DNA RELATEDNESS BETWEEN FIELD ISOLATES OF MYCOPLASMA F38-GROUP, THE AGENT OF CONTAGIOUS CAPRINE PLEUROPNEUMONIA, AND STRAINS OF MYCOPLASMA-CAPRICOLUM

DNA-DNA hybridization experiments were carried out in order to clarify the taxonomic relationships between the F38 group of caprine mycoplas mas, the established etiologic agents of classical contagious caprine pleuropneumonia, and Mycoplasma capricolum, an organism associated wit h septicemia, arthritis, and mastitis in goats and sheep. The taxonomi c status of the F38 group has been uncertain, principally because of t he serological, genomic, and other properties which it shares with M. capricolum. Tritium-labeled DNAs from the M. capricolum type strain (C alifornia kid) and from prototype strain F38 were hybridized with unla beled DNAs from these two strains and from four other isolates belongi ng to each group. The results showed consistent DNA relatedness values of about 70% between the F38 and M. capricolum groups, compared with levels of relatedness of about 90 and 85%, respectively, for the strai ns within each group. In addition, the results of comparisons of these 10 strains in which growth inhibition and immunofluorescence tests we re used confirmed the previously reported serological relationships be tween the two groups and reinforced other observations concerning thei r shared genomic and cell membrane characteristics, indicating that th ere is a close taxonomic relationship. However, as the 70% DNA related ness values between the M. capricolum and F38 groups also indicate a d egree of genomic difference inconsistent with a relationship at the sp ecies level, we conclude that our findings support previous proposals for classification of the F38 group as a subspecies of M. capricolum. In view of the prospective diagnostic problems, particularly those ari sing from the serological similarities of two putative subspecies, we believe that further studies should be performed to define additional phenotypic and genotypic properties that would allow more rapid and sp ecific differentiation of the F38 group mycoplasmas.