A comparative study of some cultural methods in the isolation of avian mycoplasma from field material.
Comparison was made between direct plating onto mycoplasma agar and culture in overlay or broth in the recovery of mycoplasma from avian field material from poultry, wild and exotic birds. The value of an atmosphere of increased carbon dioxide, provided by 5% carbon dioxide in nitrogen or by 'candle jar', and of 'restreaking', was also investigated. From a total of 1784 tissues examined in four experiments mycoplasma were recovered from 463 involving 509 strains. Of these strains, 73% were grown by direct plating, 82% by a combination of subcultures from overlay and fewer by the individual overlay subcultures. A proportion of recoveries was made by each method alone. Recovery of mycoplasma through culture in broth was markedly inferior to either direct plating or overlay culture. There was no apparent advantage in incubating mycoplasma plates in an atmosphere of increased carbon dioxide. Restreaking increased recoveries by only a small number. The mycoplasma recovered included the following recognised avian species or serotypes:- M. gallisepticum, M. gallinarum, serotype D, M. iners, sero-type F, M. meleagridis, serotype I, M. synoviae, M. anatis, A. laidlawii, and a number of untyped strains especially from exotic birds. Combinations of two or more serotypes were also isolated from approximately 10% of the tissues from domestic poultry. Although most serotypes were isolated by both direct plating and overlay methods, the recovery of serotype I and M. meleagridis seemed to be favoured by direct plating while M. gallisepticum and a number of untyped organisms were more frequently isolated after culture in overlay. The only organism recovered by one method alone was serotype D (from overlay) but only three recoveries were made. In the examination of avian tissue using conventional media it would seem that for maximum recovery of mycoplasma direct plating together with subcultures from overlay could be recommended. Incubation of plates in additional carbon dioxide seems unnecessary and 'restreaking' is of limited value.
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Sub-Department of Avian Medicine, University of Liverpool 'Leahurst', Neston, Wirral, England.
Jordan
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