Cryptococcus neoformans: pseudohyphal forms surviving culture with Acanthamoeba polyphaga

Abstract

During experiments on the gastrointestinal tract as a possible portal of entry for C. neoformans, the authors occasionally observed the free-living amoeba, A. polyphaga, growing in the presence of C. neoformans cultured from mouse feces. Examination of the amoebic trophozites revealed that they were engorged with yeast cells. Over a period of 2 to 3 weeks of incubation, the amoebae apparently killed most of the yeast cells. Some of the surviving C. neoformans cells formed atypical colonies which contained pseudohyphae. Seven other strains have since been cultured with this amoeba. Pseudohyphal forms were found among the surviving colonies in all strains tested. Virulence studies were performed on one randomly pseudohyphal isolate from each of the eight strains of C. neoformans. Pseudohyphal isolates from seven of the eight strains failed to kill mice 30 days after intracranial inoculation. The potential role of soil amoebae in the control of C. neoformans in nature is discussed.