Effect of Media Modified To Mimic Cystic Fibrosis Sputum on the Susceptibility of Aspergillus fumigatus, and the Frequency of Resistance at One Center

Studies of cystic fibrosis (CF) patient exacerbations attributed to Pseudomonas aeruginosa infection have indicated a lack of correlation of outcome with in vitro susceptibility results. One explanation is that the media used for testing do not mimic the airway milieu, resulting in incorrect conclusions. Therefore, media have been devised to mimic CF sputum. Aspergillus fumigatus is the leading fungal pathogen in CF, and susceptibility testing is also used to decide therapeutic choices. We assessed whether media designed to mimic CF sputa would give different fungal susceptibility results than those of classical methods, assaying voriconazole, the most utilized anti-Aspergillus drug in this setting, and 30 CF Aspergillus isolates. The frequency of marked resistance (defined as an MIC of >4 mu g/ml) in our CF unit by classical methods is 7%. Studies performed with classical methods and with digested sputum medium, synthetic sputum medium, and artificial sputum medium revealed prominent differences in Aspergillus susceptibility results, as well as growth rate, with each medium. Clinical correlative studies are required to determine which results are most useful in predicting outcome. Comparison of MICs with non-CF isolates also indicated the CF isolates were generally more resistant.