Response of Different Strains of Enterococcus faecalis to UV Inactivation after Freezing

Abstract

Abstract-Response of two strains of Enterococcus faecalis bacteria, ATCC strain 29212 and ATCC strain 51299 (vancomycin resistant) to UV inactivation after survived freezing treatment was examined. The test microorganisms were frozen at -7 °C, -15 °C or -30 °C with one, three or five freeze and thaw cycles prior to UV irradiation to investigate the effect of freezing temperature and freeze thaw cycles on the efficacy of UV inactivation. Experimental results suggest that freezing influenced the response of Enterococcus faecalis cells to UV irradiation. Freezing treated cells behaved differently compared to those had not frozen.Index Terms-Enterococcus faecalis, freezing treatment, UV disinfection, waterborne pathogens, water and wastewater treatment. I. INTRODUCTIONConventional municipal wastewater treatment systems can significantly reduce the population of microorganisms; however, after treatment wastewater treatment plant (WWTP) effluents may still contain high numbers of fecal bacteria. Published research data indicated that the portion of pathogenic and antibiotic resistant bacteria in WWTP effluent remained at significant concentrations or even increase [1]- [5]. Release of pathogenic and antibiotic resistant microorganisms with WWTP effluents is a growing public health concern [6], [7]. Multiple antibiotic resistant fecal coliforms and enterococci including vancomycin resistant Enterococcus (VRE) have been detected in influent, effluent, and sludge from municipal wastewater treatment plants [8][9]. WWTPs provide a favorable environment for gene transfer due to high bacterial densities and nutritional richness of the influents [4], [8], [9]. Applications of UV disinfection in water and wastewater treatment systems have increased in recent years in Canada. Numerous research has been carried out to find the correlations between water quality, bacterial sensitivity and UV disinfection efficiency [10]-[12], the impact of cold temperatures on UV disinfection processes, especially, the responses of the pathogenic microorganisms after experiencing freezing to UV is however seldom examined [13], [14]. As a treatment alternative, natural or mechanical freezing has been used for various water or wastewater treatment, sludge pre-treatment or conditioning, and desalination [15]-[19]. Depending on the requirements of the finished water quality, UV disinfection may be needed after freezing treatment. Waterborne microorganisms might behave differently to UV Manuscript received December 5, 2012; revised February 27, 2013. W. Gao is with Department of Civil Engineering, Lakehead University, Thunder Bay, ON, Canada (e-mail: wagao@lakeheadu.ca).irradiation after survived freezing compared to those without experience freezing [13], [14], [20]. A recent study by Williams at al. [14] revealed that after freezing waterborne microorganisms such as Escherichia coli, Enterococcus and Bacillus behaved differently to UV irradiation compared to those had not frozen. Freezing affected the response of these microbes, a lower UV inactivat...

Effects of salinity and temperature on inactivation and repair potential of Enterococcus faecalis following medium- and low-pressure ultraviolet irradiation

“…). Such inactivation behaviour had previously been reported by Gao and Williams () when they studied the behaviour of various Ent. faecalis strains (ATCC strain 29212 and ATCC strain 51299) to UV inactivation.…”

“…The presence of the tailing was observed in the MP and LP disinfection curves, possibly due to shielding or clumping of the bacteria and phenotypic persistence (Pennell et al 2008). Such inactivation behaviour had previously been reported by Gao and Williams (2013) when they studied the behaviour of various Ent. faecalis strains (ATCC strain 29212 and ATCC strain 51299) to UV inactivation.…”

“…High temperature (25°C) favoured MP and LP UV disinfection with high inactivation rates and levels. Likewise, a lower LP UV inactivation level was observed in the freezing treated waterborne micro-organisms compared to those had not frozen in general (Williams et al 2011;Gao and Williams 2013). Higher inactivation rates and levels were observed at very high temperature (45 or 50°C), and lower inactivation rates and levels at very low temperature in wastewater (5 or 10°C) (Abu-ghararah 1994; Mounaouer 2012).…”

“…; Venieri et al . ; Gao and Williams ), while information on the comparison of the response of Ent. faecalis to LP and MP UV inactivation is quite scarce.…”

“…For Ent. faecalis, one of the most common species of enterococci (Stevenson et al 1994), which was selected as an indicator micro-organism in this study, many studies have been conducted on water disinfection by LP UV technology (Hassen et al 2000;Koivunen and Heinonen-Tanski 2005;Ananou et al 2010;Venieri et al 2011;Gao and Williams 2013), while information on the comparison of the response of Ent. faecalis to LP and MP UV inactivation is quite scarce.…”