DAO 21:137-143 (1995)  -  doi:10.3354/dao021137

ABSTRACT: The survival of 'atypical', cytochrome oxidase-negative Aeromonas salmonicida in microcosms containing sterilized water and sediment was assessed using the plate count method. The effect of salinity, temperature and presence of sediment was investigated on the survival of 2 strains isolated from ulcerated flounder Platichthys flesus from the northern Baltic Sea. The strains survived for only a short period (< 14 d) when inoculated into microcosms containing only sterilized brackish water (S = 6.4 +/- 0.5o/oo). When sterile sediment was added to the microcosms containing brackish water, the inoculated strains survived for up to 63 d. In microcosms with sterile sediment and fresh water or salt water (S = 30o/oo), the strains survived for a considerably shorter period than in microcosms containing sterile brackish water and sediment. In sterilized water, the strains showed a better survival at 4*C than at 15*C. In water and sediment, a slightly increased survival occurred at 15*C. Adding nutrients (peptone) to the microcosms, when bacteria no longer were recovered by culture methods, did not resuscitate possible non-culturable or dormant cells. These results suggest that 'atypical' A. salmonicida, shed from ulcers of diseased flounders, may survive in the bottom sediment of brackish water environments for a long time. The sediment can thus act as a reservoir for this pathogen, facilitating the spread of the disease.

KEY WORDS: 'Atypical' Aeromonas salmonicida . Ulcer disease . Flounder . Platichthys flesus . Survival