Development of a diagnostic test for Mikrocytos roughleyi, the aetiological agent of Australian winter mortality of the commercial rock oyster, Saccostrea commercialis (Iredale & Roughley)

Diagnosis and epidemiology of Mikrocytos roughleyi, the aetiological agent of Australian winter mortality of the rock oyster, Saccostrea commercialis (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 from 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, then oligonucleotide primers were used in polymerase chain reactions to provide the basis for a molecular bioassay. One pair of primers produced am amplicon of 680 base pairs in length that was correlated directly to the presence of M. roughleyi in oyster tissues. The assay was able to detect a single organism of M. roughleyi in 400 host cells.