false -ve reactions
What does examining antiboides work well in
Aspergilloma
Endocarditis
How do we examine antigents
Use mAB to target antigents
I.e. latex agglutination good for cryptococcus (latex with Ab to cryptococcus capsule)
ELisa board system targets cell wall antigens for aspergillus and candida –> i.e. against mannans and galactomannans
Fungitell Test
What is the Fungitell test
Uses the horseshoe coagulation cacade and this targets anything with beta-glucans in it
however need to extract blood from the crabs and no synthetic optoin is available yet
What are the probelms with elisa antigen tests
Lack of sensitivity - false negatives
this could be due to low levels of circulating mannan.galactommannan –> can get galactomannana in foods and there are limited periods of antigenamiea
How can we molecular ID Fungus
DNA PCR
What do we use as the target in PCR for fungi
Ribosomal rRNA as this can be specific and there are multiple copies
Why is PCR not the definitive test for invasive fungal infectiotns
1) Many choices of sample
2) Many method of DNA extraction
3) Contamination –> particlarly aspergillus as envionmental
THERE IS NO STANDARDISATION OF METHOD –> whilst the UK Fungal Consensus group tried to give standardisation this didnt work
How many PCR results are considered a positive result
2 +ve
BUT gnerally do PCR and antigen test!
What are the critical factors for succesful treatment of invasvie fungal infection
Prompt recognition of teratment
Aggressive antifungal treatment
Surgical resection of lesions
Reveral of immunosuppression –> the best way to treat fungal infections and more effective than any antifungals
What are the four management strategies for invasive fungal infections
Prophylaxis
Empirical Treatment
Defiinitve Treamtnet
maintenance treatment
Reasons for therapteutic failure to antifungals
Poor treatment compliance
Inadequeate drug absoprtion or dsitribtion
Drug interaction of inactivation
Drug resistance
