The survival capacity of an Aeromonas hydrophila strain (named SB14) isolated from mineral water was investigated in an artificial mineral water microcosm. The bacterial count of this microorganism was compared with two strains of other species from aquatic environments (Pseudomonas fluorescens SSD and Pseudomonas putida SSC) and a bacterium indicative of faecal pollution (Escherichia coli ATCC 25922). Among the strains, all added to sterile Pyrex glass flasks (1 l) to yield a final bacterial count of about 5 x 10(6) CFU/ml, A. hydrophila SB14 showed a quite strong survival capacity (150 days), even though the Pseudomonas strains were better adapted to this habitat (more than 240 days). E. coli ATCC 25922 was the least well fitted to survive and was no longer detected after 70 days. When A. hydrophila SB14 was inoculated together with one or two of the above strains, its survival appeared to be dependent on interaction with other organisms. A marked decrease in survival by 30 days, possibly due to antagonistic interaction, was observed when this microorganism was associated with E. coli ATCC 25922, and an increase by 30 and 60 days, possibly due to commensalic interaction, was obtained when A. hydrophila SB14 was inoculated with P. fluorescens SSD or P. putida SSC, respectively.