Pretreatment to reduce somatic salmonella phage interference with FRNA coliphage assays: successful use in a one-year survey of vulnerable groundwaters

Abstract

Somatic salmonella (SS) phages were commonly found in higher numbers than F-specific RNA (FRNA) coliphages in a multi-site survey of contamination-vulnerable groundwaters. The relative abundance of SS phages required that a pretreatment procedure be implemented to reduce the SS phage content of samples before FRNA coliphage assay with Salmonella typhimurium WG49. Pretreatment involved selective SS phage removal by Salm. typhimurium WG45 cells. This pretreatment proved effective in producing interference-free samples throughout the one-year survey period and in seeded evaluation, was shown not to affect the detection of representative FRNA coliphage MS2. During the survey, 30 groundwater sites located in the continental United States, Puerto Rico and the Virgin Islands were examined for FRNA coliphages and SS phages at monthly intervals. FRNA coliphages were detected at six of the 30 sites and in 33 of 329 monthly samples. SS phages were also detected at six sites and in 28 of 329 monthly samples. Five of the phage-positive sites were positive for both phage groups. At those five sites, 58 monthly samples were collected during the survey period. Those 58 samples yielded an average FRNA coliphage concentration of 140 pfu per 100 l of groundwater as compared to an average SS phage concentration of 565 pfu per 100 l of groundwater. Twenty of the 58 samples were positive for both the FRNA coliphages and SS phages. In those samples, FRNA coliphages were more abundant in five samples; SS phages were more abundant in 15 samples. Because these results demonstrate that SS phage levels may often exceed FRNA coliphage levels in environmental waters, it is clear that SS phage removal procedures will greatly enhance the effectiveness of the WG49-based FRNA coliphage assay.

Bacteriophages as indicators of enteric viruses and public health risk in groundwaters

“…For example, while F ¦ coliphages are generally specific for Escherichia coli, they may also attack and multiply in other coliforms and Enterobacteriaceae (Bradley 1967;Dhillon et al 1970;Dhillon and Dhillon 1974;Rhodes and Kator 1991;Ackerman, et al 1992). Also, the male host cell can undergo FDNA coliphage attack, as well as somatic coliphage attack (Qureshi and Qureshi 1991;Qureshi et al 1988;Debartolomeis and Cabelli 1991;Rhodes and Kator 1991;Williams and Stetler 1994;Hsu et al 1996;Sinton et al 1996;Stetler and Williams 1996). Accordingly, because they are not specific to the E. coli host and are not normally found in the faeces of humans, they cannot be good indicators of the presence of faecal contamination and enteric viruses (Furuse et al 1983;Havelaar et al , 1986Havelaar et al , 1990Furuse 1987).…”

Male-specific RNA coliphages detected by plaque assay and RT-PCR in tropical river waters and animal fecal matter

“…However, the sensitivity of plaque assays for the detection and enumeration of FRNA coliphages is affected by factors such as the growth condition of the host affecting the formation of pili for coliphages to attach and infect host cells, low numbers of FRNA coliphages in the sample tested and interference from somatic phages present in the same sample (Havelaar et al 1990;Stetler & Williams 1996;Woody & Cliver 1995). As an alternative, highly sensitive and specific PCR assays have been designed for the detection of FRNA coliphages (Rose et al 1997), but cost and technical complexities have prevented their wide-spread use in environmental monitoring programs.…”

An Analytical Method for Trifluoroacetic Acid in Water and Air Samples Using Headspace Gas Chromatographic Determination of the Methyl Ester

“…Average exposures for U.S. residents were estimated at 0.01 to 0.014 organisms for a 7-day per annum period of exposure. Stetler and Williams (1996) found that the effectiveness of the WG49 FRNA coliphage assay for the detection of fecal contamination was improved significantly by the pretreatment of samples for the removal of somatic Salmonella (SS) phages. SS reduction in groundwater samples could be accomplished by the addition of Salmonella typhimurium WG45 cells to the samples to adsorb the SS phages.…”