M. pulmonis may disseminate widely throughout the host and therefore may alter the experimental results in numerous ways. M. pulmonis infection in mice is an invaluable model for the study of host defenses against respiratory mycoplasmas in vivo, including those of M. pneumoniae , an important worldwide cause of human death and disability. Natural infection of laboratory rats and mice could seriously impair research efforts investigating a variety of body systems, primarily the respiratory, reproductive, and immune systems. Streptococcus pneumoniae is a gram-positive diplococcus commonly found in laboratory rodent colonies. More than 80 strains, grouped by capsular type, have been reported.
Transmission is primarily via aerosol from infected humans.
The organism is considered a commensal under most conditions, although host strain susceptibility differences have been reported. Typically, a carrier state is established in the nasal passages and middle ears. Clinical signs are uncommon, although natural outbreaks of disease have been reported. When present, clinical signs are nonspecific and may include dyspnea, weight loss, hunched posture, and snuffling. Virulence is related to several bacterial components, most prominently pneumolysin, a multifunctional toxin with distinct cytolytic and complement-activating activities.