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Sheep Infection Trials with 'Phase-Locked' Vpma Expression Variants of Mycoplasma agalactiae-Towards Elucidating the
Rohini Chopra-Dewasthaly1, Andreas Dagn1, Christian Lohinger1
1Institute of Microbiology, Department of Pathobiology, University of Veterinary Medicine Vienna, Veterinaerplatz 1, A-1210 Vienna, Austria.
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.
Insights
Mycoplasma agalactiae
Area of Science:
- Veterinary Microbiology
- Molecular Biology
- Infectious Diseases
Background:
- Mycoplasma species possess large multigene families responsible for surface protein variations.
- The Vpma family in Mycoplasma agalactiae is crucial for surface antigen variation, but the in vivo roles of all variants are unknown.
- Previous studies examined only two Vpma variants, leaving the infectivity of others uncharacterized.
Purpose of the Study:
- To investigate the in vivo infectivity and disease progression of all six Vpma expression variants of Mycoplasma agalactiae.
- To compare the pathogenicity of individual Vpma variants using isogenic phase-locked mutants (PLMs) in a natural host model.
- To determine if the inability to phase-lock Vpma expression affects Mycoplasma agalactiae's ability to initiate infection and cause mastitis.
Main Methods:
- Experimental intramammary infections in sheep using six distinct Mycoplasma agalactiae PLMs, each expressing a single Vpma variant.
- Infection models included a control wildtype strain (PG2) and thorough clinical, pathological, and bacteriological examinations.
- Assessment of milk quality, quantity, and somatic cell counts to evaluate disease impact.
Main Results:
- All six Vpma PLMs, except PLMU, successfully initiated intramammary infections and caused mastitis, indicating Vpma phase-locking is not essential for infection.
- PLMU exhibited a colonization and multiplication defect in the initial 24 hours post-infection.
- PLMV and PLMX demonstrated a higher potential for systemic spread compared to other variants.
Conclusions:
- The Vpma expression phase does not significantly impede Mycoplasma agalactiae's ability to initiate mastitis in sheep.
- Specific Vpma variants (PLMV, PLMX) may possess enhanced capabilities for systemic dissemination.
- This study provides the first comprehensive in vivo evaluation of all isogenic Vpma expression variants in Mycoplasma agalactiae within its natural host.
