Normally saprobic cryptococci isolated from Cryptococcus neoformans infections

We report two cases in which Cryptococcus laurentii was isolated from surgically resected pulmonary lesions but the cryptococcal cells in tissue reacted positively with a specific fluorescent antibody (FA) conjugate for Cryptococcus neoformans. Both patients had no apparent host defense defects. In both cases, multiple cryptococcal isolates were obtained from tissue, and yeastlike cells consistent with C. neoformans were seen in direct histology. The isolates were identified by assimilation patterns and standard procedures including phenoloxidase reactions. Since C. laurentii was consistently isolated by using stringent procedures, it was considered unlikely that the fungus represented surgical or laboratory contamination. Its presence may be the result of dual infection not detected by FA, but other possible explanations exist. The results show the value of the FA test in diagnostic mycology and call into question previous reports of cryptococci other than C. neoformans as agents of infection.