Mycoplasma fermentans strain incognitus, an organism recently identifi
ed in tissues of patients with AIDS and in tissues of otherwise health
y adults with an acute fatal respiratory disease, was evaluated for cy
topathogenicity for tracheal tissue in vivo and in vitro. In this stud
y, the organism produced a chronic infection of the lower respiratory
tract in LEW rats following intranasal inoculation and induced both ci
liostasis and cytopathology in experimentally infected tracheal explan
ts from rats. The time of onset of ciliostasis, type of cytopathogenic
ity, and localization of organism in strain incognitus were different
from those in other strains of M. fermentans as well as other species
of mycoplasmas isolated from humans. The results strongly support, but
do not prove, that M. fermentans strain incognitus is an unusually in
vasive mycoplasma, as it was the only strain found within respiratory
epithelial cells both in vivo and in vitro. Detection of the organism
within the lamina propria also supported the organism's invasive poten
tial. Further study of both the in vivo and in vitro models should pro
vide insights into this potentially unique mycoplasma-host relationshi
p.