A method for the enumeration of male‐specific bacteriophages in sewage

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Abstract
A method was developed for the selective enumeration of male-specific phages, based on the observation that in sewage there are few phages capable of infecting F--salmonellas, usually < 10 pfu[plaque-forming units]/ml. Using a male Salmonella strain, constructed by the introduction of the plasmid F''42 lac::Tn5 into S. typhimurium phage type 3, plaque counts in secondary effluent were found to be in the range of 60-8200 pfu/ml. Practically all the phages detected had a host range restricted to male Salmonella or Escherichia coli strains, were resistant to CHCl3 and their infectivity was inhibited by RNase. EM of lysates revealed phage particles that were morphologically identical to the male-specific single-strand RNA phages. Similar results were obtained with a strain of S. indiana carrying F''42 lac. A derivative of the S. typhimurium LT2 strain carrying an F-plasmid (F''42 lac fin P301) derepressed for fertility inhibition by the resident plasmid pSLT was equally sensitive to male-specific phages, but from sewage samples many other phages infecting F- E. coli but not F- Salmonella were isolated using this host strain.