Method for flow cytometric monitoring of Renibacterium salmoninarum inactivation.

The slow growth of Renibacterium salmoninarum limits the usefulness of culture as a research tool. Development of a 2-color flow cytometric assay to quantify the proportions of live and dead R. salmoninarum in a test population is described. Bacteria were simultaneously stained with fluorescein isothiocyanate-conjugated immunoglobulin and exposed to the exclusion dye propidium iodide. Propidium iodide red fluorescence profiles of control groups of untreated and killed R. salmoninarum were compared with those for bacteria exposed to chlorine. Bacterial inactivation was based on mean red fluorescence intensity, and analyzed by high-red fluorescence intensity (HRFI) and curve subtraction (CS) analyses. When the concentration of R. salmoninarum was 8.65 x 10 6 bacteria ml -1 and the bacteria exposed to chlorine at 1 mg l -1 for periods from 1 to 20 min (high-Rs assessment), the mean red fluorescence intensity of the profile for each chlorine-exposure group was higher than that for the untreated control (p 0.99). These results suggest that flow cytometry can be used as a supplementary or alternative method to bacteriological culture for monitoring the inactivation of R. salmoninarum.