Species Identification, Susceptibility and Resistance Invasive aspergillosis remains an infection that carries a high mortality. Despite the availability of new formulations and new potent antifungal agents, approximately 30 to 50% of patients die due to the infection. Treatment failure is mainly due to host related factors such as persistence of the underlying condition. However, the susceptibility of the infecting strain contributes to the success of therapy. Clinical microbiology testing results at present rarely contribute to clinical decisions in the management of patients with invasive aspergillosis. Identification of the strain to species level is of great importance, given the variable susceptibility of aspergillus species to different classes of antifungal agents. In the absence of positive cultures species identification can be achieved by molecular biological methods as oppossed to serology. The low sensitivity of culture precludes in vitro susceptibility testing in many cases due to the absence of a viable strain. Methods for in vitro susceptibility testing have been developed by the NCCLS and are in being developed by the EUCAST. In vitro susceptibility tesing has been shown to be reproducible and the MIC results correspond with clinical response for some of the azoles. However, several drawbacks need to be addressed including the turn-around time in the laboratory and validation of the methods for species other than A. fumigatus. Resistance, defined as high MICs, in A. fumigatus has been reported for the azoles including itraconazole, voriconazole, ravuconazole and posaconazole. In sporadic cases cross-resistance was observed. Although the incidence of resistance is low, early recognition of resistant strains is vital given the rapid progressive course of the infection. The demonstration that certain mutations correspond with phenotypic resistance might be usefull for early detection of resistance.
Full conference title:
43rd Interscience Conference on Antimicrobial Agents
- ICAAC 43rd