DEVELOPMENT OF A DIAGNOSTIC-TEST FOR MIKROCYTOS-ROUGHLEYI, THE ETIOLOGIC AGENT OF AUSTRALIAN WINTER MORTALITY OF THE COMMERCIAL ROCK OYSTER, SACCOSTREA-COMMERCIALIS (IREDALE AND ROUGHLEY)

Diagnosis and epidemiology of Mikrocytos roughleyi, the aetiological a gent of Australian winter mortality of the rock oyster, Saccostrea com mercialis (Iredale & Roughley), has been hampered by the small size of the pathogen and the low intensity of natural infections. Inoculation of experimental oysters with filtered, unpurified tissue homogenate f rom oysters infected naturally produced experimental infections after 22 weeks but hyperinfection was not successful. DNA was extracted from naturally infected, experimentally infected and uninfected oysters, t hen oligonucleotide primers were used in polymerase chain reactions to provide the basis for a molecular bioassay. One pair of primers produ ced am amplicon of 680 base pairs in length that was correlated direct ly to the presence of M. roughleyi in oyster tissues. The assay was ab le to detect a single organism of M. roughleyi in 400 host cells.