A Simple Procedure for Identification of<i>Cytophaga columnaris</i>

Abstract

A simple, time-saving procedure for identifying Cytophaga columnaris, the causative agent of columnaris disease of fishes, is described. The procedure takes advantage of five biochemical or cultural characteristics that, in combination, are believed to be unique to C. columnaris. These characteristics are (1) the ability to grow in the presence of neomycin sulfate and polymyxin B; (2) color and colonial morphology consistent with typical C. columnaris; (3) production of a diffusible, gelatin-degrading enzyme; (4) binding of aqueous Congo red dye in the surface secretions of the suspect colony; and (5) production of a diffusible enzyme that degrades chondroitin sulfate A. The first four characteristics can be observed directly on the original isolation plate; the fifth is observed by using a brief test for the presence of chondroitin AC lyase activity in an agar block excised from the isolation plate. Specific identification of C. columnaris can be made in minutes after visible growth appears on primary isolation plates.