11. Lab diagnosis of fungal infections

what are fungi?

eukaryotic organisms, that are slow growing, heterotrophic and aerobic

what are some surface molecules of fungi that can help with diagnosis and treatment?

membrane → ergosterol

wall → chitin, glucan and mannan

how can we classify fungi?

based on:

• morphology

• lifestyle

• pathogenicity

• on the infections they cause

classification of fungi based on morphology?

yeast → unicellular

molds → filamentous

dimorphic fungi → mold which form in the environment and yeast forming in the body at 37 degrees

classification of fungi based on their lifestyle?

saprophytic → absorbing dissolved organic material

commensal → relation btw two organisms which benefit eachother w/o consequences

pathogens → agent of disease

classification of fungi based on their pathogenicity?

primary → can elicit infection in normal host

opportunisitic → can only elicit infection in immunocompromised host

classification of fungi based on infections they cause?

skin infections

• superficial mycoses

• cutaneous mycoses

• subcutaneous mycoses

endemic mycoses

• systemic mycoses

• e.g. aspergillos, pneumocystis pneumonia and cyptococcosis

what are the steps of laboratory diagnosis of fungi infections?

1. pre-analytical → collection, storage and transport

2. analytical

   • direct detection of fungal agents → microscopical ex. and antigen detection

   • culture

   • identification

   • serology

   • antimycotic sensitivity tests

sample collection of fungal infections of normally sterile sites?

aspirate specimen is better than swab

tissue should be taken from the middle and from the margin of the lesion

abscess → both aspirated pus and piece of abscess wall should be sent

sample collection of fungal infections of normally non-sterile sites?

prep of site → clean with 70% alcohol

skin scrapings → from inflamed margin of lesion with blunt scalpel or edge of glass slide or by sticky tape

hair → plucked from the root (10-12 pieces)

nails → nail clippings or deep scraping

storage and transportation of specimens?

storage

• from normally sterile site, deep tissue → room temp

• from superficial site → 4 degrees

transportation

• should be less than 2 hrs

wet moun smear procedure?

for skin scrapings, nail clippings, hair shafts, urine etc.

1. clear specimen with KOH

2. heat specimen for 20 min

3. if specimen contains keratin → +30 min incubation in room temp

4. detect with light microscope OR stain with KOH + calcoflour white and use fluorescent microscope

BD glucan test for fungi?

detects polysaccharide cell wall component of many fungi → candida + molds

recommeded with repeated testing

ELISA for fungi?

to check for invasive aspergillosis

galactomann test to detect cell wall antigen

serum or bronchoalveolar lavage

Latex agglutinantion test?

A serological test used to detect the presence of fungal antigens or antibodies in a patient's sample, often helpful in diagnosing infections caused by fungi such as cryptococcosis or candidiasis.

CSF or serum

molecular methods for identification of fungi?

PCR tests based on specific DNA detection

Pan-fungal PCR

T2Candida test → can detect 5 candida species