Bacteriophages: update on application as models for viruses in water

Abstract

Phages are valuable models or surrogates for enteric viruses because they share many fundamental properties and features. Among these are structure, composition, morphology, size and site of replication. Even though they use different host cells, coliphages and Bacteroides fragilis phages predominantly replicate in the gastro-intestinal tract of humans and warm-blooded animals where enteric viruses also replicate. A major advantage of phages is that, compared to viruses, they are detectable by simple, inexpensive and rapid techniques. In view of these features, phages are particularly useful as models to assess the behaviour and survival of enteric viruses in the environment, and as surrogates to assess the resistance of human viruses to water treatment and disinfection processes. Since there is no direct correlation between numbers of phages and viruses, phages cannot to a meaningful extent be used to indicate numbers of viruses in polluted water. The presence of phages typically associated with human and animal excreta indicates the potential presence of enteric viruses. However, the absence of these phages from water environments is generally a meaningful indication of the absence of enteric viruses. This is because phages such as somatic coliphages, F-RNA coliphages and B. fragilis phages generally outnumber enteric viruses in water environments, and they are at least as resistant to unfavourable conditions including those in water treatment and disinfection processes. However, using highly sensitive molecular techniques viruses have been detected in drinking water supplies which yielded negative results in conventional tests for phages. Initially, data on phages were rather confusing because a wide variety of techniques was used. However, techniques for the detection of phages are being standardised internationally. This applies in particular to somatic and F-RNA coliphages, and B. fragilis phages, which are most commonly used in water quality assessment. Reliable and practical techniques now available include direct quantitative plaque assays on samples of water up to 100 ml, and qualitative tests on 500 ml or more using highly sensitive enrichment procedures.

Use of coliphages to evaluate water treatment processes and determine faecal contamination origin of source waters

“…Somatic and FRNA coliphages can be relied on because they are relatively simple and can be detected rapidly. Moreover, they are always present in the faeces of many warm-blooded animals as indicators of faecal pollution, when compared to bacteria (Grabow 2001). This study was designed to evaluate the general efficiency of sedimentation (after coagulation/flocculation) and filtration processes used prior to the chlorination of the final water in the Temba, Klipdrift and Wallmannsthal WTPs in the removal of viral indicators (somatic and FRNA coliphages) and to determine the source of faecal pollution with a view to water source management.…”

“…This would result in a substantial reduction in turbidity at each stage. The effectiveness of virus removal during water treatment may also be affected by factors that act against particle association (floc formation), such as pH and temperature conditions (Grabow 2001;LeChevelier and Au 2004). Although, on average, the pH values recorded were within the recommended limits (pH 6-9), there were maximum values of 9.50 and 9.78 in settled water and of 9.41 and 9.62 in water samples collected after filtration from Temba and Klipdrift, respectively.…”

“…After filtration, almost similar maximum temperatures were found in both the Temba (26.4°C) and Klipdrift (26°C) samples, with the maximum temperature values above the limit (Table 2). Maintaining a temperature of B25 o C in accordance with the recommended standards (SANS: 241, 2006) is essential not only for the efficacy of the physicochemical reactions and preventing the toxicity of metals that most could possibly be found in the water (USEPA 1999(USEPA , 2001Momba et al 2006a), but also for promoting the inactivation of viruses in water (Grabow 2001;Cole et al 2003;Duran et al 2002). Collectively, virus removal and inactivation may be effectively achieved by increased temperatures and extremes of pH (Sinton et al 1999;Feng et al 2003).…”

Field-based evaluation of a male-specific (F+) RNA coliphage concentration method

“…FRNA coliphages proliferate in the gastrointestinal tract of warmblooded animals, are shed exclusively in feces and loosely display similar sensitivities to several chemical and environmental stresses in comparison to enteric viruses (Grabow, 2001;Havelaar et al, 1993). It has also been demonstrated that FRNA coliphages are indicative of the presence and persistence of human enteric viruses in various water types and shellfish (Bae and Schwab, 2008;Doré et al, 2000;Havelaar et al, 1993).…”

“…Multiple strategies have been developed to concentrate viruses from water, including electronegative and electropositive filters (Ikner et al, 2012). However, these filters are prone to clogging, viral elution is achieved in relatively large volumes (10 ml to 300 ml) adding undesirable dilution effects and elution buffers are often of extreme pH or protein content which may limit downstream detection (Grabow, 2001;Ikner et al, 2012;Paar et al, 2015).…”