Studies on Mycoplasma ovipneumoniae in New Zealand sheep : epidemiology and comparison of isolates : a thesis presented in partial fulfilment of the requirements for the degree of Master of Science in Microbiology at Massey University, New Zealand

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Massey University
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As part of a larger study to examine the role of M. ovipneumoniae in chronic non-progressive pneumonia (CNP) of sheep, the colonisation of the respiratory tract by mycoplasmas was examined in two flocks of lambs over . a nine month period. In both farms M. ovipneumoniae was detected in the ewes at the time of first swabbing of the lambs. The two flocks of lambs differed in the time when the nasal cavity first became colonised by M. ovipneumoniae: thus in Flock 2 M. ovipneumoniae was detected in the nasal cavity relatively early and also became disseminated throughout the flock some months earlier than occurred in Flock 1. Nevertheless, M. ovipneumoniae was widespread in both flocks of lambs by March i.e. at• or before peak seasonal prevalence of CNP. At slaughter in May, Flock 2 (colonised early) had a much higher prevalence of CNP than Flock 1. These findings are consistant with the hypothesis that M. ovipneumoniae colonises the nasal tract of lambs and subsequently invades the lung possibly in response to the stress of exposure to hot dry weather. The second part of this thesis is concerned with the adaptation of Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) to distinguish strains of M. ovipneumoniae with the ultimate objective of comparing M. ovipneumoniae strains isolated from pneumonic lungs to nasal isolates and isolates from apparently normal lungs. Isolates from different sources were heterogeneous when examined by SDS-PAGE, but comparisons were made difficult because of the excessive number of protein bands. In response to this problem fractions of M. ovipneumoniae were examined. Membrane preparations conserved the unique protein bands which in principle allow discrimination between strains, but because the number of protein bands was still excessive we examined surface proteins by labelling intact cells with Fluorescein isothiocyanate (FITC). This approach still gave gels with too many protein bands for convenient comparisons to be made, but had the advantage of allowing the identification of surface proteins, some of which were unique to individual isolates. This encouraged us to combine SDS-PAGE with a classic immunological approach to strain identification i.e. we investigated the possibility of excising protein bands from gels for subsequent use as immunising antigens. One common protein band was excised, it was found to be antigenic and the antisera crossreacted with a single line of identity in gel precipititin tests with all the strains tested. While within the time limit available we have examined only one common protein band, the result suggests that the excision of individual strain-specific protein bands from SDS-PAGE for use as immunising antigens will provide strain-specific antisera which should allow the development of a simple approach to strain identification.
Mycoplasma ovipneumoniae, Sheep diseases, Pneumonia in sheep