Microbiology Test

Susceptibility testing, Fungi

Dr. Nithin Jayan
Medically Reviewed by Dr. Nithin Jayan, MBBS, DNB
Last Updated on Apr 29, 2014
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Test : 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.

Physiology : 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.

Interpretation : 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).

Susceptible (S) - Fungus is treatable for the suggested dose of the drug

Intermediate (I) - can, mostly, be reclassified as sensitive /resistant when retested

Resistant (R) - Infection not treatable, as the MIC of the tested drug exceeds safe levels

Sample : Fungal specimen

Test Method : Susceptibility testing

Related Tests : Blood fungus culture, fungus smear, sputum fungus culture.



References : +



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