Epidemiology and clinical importance of in vitro resistance in fungi

J. L. Rodriguez Tudela

Author address: 

Servicio de Micologí­a, Centro Nacional de Microbiologí­a, Instituto de Salud Carlos III, Majadahonda, Espagna


Since 1997, there are available standardized methodologies for detecting antifungal resistance of human pathogenic fungi. CLSI was the first organization devoted to create antifungal susceptibility standards. Thus, two standards, for yeasts and for filamentous fungi can be used for establishing the susceptibility or resistance to antifungal drugs. Later, but with great enthusiasm, Antifungal Susceptibility Testing Subcommittee of European Committee on Antibiotic Susceptibility Testing has produced their own European Standards. One of them that dedicated to detect the resistance to antifungals in yeasts able to ferment glucose, is already available (Edis 7.1). In addition, the standard devoted to detect the resistance to antifungals in Aspergillus is in the final phase. With those tools, many epidemiological studies have been performed in order to ascertain the rate of resistance for antifungals of clinical use in human fungal pathogens. The most important and valuable studies are those based in population active surveillance. However, for low incidence fungal infections, active surveillance is complex because many centers need to be involved together with a long period of study. In those cases, data obtained from passive surveillance are, frequently, the only available. The data obtained from these studies identify those strains, species or genera that have high MICs to antifungal drugs. The comparison, in time, of surveillance studies indicate if species are developing secondary resistance or maintain the primary susceptibility pattern. In a broad sense, the data obtained from the studies is very important because identify species with intrinsic resistance to antifungals and also the species that have a tendency to develop secondary resistance. In addition, if the study is population based, the data reflects risk factors and the real rate of resistance and therefore public health interventions can be delineated and promoted. Lastly, the isolates showing high MICs can be analysed in order to identify mechanism of resistance in comparison with those strains with low MICs. The last phase, and very important, is to identify the clinical value of resistant strains. In other words, if the results obtained with antifungal susceptibility testing could predict the outcome of fungal infections. The answer is not easy; MIC value is a variable that need to be in context and the circumstances in fungal infections are very complicated to have a simple solution. However, there are many data in the literature showing that microorganisms with high MICs are more related with clinical failures than those with low MICs (the outstanding 9060 rule).

abstract No: 


Full conference title: 

2nd Trends in Medical Mycology
    • TIMM 2nd (2010)