Photoreactivation of total heterotrophic bacteria in bottled drinking water after inactivation with pulsed ultra-violet light

Abstract

Bacteria which cause opportunistic infections such as Pseudomonas can self resuscitate in
circumstances where effective UV disinfection is compromised and is exposed to sunlight. The study investigated the effect of sub-lethal doses of pulsed ultra-violet (PUV) light on total heterotrophic bacteria (THB) in three brands of bottled water packed in glass and plastic bottles and how photoreactivation and dark repair occurred. The effect of exposure time on photoreactivation of Escherichia coli and Pseudomonas aeruginosa after inactivation with PUV was also investigated. THB in brands 1, 2 and 3 were completely inactivated by 7, 3 and 5 pulses of UV light respectively. Light repair of THB varied in the three brands of bottled water due perhaps to differences in the ionic composition of the three brands. Brands 1, 2 and 3 having 0.4, 0.7 and 1.7 log units of repair. respectively. Evidence of dark repair was not significant. Photo-repair in E. coli and Pseudomonas aeruginosa increased gradually with continual exposure to irradiating light for a period after which there was a decrease, suggesting that for a particular bacterium and illuminating source, an optimum time of exposure exist during which maximum photo-repair occur.