Application of an aqueous acid-fast staining technique to detect pathogens of aquatic species.

Many bacterial and protozoan pathogens in fish and shellfish exhibit acid-fast staining characteristics that are important for pathogen identification and disease diagnosis. The classic acid-fast staining techniques for light microscopy use carbol-fuchsin; a major ingredient of this stain is caustic and hazardous phenol. A new technique using heated aqueous basic fuchsin can stain two acid-fast human pathogens, Mycobacterium tuberculosis and M. avium. This method is a potentially valuable and safer diagnostic tool for aquatic pathologists. M. marinum, a finfish pathogen, and various additional acid-fast parasitic pathogens of finfish and marine invertebrates were stained successfully using this heated aqueous basic fuchsin method.