Effects of sub-lethal gamma irradiation on antibiotic susceptibility profile and population dynamics of Enterococcus faecalis and Escherichia coli in water

Disinfection of water is important in the control of waterborne diseases. It is used to kill or inactivate microorganisms in a gradual process that involves a number of physical–chemical and biochemical processes. The effects of sub-lethal gamma irradiation on survival and resistant pattern of two indicator organisms used in assessing water quality: Enterococcus faecalis and Escherichia coli were investigated in this study. Plate count agar and disc diffusion methods were used to determine the load and antibiotics susceptibility pattern of the test organisms respectively before and after exposure to different doses of gamma irradiation in sachet water samples. Survival pattern of the two indicator organisms to gamma- ray showed a decline in the populations of the organisms with time compared to the controls (non-radiated). The effect of the irradiation on the E. coli was dose dependent, it initially responded to the effects of the irradiation in the first 4 days of exposure compared to the control. On exposure to 4 and 5 gy gamma rays a minimum population was reached on the 7^th day. At p<0.05 the population of E. coli was significantly different from the control. The survival pattern of Ent. faecalis also followed a similar growth pattern. The application sub-lethal gamma irradiation did reduce the population of the isolates and also affect the antibiotic susceptibility of the isolates.