Mycoplasma leachii strain PG50 shows reduced adherence and invasion compared to M. bovis strains 428E and PG45.

Mycoplasma leachii is a member of the "Mycoplasma mycoides cluster", which includes the causative agent of contagious bovine pleuropneumonia (Mycoplasma mycoides subsp. mycoides). Mycoplasma leachii has been associated with severe outbreaks of polyarthritis, mastitis, and abortion in dairy cattle in Australia, Argentina, and China. As M. leachii has veterinary implications and is related to other foreign animal diseases of economic importance, we sought to investigate differences in adherence to and invasion of different bovine cells between M. leachii type strain PG50 and M. bovis strains (type strain PG45 and field strain 428E). Specifically, we tested the strains with Madin-Darby bovine kidney (MDBK), bovine turbinate (BTu), and the carticular progenitor 5 (CP5) cells for 2 and 24 h. Additionally, we tested the MDBK and BTu cells with both non-cytopathic bovine viral diarrhea virus (BVDV-1b) positive and BVDV negative fetal bovine serum. Mycoplasma leachii strain PG50 adhered and invaded less efficiently than M. bovis strains 428E and PG45 with a log₁₀ reduction in adherence and invasion ranging from 1.5 to 2.9 CFU/mL. The reduced adherence and invasion of M. leachii type strain PG50 was observed regardless of the incubation time (2 h vs. 24 h), tested cells (MDBK, BTu, or CP5), cell type (epithelial or fibroblast), or presence of BVDV. Future work should further characterize M. leachii to further assess its risk to animal health and compare it phenotypically to other members of the M. mycoides cluster.