© by PSP Volume 23 – No 8. 2014 Fresenius Environmental Bulletin 1852 EFFECT OF SOLAR RADIATION, TEMPERATURE AND SALINITY ON THE SURVIVAL OF TWO DIFFERENT STRAINS OF ESCHERICHIA COLI Slaven Jozić 1, *, Mira Morović 1 , Mladen Šolić 1 , Nada Krstulović 1 and Marin Ordulj 2 1 Institute of Oceanography and Fisheries, Split, Croatia 2 Univesity of Split, University Department of Marine Studies, Split, Croatia ABSTRACT The simultaneous effect of temperature, salinity and solar radiation, as well as the history and strain of bacte- rial 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 o C, 18 o C and 24 o C) and salinity (30.0 psu and 36.5 psu). Natural samples of microbiologically con- taminated sea water were taken during September 2011, when the temperature and salinity of sea water were sta- ble (23–24 o C, 36–37 psu). In the absence of solar radia- tion, the mean T 90 values differed, depending on the bac- terial 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 90 was found, but a strong and significant negative effect of solar radiation on T 90 of both E. coli strains was recorded. Depending on the bacterial strain, the dominant effect of solar radiation reduced the T 90 of E. coli by 15- to 70-fold. Within the ultraviolet A (UVA) and photosynthetically active radiation (PAR) spec- trum of solar radiation, the wavelengths of 320–360 were found to be most bactericidal. If exposed to solar radia- tion, sea water samples were found to be depleted of cul- turable E. coli cells even during 24 h storage under ap- propriate conditions. A higher resistance of wild E. coli cells to the negative effects of environmental conditions than cultivated cells was also found. KEYWORDS: Escherichia coli, bacterial strain, survival, tempera- ture, salinity, solar radiation 1. INTRODUCTION When indicator organisms enter the marine environ- ment, they experience a very hostile environment. The hostile impact of the marine environment to these organ- isms is reflected in the negative effects of the complex * Corresponding author array of physical, chemical and biological factors of the marine environment, with a dominant effect of tempera- ture, salinity and solar radiation [1-4]. The distribution and number of indicator bacteria de- pends mostly on their input, but also on environmental factors [5] and adaptation capacity. The adaptation capac- ity of microbial cells to marine conditions is very minor, which leads to physiological injury that might be sub- lethal [6, 7] or lethal [8, 9]. If exposed to the negative effect of some abiotic factors, particularly to solar radia- tion, indicator bacteria rapidly enter into a temporary state in which they lose culturability on standard bacteriologi- cal media, but can still maintain some metabolic activity [10, 11], infective capacity and potential for pathogenicity [12, 13]. If further exposed to an unfavourable marine environment, bacterial cells are irreversibly damaged and die. For how long they will maintain culturability and sur- vive in sea water, depends on many factors, such as the intensity of environmental factors and the characteristics of the bacterial cell, where besides the origin and pre- exposure history, the bacterial strain plays an important role [4, 14, 15]. Although there are many studies in which the effects of the aforementioned parameters have been addressed, their simultaneous effects have been poorly investigated. This study is the first report of the separate and simultaneous effect of temperature, salinity and solar radiation, as well as the history and strain of E. coli cells on their survival in sea water. 2. MATERIALS AND METHODS 2.1 Experiments with pure bacterial cultures Experiments were performed with two different E. coli strains that showed completely different morphological characteristics on standard Tryptone bile X-glucuronide (TBX) plates: E. coli ATCC 35218 originating from canine faeces and E. coli ATCC 8739 originating from human faeces. Bacterial suspensions for experiments were ob- tained from pure cultures of test microorganisms incu- bated on mineral-modified glutamate broth (MMGB). Bac-