F Specific RNA Bacteriophages in Sewage: Methodology and Occurrence

F specific RNA (FRNA) bacteriophages are attractive models for the study of the fate of animal viruses in water treatment processes and pure cultures (MS2, f2) have frequently been used in model experiments. The use of indigenous FRNA phages has been hampered by the lack of selective enumeration methods. Usually, bacteriophages in sewage are enumerated by counting the number of plaques produced in a lawn of an Escherichia coli host strain. Both somatic and F specific phages will contribute to the count. We report the development of a simple and highly selective method, based on a specially constructed host strain of Salmonella typhimurium (WG 49, phage type 3 Nal^r (F'42 lac :: Tn5)). Counts on this host strain normally originate exclusively from F specific phages, because there are only few somatic Salmonella phages in most sewage samples. FRNA phage counts from natural sewage samples using this host strain are more reliable and higher than those obtained on E. coli hosts. F specific bacteriophages were detected in all sewage samples investigated in numbers ranging from 10² − 5 × 10⁴ pfu/ml. Data are presented on the number and types of F specific phages in mixed domestic/industrial sewage; in poultry processing wastewater and in hospital wastewater. The potential of F specific phages as water quality indicators is discussed.