Investigation into recent declines in striped bass health in the Chesapeake Bay in Maryland resulted in the isolation of a putative new species of Mycobacterium. This isolate was obtained from fish showing skin ulcers and internal granulomas in various organs. The isolate was slow growing at 28°C; was nonchromogenic; showed no activities of nitrate reduction, catalase activity, Tween 80 hydrolysis, tellurite reduction, or arylsulfatase reduction; grew best at low salt concentrations; and was urease and pyrazinamidase positive. By PCR a unique insertional sequence was identified which matched nothing in any database. Analysis of the nearly complete 16S rRNA gene sequence also indicated a unique sequence which had 87.7% sequence homology to Mycobacterium ulcerans, 87.6% homology to Mycobacterium tuberculosis, and 85.9% homology to Mycobacterium marinum. Phylogenetic analysis placed the organism close to the tuberculosis complex. These data support the conclusion that the isolate probably represents a new mycobacterial species.

A nested polymerase chain reaction (PCR) was developed for detection of the microsporidian parasite Enterocytozoon saln~onis in blolog~cal samples (blood buffy-coat cells, feces, tissues, lymphocyte cultures) of chinook salmon Oncorhynchus tshaulj/tscha. A major second-round PCR product of 407 bp was readily identifiable in ethidium bromide-stained agarose minigels An internal probe was used to verify the identity of the amplified product by non-radioactive (digoxigeninbased) Southern blotting; final confirmation was made by DNA sequence analys~s. A dilution study using infected lymphocytes from in vitro cultures indicated that a single round of PCR (35 cycles) was able to detect E. salrnonis DNA from approximately 1000 infected cells. Sensitivity was increased with the full nested PCR (35 additional cycles), which detected parasite DNA from 110 infected lymphocytes. The specificity of the PCR was assessed with a panel of microsporidian and myxosporean DNAs. In an experimental infection study, E. salmonis DNA was detected in blood, feces, and tissues of infected chinook salmon but not in uninfected control fish.

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