Improved Specificity in Detecting F-Specific Coliphages in Environmental Samples by Suppression of Somatic Phages

Analysis of environmental waters for F-specific coliphages on the genetically constructed host Salmonella tvphimurium strain WG49 is hampered by the detection of Bomatic Salmonella phages. To improve the specificity of F-specific coliphage detection, two agents were tested for selective inhibition of Salmonella phage infectivity: heat-killed cells of female (F) S. tvphimurium WG45 and chemically extracted S. tvphimurium lipopolysaccharide (LPS). When both treatments were tested on pools of environmental isolates of Salmonella phages and the FRNA coliphage MS2, Salmonella phage infectivity was reduced by >90% with no change in MS2 detection. When environmental waters were tested by single agar layer or membrane filter methods, LPS increased the selectivity of F-specific coliphage detection from 28% to >90%, with no loss of sensitivity. The results of this study indicate that LPS effectively inhibits Bomatic Salmonella phage infectivity when added directly to a water sample or to molten agar medium or when used to treat filters on which phages have been concentrated.