Respiratory disease in a colony of rats. II. Isolation ofMycoplasma pulmonisfrom the natural disease, and the experimental disease induced with a cloned culture of this organism

Abstract

SUMMARYMycoplasma pulmonis was isolated from the pneumonic lung of a rat. Two groups of mycoplasma-free rats were inoculated, one with a culture of the M. pulmonis strain which had been cloned four times (group A) and the other with a lung homogenate of the rat from which the strain had been isolated (group B). A third group (C) consisted of uninoculated control animals. Each group was kept in strict isolation and allowed to breed so that the progeny was naturally exposed to any pathogens present in the inoculated animals. After different periods of exposure, rats were autopsied, respiratory tracts and inner ears were cultured for mycoplasmas and bacteria, and sera were tested for complement-fixing antibodies to murine mycoplasmas.In group-A rats, M. pulmonis was consistently isolated from the inner ears or lungs from 50 to 715 days after exposure. Complement-fixing antibody to M. pulmonis was detected 20 days after inoculation, but in the naturally exposed progeny antibody took longer than 50 days to develop. Antibodies to the other known mycoplasmas of murine origin, M. arthritidis and M. neurolyticum, were never found. Purulent otitis interna was consistently found from day 55 onwards, while lung lesions were first observed at 85 days and persisted to 715 days. Pulmonary lesions developed more slowly in inoculated parents than in exposed progeny. Similar results were found in group-B rats, which were examined up to 441 days after inoculation. Uninoculated group-C rats were examined up to 768 days of age, but M. pulmonis was not recovered; of the 54 animals whose serum was tested all were negative to the three species of mycoplasmas, except one which had a titre of 16 with M. pulmonis. Pneumonia, bronchiectasis or lymphoreticular hyperplasia were not seen in any of these control rats. Bacterial respiratory pathogens were not isolated from rats in any of the groups, nor was antibody to Sendai virus detected.The results suggest that M. pulmonis alone can cause pneumonia and bronchiec-25 HYG 70P. WHITTLESTONE AND OTHERS tasis in rats since mechanical carry-over of another pathogen with the initial cloned inoculum is very unlikely and there was no evidence for the participation of any other rat pathogen. The respiratory disease induced by the cloned culture was comparable with that induced by the lung homogenate, and with the well-known syndrome of chronic respiratory disease and bronchiectasis in the rat.

Mycoplasmosis in Ferrets

“…The clinical signs and microscopic lesions in ferrets with the emerging respiratory disease described here closely resembled signs and lesions described for pigs infected with M. hyopneumoniae ( 34 ), rats infected with M. pulmonis ( 35 ), and cattle infected with M. bovis ( 36 ). For all of these species, chronic pulmonary mycoplasmosis is characterized by lymphoplasmacytic perivascular cuffing and extensive BALT hyperplasia, as was observed in ferrets in this study.…”

Protective effect of vaccination against Mycoplasma pulmonis respiratory disease in rats

“…There is sufficient reason to suspect that the development of MRM might be immunologically mediated. For example, the severity of MRM in both rats and mice appears to be directly proportional to the immune response; i.e., the animals with the most severe lesions have the highest complement-fixing antibody titers (15,31). In addition, the lesions both in mice infected with M. pulmonis and in hamsters infected with M. pneumoniae are lessened by suppression of cell-mediated immunity (9,26).…”

“…infection with greater than 105 colony-forming units of M. pulmonis (6). The disease in rats is chronic regardless of the infecting dose (6) and probably persists for the lifetime of the animals (31). The predominant lymphoid cells which infiltrate mouse lungs are plasma cells; in rats these are a minor component, and lymphocytes predominate (6).…”

Localization of <I>Mycoplasma pulmonis</I> in Mice

“…They were proved by etiological and serological checking [6,7] to be free from Salmonella spp., Pasteurella pneumotropica, Escherichia coli 0115a,c: K(B) [15,16] Isolates were subjected to a growth inhibition test using hyperimmune rabbit sera to strains 925T and PG-22 of M. pulmonis, strain PG-6 of M. [10,11,13,24] that M.…”

“…Although numerous reports [3] have been published on the isolation of the organisms from the respiratory system of rats and mice, distribution of the organisms in other sites of the hosts has not been extensively examined. In rats, isolation of the organisms from the nasopharynx [2,10], inner and middle ears [8,10,11,13,24] and female genital tract [8], as well as from the respiratory tract [3] has been described and Juhr [9] found that M. pulmonis were located in the epithelial cells of the urogenital, intestinal and respiratory tracts for a long time after mono-contamination of germf ree rats.…”