Effect of sunlight on the survival of Escherichia coli

Abstract

An experimental micro environment containing seawater with 33 to 35 salinity and 7.23 – 7.56 pH values was analyzed, where the temperature-related solar radiation was tested for its effect on a sample of Escherichia coli isolated from the water of a stormwater pipeline draining at Mucuripe beach, Fortaleza, Brazil. The systems contained in amber-color, transparent flasks were exposed to sunlight over a 10-day period, while an incubated system under absence of sunlight (laboratory medium) was held as control. E. coli was found to show viability up to 216 hours even under exposition to sunlight, although a sharp decrease was observed in the microbrial population as from 96 hours, mainly when the data for sunny days where compared to those of cloudy days and to the control system. Temperature was always high in sunny days, so that survival of E. coli was shown to increase in cloudy days and to decrease as a function of exposition time, but without statistical interaction between those two factors. An inverse correlation was found to occur between number of viable cells of E. coli. and time of exposition of the strain to solar radiation.