Isolation of a Mycoplasma Capable of Producing Polyarthritis in Mice

Abstract

A mycoplasma capable of producing polyarthritis in mice has been isolated from the liver of a mouse suffering from Tyzzer disease. It was designated as strain OK.
(1) Biological properties of strain OK.
Strain OK could grow well at 37°C under aerobic conditions in a culture medium containing the components of the basal PPLO medium of Morton, Smith and Leberman (Difco PPLO agar, dehydrated) and supplemented with 20ml of pooled horse serum per deciliter and 10ml of a 25% extract of fresh baker's yeast per deciliter.
After ten days' incubation the largest colonies of organisms grown on the agar medium were 1mm in diameter. The colonies remained colorless and transparent for 3 to 5 days after the incubation. They turned to be yellowish white and turbid thereafter.
Microscopic examination revealed large bodies scattered in the colonies. Upon phase-microscopic examination of the organism, it was found that there were several fine granules linked together with filaments in a tangled string in each small transparent capsule.
The organism fermented dextrose, maltose, and dextrin, but it was inactive against galactose and lactose. When 48-hour cultures were tested, the reduction of methylene blue was rapid and complete.
The colonies did not adsorb sheep erythrocytes, but produced β-hemolysis against these cells within 2 days. They did not reduce 2, 3, 5-triphenyl-tetrazolium chloride (TTC) under aerobic conditions.
(2) Pathogenicity of strain OK.
Intravenous inoculation into mice with 3×10^7CFU/ml of strain OK suspension in saline caused purulent polyarthritis in 7 to 10 days, but all the mice survived throughout the observation period.
The pathogenicity of the strain remained unchanged even after 60 subcultures, i.e., 2 years after the strain was isolated. Neither intranasal nor intraperitoneal inoculation caused such polyarthritis. After intranasal inoculation of 10 mice with the strain, periauricular depilation was noticed in 7 mice and pneumonia in 3 mice. After intravenous inoculation of 31 mice with the strain, pneumonia was seen in 11 mice, periauricular dipilation in 3 mice, and liver abscess in 1 mouse.
(3) Histopathological findings on polyarthritis caused by strain OK in mice.
Acute purulent polyarthritis was produced in 8 mice of the ten intravenously inoculated with the strain.
(4) Identification of strain OK.
Strain OK was considered to be a mycoplasma from its biological properties. It has been found by growth inhibition tests and gel diffusion tests that strain OK is serologically identical with Mycoplasma pulmonis.
It was indicated, however, that strain OK was similar to M. pulmonis and M. neurolyticum in sugar fermentation and similar to M. neurolyticum in Mb reduction tests.
In conclusion, strain OK was different from M. pulmonis in the pathogenicity for mice, since it was found to cause polyarthritis.