Mladen Šolić

By Slaven Jozić and Mladen Šolić

We investigated separate and simultaneous effect of temperature, salinity and solar radiation, as well as bacterial strain and origin on Escherichia coli (E. coli) survival in seawater in experimental conditions. The experiments were carried out by placing the bottles filled with seawater of different salinity (15.0, 30.0 and 36.5 psu) and contaminated by bacterial cultures in three light‐protected air incubators set to different temperatures (6, 12, 18 and 24°C), or by placing the bottles in plastic containers filled with water of controlled temperature and exposing them to direct solar light. In experiments in the dark, two typed and two wild E. coli strains were tested. The mean T90 values were 33.55 h for E. coli ATCC 8739, 42.50 h for E. coli ATCC 35218, 72.8 h for E. coli originating from seagull feces and 278.6 h for E. coli originating from sewage, indicating differences between survival abilities among strains. The effect of temperature on T90 was significant only in seagull E. coli at 36.5 psu and sewage E. coli at 30.0 psu and was positive. The effect of salinity was significant only in seagull strain and also was positive. No interactive effect of temperature and salinity was recorded. Experiments in the presence of solar radiation, carried out with two ATCC E. coli strains, demonstrated its dominate harmful effect on bacterial cells, reducing T90 of both strains to 0.30–0.82 h for E. coli ATCC 35218 and 0.31–5.93 h for E. coli ATCC 8739. Within the ultraviolet A (UVA) and photosynthetically active radiation (PAR) spectrum of solar radiation, the wavelengths of 320–360 nm were found as most bactericidal. By comparing survival of cultivated E. coli cells to those in natural seawater samples, significantly higher survival E. coli cells in natural seawater samples was found.

Part of the book: Escherichia coli