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Water Research 38 (2004) 2614–2618

Rapid enumeration of virus-like particles in drinking water samples using SYBR green I-staining
Johanna M. Rinta-Kantoa,1, Markku J. Lehtolaa,*, Terttu Vartiainena,b, Pertti J. Martikainenb
b

Department of Environmental Health, National Public Health Institute, P.O. Box 95, FIN-70701 Kuopio, Finland Department of EnvironmentalSciences, University of Kuopio, Bioteknia 2, P.O. Box 1627, FIN-70211 Kuopio, Finland Received 22 May 2003; received in revised form 23 February 2004; accepted 5 March 2004

a

Abstract We studied the suitability of SYBR green I-staining for determining total counts of virus-like particles and bacteria in drinking water. Low background fluorescence and lack of unspecific staining made drinking watersamples an excellent matrix for SYBR green I-staining. Direct microscopic count method is a rapid and economical tool for assessing the total number of virus-like particles in aquatic samples, compared to culture-dependent or molecular biology methods. We applied this method to show the efficiency of a large-scale drinking water purification process in the removal of virus-like particles and bacteriafrom lake water. r 2004 Elsevier Ltd. All rights reserved.
Keywords: Drinking water; Viruses; Bacteriophage; SYBR green I; Bacteria

1. Introduction Despite the extremely oligotrophic character of the habitat, drinking waters harbour a diverse and active microbial community, consisting of bacteria, fungi, yeasts and protozoa [1]. Natural waters and drinking water distribution systems arephysically linked to each other when surface water from lakes or rivers is used as the raw water for drinking water purification. Despite the multi-step process, a small fraction of microbes pass through the drinking water purification and become established in the microbial community of a distribution network causing hygienic, aesthetic and technical problems. To solve and understand these problems,drinking water purification processes, drinking water

*Corresponding author. Tel.: +358-17-201371; fax: +35817-201155. E-mail address: markku.lehtola@ktl.fi (M.J. Lehtola). 1 Present address: Department of Microbiology, University of Tennessee, Knoxville, TN 37996, USA.

chemistry and microbiology and their effects on microbial growth have been intensively studied. The occurrence of viruses indrinking water is commonly considered to be a result of a failure in the water treatment process or in the distribution network, causing a potential risk to public health. The use of culture-based detection methods, and a focus only on viruses pathogenic to higher forms of life, have led to the presumption that viruses are rarely present in drinking water. Studies of viruses in drinking waters havemainly concentrated on screening the water for potential pathogens and studying the survival potential of pathogenic viruses in the drinking water distribution system. In several studies, selected bacteriophages have been used as indicators of fecal contamination of drinking water, or as model viruses for enteric viruses because of their similar properties in transport and survival [2,3]. In lakeand sea water environments, bacteriophages are estimated to be the most numerous component of plankton, with abundance ranging from 104 to 108 viruses mlÀ1 [4]. Enumeration of virus particles has

0043-1354/$ - see front matter r 2004 Elsevier Ltd. All rights reserved. doi:10.1016/j.watres.2004.03.008

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J.M. Rinta-Kanto et al. / Water Research 38 (2004) 2614–2618 2615

becomean essential part of studies in the field of aquatic microbial ecology during the 1990s. The abundance of viruses in natural water samples was first assessed solely with transmission electron microscopy (TEM) [5,6]. Soon it was realized that it was possible to visualize virus particles with techniques combining bright nucleic acid stains and epifluorescence microscopy [7–10]. Enumeration of...