Cryptococcus neoformans: size range of infectious particles from aerosolized soil

Abstract

Although cryptococcosis is characterized as a chronic central nervous system disease, it is generally accepted that the lungs are the primary portal of entry for the etiological agent. Despite this, there is a distinct lack of evidence that viable airborne particles of Cryptococcus neoformans are small enough to reach the alveoli. Two encapsulated strains and one nonencapsulated strain of C. neoformans were inoculated into 250-g quantities of sterile soil. Throughout the 0 to 12 weeks of incubation, this soil was aerosolized in a sealed chamber with a Waring blender. Samples of the resultant dust cloud were taken with an Anderson air sampler from which the numbers and sizes of viable airborne particles were determined. Of the viable organisms aspirated into the air sampler, 15% were 0.65 to 2 micron in diameter. As incubation time in soil increased, the size of the particles decreased, and increased numbers of C. neoformans cells 0.65 to 2 micron in diameter were isolated. The presence of viable cells less than 2 micron in soil aerosols indicated that, under certain conditions in nature, C. neoformans cells exist in sizes that are capable of deep lung deposition.