In a series of papers beginning in 1933 Levine and Frisch have affirmed that extracts derived from susceptible cultures of Salmonella block the lytic activity of bacteriophages active against that group of bacteria. These investigations have been confirmed by Burnet (1934), utilizing organisms and phages belonging to the same group as well as several strains of Shigella. These extracts apparently reflect quite accurately those surface antigenic components responsible for bacteriophage absorption on living and heat-killed susceptible cultures.In the course of our studies with staphylococcus bacteriophages we have been struck by the fact that these phages are exceedingly difficult to isolate from sources rich in phages for members of the enteric group. It may very well be that one of the factors con-

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The London Food Centre was launched in February 1999 by the Ministry of Agriculture Fisheries and Food to help small and medium‐sized food businesses expand and improve their profitability. The London Food Centre gives food businesses an enhanced knowledge of the technology and science that lies behind their products and processes. This knowledge enables them to raise the efficiency, reliability and safety of their operations as well as increasing the quality and diversity of their product range.

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