Mycoplasma pneumoniae and its role as a human pathogen

Abstract

Mycoplasma pneumoniae is a unique bacterium that does not always receive the attention it merits considering the number of illnesses it causes and the degree of morbidity associated with it in both children and adults. Serious infections requiring hospitalization, while rare, occur in both adults and children and may involve multiple organ systems. The severity of disease appears to be related to the degree to which the host immune response reacts to the infection. Extrapulmonary complications involving all of the major organ systems can occur in association with M. pneumoniae infection as a result of direct invasion and/or autoimmune response. The extrapulmonary manifestations are sometimes of greater severity and clinical importance than the primary respiratory infection. Evidence for this organism's contributory role in chronic lung conditions such as asthma is accumulating. Effective management of M. pneumoniae infections can usually be achieved with macrolides, tetracyclines, or fluoroquinolones. As more is learned about the pathogenesis and immune response elicited by M. pneumoniae, improvement in methods for diagnosis and prevention of disease due to this organism may occur.

FIG. 1.

Phylogeny of mycoplasmas reconstructed from 16S rRNA sequence comparisons. Branch lengths are proportional to evolutionary distance (the number of base changes per 1,000 nucleotides). The scale at the bottom denotes the branch distance corresponding to five base changes per 100 nucleotides. Reprinted from reference with permission.

FIG. 2.

Spherical colonies of M. pneumoniae growing on SP4 agar. Magnification, ×95.

FIG. 3.

Proposed scheme for cell division and duplication of the terminal attachment structure in M. pneumoniae. Reprinted from reference with permission.

FIG. 4.

Scanning electron micrograph of M. pneumoniae cells. Whole mycoplasmas are shown, with terminal attachment structures indicated by arrowheads. Reprinted from reference with permission.

FIG. 5.

Transmission electron micrograph of M. pneumoniae-infected hamster tracheal ring, demonstrating the close association of the attachment structure to the epithelium (arrow). (Copyright J. L. Jordan and D. C. Krause.)

FIG. 6.

Data from an active surveillance study performed in Ohio in 1991, showing age-specific rates of community-acquired pneumonia due to the major bacterial pathogens. M. pneumoniae infections were diagnosed by seroconversion, using CF tests. These data demonstrate that M. pneumoniae causes a relatively large proportion of pneumonias of sufficient severity to warrant hospitalization among persons younger than 50 years but that it is also an important cause of pneumonia in older age groups. Sp, S. pneumoniae; Mp, M. pneumoniae; Lp, L. pneumophila; Cp, C. pneumoniae. Reprinted from reference with permission of the publisher.