Effect of Penicillin on the Reaction Between Phage and Staphylococci

Abstract

In Fleming's original paper on penicillin, 1 he described the lysis of staphylococci by this agent. Since then the lytic process and ancillary morphologic changes in the bacteria concerned have been studied by several investigators. 2 3 4 5 6 7 8 We wish to report here the effect of penicillin on the lytic action of bacteriophage.∗

The phage employed in our experiments is the “K” race; it and the homologous strain of Staphylococcus aureus have been used in studies described in a series of papers appearing since 1929. Stock cultures were grown in Roux flasks for 18 hours at 36°C. In order to have a substrate of actively growing cells, 1 × 10⁸ staphylococci/ml were suspended in 100 ml of broth contained in a 500 ml flask; aeration was provided by placing the flask in a shaker operating in a water bath set at 36°C. When growth had progressed to a level of 1 × 10⁹ bacteria/ml, the cell suspension was removed from the shaker and used for the experiments described below. To determine [bacteria] when values were >5 × 10⁸ staphylococci/ml, the direct microscopic count method was employed. For lytic curves, visual comparison was made with standards covering a range from 2 × 10⁷ to 5 × 10⁸ staphylococci/ml in formalinized broth. The fluid medium throughout was tryptose phosphate broth. Phage determinations were carried out by Gratia's method 9 of counting plaques and the values noted below are in plaques/ml.

A 10 ml mixture containing 5 × 10⁸ staphylococci/ml, 5 × 10⁸ phage units/ml and 10 units of sodium penicillin/ml was placed in a test tube and shaken at 36°C. Turbidity readings were made every 0.2 hour. This was also done with a suspension from which the phage was omitted and with one containing no penicillin.