The simultaneous effect of temperature, salinity and solar radiation, as well as the history and strain of bacterial cells on Escherichia coli (E. coli) survival in seawater under experimental and natural conditions were studied. The experiments were carried out within the natural range of temperature (12 degree C, 18 degree C and 24 degree C) and salinity (30.0 psu and 36.5 psu). Natural samples of microbiologically contaminated sea water were taken during September 2011, when the temperature and salinity of sea water were stable (23-24 degree C, 36-37 psu). In the absence of solar radiation, the mean T sub(90) values differed, depending on the bacterial strain and were 42.50 h for E. coli ATCC 35218 and 33.55 h for E. coli ATCC 8739. No significant effect of temperature or salinity on T sub(90) was found, but a strong and significant negative effect of solar radiation on T sub(90) of both E. coli strains was recorded. Depending on the bacterial strain, the dominant effect of solar radiation reduced the T sub(90) of E. coli by 15- to 70-fold. Within the ultraviolet A (UVA) and photosynthetically active radiation (PAR) spectrum of solar radiation, the wavelengths of 320-360 were found to be most bactericidal. If exposed to solar radiation, sea water samples were found to be depleted of culturable E. coli cells even during 24 h storage under appropriate conditions. A higher resistance of wild E. coli cells to the negative effects of environmental conditions than cultivated cells was also found.