Toxicity of nitric oxide and peroxynitrite to bacterial pathogens of fish

The inhibitory effect of the nitric oxide (NO) donor S-nitroso-acetyl-penic illamine (SNAP) and the NO and O-2(-) donor 3-morpholino-sydnonimine hydroc hloride (SIN-1) was tested in a cell-free assay. Strains of the bacterial f ish pathogens Aeromonas salmonicida, Renibacterium salmoninarum and Yersini a ruckeri were exposed to different concentrations of the NO donors for 24 h. The results showed that NO possesses inhibitory properties, while peroxy nitrite had no effect. However, when SIN-1 was used in combination with sup eroxide dismutase (SOD) alone or with catalase, an inhibitory effect compar able to that caused by SNAP was seen. The implications of these results are discussed.