SURVIVAL OF ATYPICAL AEROMONAS-SALMONICIDA IN WATER AND SEDIMENT MICROCOSMS OF DIFFERENT SALINITIES AND TEMPERATURES

The survival of 'atypical', cytochrome oxidase-negative Aeromonas salm onicida in microcosms containing sterilized water and sediment was ass essed using the plate count method. The effect of salinity, temperatur e and presence of sediment was investigated on the survival of 2 strai ns isolated from ulcerated flounder Platichthys flesus from the northe rn Baltic Sea. The strains survived for only a short period (< 14 d) w hen inoculated into microcosms containing only sterilized brackish wat er (S = 6.4 +/- 0.5 parts per thousand). When sterile sediment was add ed to the microcosms containing brackish water, the inoculated strains survived for up to 63 d. In microcosms with sterile sediment and fres h water or salt water (S = 30 parts per thousand), the strains survive d for a considerably shorter period than in microcosms containing ster ile brackish water and sediment. In sterilized water, the strains show ed a better survival at 4 degrees C than at 15 degrees C. In water and sediment, a slightly increased survival occurred at 15 degrees C. Add ing nutrients (peptone) to the microcosms, when bacteria no longer wer e recovered by culture methods, did not resuscitate possible non-cultu rable or dormant cells. These results suggest that 'atypical' A. salmo nicida, shed from ulcers of diseased flounders, may survive in the bot tom sediment of brackish water environments for a long time. The sedim ent can thus act as a reservoir for this pathogen, facilitating the sp read of the disease.