A review of the morphological and biochemical features of the attachment process in infections with Mycoplasma pneumoniae.

Mycoplasma pneumoniae must attach to respiratory tract cells to cause primary atypical pneumoniae. The attachment process involves a receptor site on the external membrane surface of the host cell and a specialized attachment tip on the mycoplasmal cells. Attachment to lung fibroblasts and ciliated tracheal explants is time dependent, with maxima reached in 45-90 min at 37 C. Attachment to ciliated cells is slower, apparently because of continuous ciliary motion. Normally, less than 10% of available mycoplasmas become cell associated in vitro, perhaps because the pathogen must be in a particular growth phase or because only a small fraction of the M. pneumoniae population has complete or effective attachment tips. Mycoplasmas that attach to host cells normally have the constricted attachment tip oriented toward the host cell surface. Mycoplasmas are oriented vertically in cultures of densely ciliated cells, but can lie horizontally alone--and in close apposition to--cell membranes of sparsely ciliated or nonciliated cells. The site to which M. pneumoniae attaches, a sialoglycoprotein, is readily inactivated by neuraminidase, partially sensitive to pronase, and resistant to trypsin. Purified glycoprotein extracts bind to M. pneumoniae.