SUMMARY: Staphylococcal strains which showed a range of reactions with the phages 47C, 52, 52A, 80 and 81 were examined for changes in phage sensitivity following artificial lysogenization. The lysogenic phages used were isolated from strains of three different phage-typing patterns and differed in serology. The changes in phage reactions thus produced included: (1) immunity to the B phages, 52, 52A and 80 produced by a B phage ; (2) immunity to the A phage 81 produced by a serologically unrelated F phage ; (3) immunity to phage 47 C and sensitivity to phages 52 and 52A produced by a number of A phages. The mechanisms whereby a variety of typing patterns may be obtained within a related group of staphylococci are discussed.

SUMMARY: By the use of anti-bacteriophage sera prepared in rabbits, thirty-nine staphylococcal phages were divided into six serological groups. The first group (A) comprised phages lysing coagulase-positive staphylococci of human origin. They were stable at 20" but inactivated a t 49". They multiplied in broth cultures containing sufficient tryptophan but rarely produced clearing of such cultures. The second group (B) lysed both bovine and human coagulase-positive staphylococci. They were markedly sensitive to heat and required growth factors present in the vitamin B complex. Group C comprised phages of ovine origin which were antigenically related to group B phages and also resembled them in their growth requirements. Group D comprised phage I ( , which lysed both coagulase-positive and negative staphylococci and was antigenically related only to phage W. Phage W belonged to group E and lysed only some coagulase-negative staphylococci. Group F was related in its general characters with the phages of group A.A staphylococcus was found carrying two serologically distinct phages, one of which was detected during the process of adaptation of a phage filtrate to a new propagating strain.Since many strains of staphylococci are lysogenic, lytic filtrates may contain contaminating phages which manifest themselves during adaptation. Adequate serological characterization of the phages used for typing and for investigations of phage-bacterium relationships and of apparent mutation is therefore necessary.

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SUMMARY: The staphylococcal typing phages require divalent cations for a stage in phage growth which is probably that of penetration. When phage is adsorbed to the cell surface of sensitive cocci and a chelating agent is added, there is a short period during which the phage particle may be inactivated and its lethal effect on the coccus prevented. Cocci attacked by phages of serological group A show penetration of the phages in distilled water + CaCl,, or + MgCl, , or to a less extent + SrCl,.The phages of group B are unable to penetrate in presence of SrC1, and in some cases MgCl, is only partially active as compared with CaCl,. Ca ions appear to be required specifically a t a late stage in phage synthesis since the average yield of phage/coccus increases with increasing concentration of CaCl, ; the addition of a chelating agent towards the end of the latent period depresses the yield of phage. were a number of stages in the process of phage invasion. He suggested that the first step of adsorption involved electrostatic forces which were supplied by cations of the medium and which permitted reversible attachment of phage to cell surface. The next step was the separation of the protein and deoxyribonucleic acid components of the phage; this is quickly followed by a process leading to cell killing, and the penetration of deoxyribonucleic acid into the cell and the initiation of phage synthesis in lytic systems. The process of penetration is probably enzymic in nature. The staphylococcal typing phages (Rountree, 1951) require divalent cations for adsorption; this process is inhibited by Na citrate. Each phage has characteristic cation requirements which are related to the phage rather than to the host cell surface. The present paper deals with the role of divalent cations in the different stages of multiplication of staphylococcal phage which follow the first step of adsorption.

SUMMARY: The role of electrolytes in the adsorption of the citrate-sensitive staphylococcal typing-phages and the citrate-insensitive phage K on to their propagating strains was studied in broth+ Na citrate and in distilled water+ CaCI,, MgCl,, and NaCl. Some phages when in the free state were partially inactivated by 1 yo (w/v) Na citrate. In all except two phages, K and 51, citrate inhibited adsorption in broth; adsorption occurred in distilled water. Three phages, 7,42B and 42E, had a specific requirement of 50 pg. CaCl,/ml. for adsorption. With the remainder, the requirements of CaCl, varied from 5 to 400 pg./ml.; similar amounts of MgCl, acted equally well.With the citrate-sensitive phages adsorption in NaCl was variable and, where it occurred, recovery of viable phage from cells infected in NaCl was less than from cells infected in CaCl,. These phages appear to have a specific requirement of divalent cations for adsorption, suggesting that adsorption and penetration are enzymic in character.The electrolyte requirements of the citrate-insensitive phage K were related geometrically to the valence of the cations used, 5 pg. CaCI, or MgCl,/ml. or 25 pg. NaCl /ml. giving optimum adsorption.Early in the study of bacteriophage phenomena it was observed that citrate or oxalate in the media prevented multiplication of certain phages. On the basis of such observations Burnet (1933) proposed that bacteriophages should be divided into ' citrate-sensitive ' or ' -insensitive ', and showed that this sub-division was of value in the classification of phages which lysed intestinal bacteria and staphylococci (Burnet & Lush, 1935).The mode of action whereby citrate and oxalate inhibit phage multiplication has been investigated in detail for only a few phages. The action of these substances is assumed to be due to their de-ionizing effect on calcium and/or magnesium ions, but little information is available on the role which these ions play in phage synthesis (Cohen, 1949). Delbriick (1948) described a mutant of coli phage T4 which required Ca++ as well as tryptophan for adsorption. On the other hand, Adams (1949) showed that coli phage T5 required calcium for growth but not for adsorption. The same was apparently true for the citrate-sensitive coli phage of Elford & Andrewes (1932), coli phage T1 (Puck, 1949), and a staphylococcal phage, 51 (Rountree, 1947). At the same time, citrate may inactivate free phage, although Adams (1949) showed that, with the coli phages, inactivation in salt solutions is due to Na ions rather than to citrate.The present work studies the point in the staphylococcal phage cycle a t which citrate acts and was concerned in the first instance with its effect on 674Phyllis M . Rountree free phage and on adsorption. From this point of departure the role of Ca, Mg and Na ions in phage adsorption has been studied. MATERIAL AND METHODSThe typing phages of Wilson & Atkinson (1945) and phage K and their respective propagating strains were used. Certain of their characteristics have been already described (...