Isolation of a Rickettsiales-Like Organism from Diseased Coho Salmon (Oncorhynchus kisutch) in Chile

Abstract

A rickettsiales-like organism was isolated in cell culture from coho salmon (Oncorhynchus kisutch) reared in seawater net pens in the vicinity of Puerto Montt, Chile S. A. and experiencing an epizootic with accompanying mortality. The organism, observed in fish and isolated in cell culture, was GRAM-negative, pleomorphic, predominantly coccoid in shape, and approximately 1μm in diameter. It replicated, producing cytopathic effect (CPE) in cell lines from four species of salmonids, but failed to grow in any of eleven standard bacteriological media. The optimal temperature for replication was 15-18°C based on the production of CPE. Streptomycin, gentamicin, and tetracycline were inhibitory for the organism, but it was not sensitive to penicillin.
The isolated organism stained with GIEMSA and PINKERTON'S stains and with a modified GIMENEZ stain. It did not react with a monoclonal antibody against the group-specific LPS chlamydial antigen. On the basis of available information, we suggest this organism is a member of the order Rickettsiales and represents the first isolation of a member of this group from an aquatic poikilotherm.