Derrick Edward Award Lecture. The pathogenic potential of mycoplasmas: Mycoplasma pulmonis as a model.

For years the ubiquity of Mycoplasma pulmonis in rodents overshadowed its pathogenic potential. Its etiologic significance in murine chronic respiratory disease was established only by recognition of the delicate equilibrium between organism and host. Environmental factors and genetic predisposition of the host rather than microbial virulence are the critical determinants of disease. The prevalence of M. pulmonis is undoubtedly related to the recently demonstrated in utero transmission and the ability of the organism to colonize and produce disease in the genital tract. The etiologic significance of Ureaplasma urealyticum in human genitourinary disease, like its murine counterpart, has been surrounded by controversy. Recent studies indicate that only a subgroup of colonized individuals develop clinical manifestations of disease, ranging from infertility to fetal wastage. While the natural occurrence of both respiratory and genital mycoplasmoses seriously restricts the usefulness of rats and mice for other research purposes, they represent useful models fo the study of human disease. The recognized morphologic similarities and similar natural histories of chronic bronchitis, bronchiectasis, and emphysema in humans and of M. pulmonis respiratory disease in rats and mice make the latter a particularly useful model for study of the pathogenesis of chronic pulmonary inflammation. At the same time, murine genital mycoplasmosis represents one of the few naturally occurring genital tract diseases in laboratory animals and therefore makes an attractive model for elucidating those subtle host-parasite interactions that predispose to genital disease and subsequent reproductive failure.