Susceptibility testing, Fungi Indications :
The invitro susceptibility testing for fungi is ordered for the following reasons:
Analyze the effect of anti fungal medications and to determine its impact on the fungi
Predict the clinical response or prognosis of a fungal infection after being subjected to specific antifungal therapy
A pure isolate of the fungus
is required for the test. The container with sample, and specific growth media, must display the identification of the isolate. It is then placed in a biohazard bag and sealed before being taken to a laboratory. If the sample cannot reach the lab immediately, it has to be stored at 28 degrees.
The fungus susceptibility test is carried out using the method of broth microdilution assay. An optimum medium which prevents drug- media interaction is selected. 1 ml of inoculate is incubated with the selected drug at 35 degrees C for a period of 2-3 days. The test takes between 5-7 days for completion.
Susceptibility testing for fungi
has become a necessity due to an increase in the number of invasive infections. The rise of antifungal resistance
as a significant clinical problem is another factor that makes this test mandatory.
Also, there are several established and novel antifungal medications in the market that are being put to use in multiple ways. Susceptibility testing helps to improve and maximize the therapeutic use of these agents besides helping in the development of newer and better drugs.
The lowest dilution showing nil visible growth is considered the ‘end point’ and this is compared to the end point in drug-free control tubes. For some drugs like azoles and 5-fluorocytosine, the end point is a 50% reduction in fungal growth.
The minimum inhibitory concentration (MIC) of the drug, which is the lowest concentration that prevents the visible growth of micro organism after overnight incubation, is determined.
Results may be reported as susceptible (S), Intermediate (I), or Resistant (R).
- Fungus is treatable for the suggested dose of the drug
- can, mostly, be reclassified as sensitive /resistant when retested
- Infection not treatable, as the MIC of the tested drug exceeds safe levels Sample :
Test Method :
Susceptibility testingRelated Tests :
Blood fungus culture, fungus smear, sputum fungus culture.