NRMM – Results of the NRMM EQA distributions raise important issues!

During 2005 and 2006 two NRMM EQA shipments have been distributed and the results analysed. The results raise important issues!

The Nordic Reference Group on Methods in Medical Mycology (NRMM) is organised by the Nordic Society of Medical Mycology (NSMM), but the representatives are appointed by the respective national society of clinical microbiology or a corresponding national body. NSMM has representatives from Denmark, Finland, Iceland, Norway and Sweden.

The main tasks of NRMM are:

• to propose methods for species identification and antifungal susceptibility testing in Nordic clinical mycology

• to address antifungal resistance development in the Nordic countries

• to organise a scheme for external quality assessment for the Nordic medical microbiology laboratories

• to define suitable diagnostic levels in medical mycology for differently sized clinical laboratories

The NRMM will liaise and work closely with its European counterpart, the EUCAST AFST committee.

Antifungal susceptibility

The most important Candida species have a predictable susceptibility pattern to antifungal drugs:

Correct species identification will therefore give important information regarding antifungal susceptibility.

Antifungal susceptibility testing

Antifungal susceptibility testing has only recently become standardised and available in some specialised laboratories. One of the reasons for the slow development of standardised methods is that amphotericin B was the only antifungal drug available for many years and therefore also the only option for treatment of serious infections. Others have been difficulties in getting reproducible endpoints due to dependence of choice of media, temperature, inoculum sizes etc.

Two reference methods are currently available:

• MIC-determination according to the EUCAST
• MIC-determination according to the NCCLS (reference method)

Etest is commercially available alternative method which is useful for routine testing:

• MIC-determination with Etest

The above mentioned methods are all designed to determine the MIC of the microorganisms. The MIC is evaluated against a breakpoint. Breakpoints are found in the recommendations of breakpoint committees such as the NCCLS, EUCAST (under development) and NRMM (under development - see link in margin).

General aspects on susceptibility testing of yeasts

Susceptibility testing of yeasts should be performed in addition to species identification in the following situations:

• Yeast isolated from normally sterile sites (e.g. blood, biopsies, bowel-, joint- and spinal fluid, abscesses).

• Yeast isolated from sites with a normal flora should be tested if requested by the clinician or if the clinical information indicates a need for susceptibility testing (eg. ongoing antifungal treatment, therapy failure, long term treatment)

• Yeast isolated from patients with recurrent vaginal candidiasis treated with fluconazole

Aspects on resistance development in yeasts

Antimicrobial resistance in yeasts is an increasing problem. Inherent poor antimicrobial sensitivity is a clinical problem in certain Candida species. And some of these species cause opportunistic infections in compromised hosts. In other settings repeated use of azoles, may lead to high-level resistance even in normally susceptible species. Antimicrobial resistance in other fungi than yeasts is as yet inadequately investigated. 

Reference laboratories

Susceptibility testing might sometimes be problematic. “Difficult” strains, uncommon yeast species and moulds should be sent to one of the national reference laboratories.