ABSTRACT
The significance of large multigene families causing high-frequency surface variations in mycoplasmas is not well-understood. Previously, VpmaY and VpmaU clonal variants of the Vpma family of lipoproteins of M. agalactiae were compared via experimental sheep infections using the two corresponding 'Phase-Locked Mutants'. However, nothing is known about the infectivity of the remaining four Vpma expression variants VpmaX, VpmaW, VpmaZ and VpmaV as they were never evaluated in vivo. Here, in vivo infection and disease progression of all six Vpma expressers constituting the Vpma family of type strain PG2 were compared using the corresponding xer1-disrupted PLMs expressing single well-characterized Vpmas. Each of the six PLMs were separately evaluated using the intramammary sheep infection model along with the control phase-variable wildtype strain PG2. Thorough bacteriological, pathological and clinical examinations were performed, including assessment of milk quality, quantity and somatic cell counts. Altogether, the results indicated that the inability to vary the Vpma expression phase does not hamper the initiation of infection leading to mastitis for all six PLMs, except for PLMU, which showed a defect in host colonization and multiplication for the first 24 h p.i. and pathological/bacteriological analysis indicated a higher potential for systemic spread for PLMV and PLMX. This is the first study in which all isogenic expression variants of a large mycoplasma multigene family are tested in the natural host.
ABSTRACT
Mycoplasma (M.) bovis was identified and reported in Austria as agent of infection and disease in cattle only once, namely in 2005 associated with a case of mastitis in a smallholding, but in 2007 it unexpectedly emerged as the cause of a devastating disease outbreak in a dairy herd of 100 individuals and spill over infection to pigs, both kept on the same mountain pasture. In 2008, M. bovis remained endemic at a low level in this region followed by the re-emergence of the agent in 2009 and a dramatic spread of the disease to further Alpine areas and their foothills in 2010 and 2011. From these outbreaks, a total of 94 M. bovis isolates including 7 porcine isolates were selected for genotyping. Two molecular tools, randomly amplified polymorphic DNA (RAPD) analysis and multi-locus variable number of tandem-repeat analysis (MLVA) were chosen to identify strain types involved in these outbreaks and to trace routes of infection and dynamics of dissemination. With both typing methods, the majority of Alpine isolates (96.8%) recovered over time from different areas and hosts was clustered into one group exhibiting a unique and indistinguishable profile which significantly differed from those of geographically unrelated strains including the type strain PG45 and 3 Alpine isolates which suddenly appeared and disappeared in 2009. Stability of the unique profile strongly indicated that a single M. bovis strain initiated the outbreak in 2007, crossed the host species barrier by infecting pigs, re-emerged in 2009 and became widespread in the Austrian Alps in 2010 and 2011. The remarkable dissemination and persistence of a single and unique M. bovis strain may reflect peculiarities of dairy management practices in the Alps based on Alpine transhumance and cooperative use of mountain pastures. As the source of the outbreak strain remains unknown, the findings of this study underscore the importance of continuous surveillance by monitoring further spread and persistence of M. bovis infections for effective control to minimize losses in Alpine dairy farming.
