A correlation between serology, buoyant density, and morphology has been demonstrated for six serological groups of staphylococcal phages. Four morphological types have been observed and represent the following serological groups: (i) group A, (ii) groups B, F, and L, (iii) group D, and (iv) group G. The correlations were useful in the detection of serological variation among several staphylococcal typing phages. Staphylococcal phages have been grouped by Rountree (1949) and Rippon (1956) by serology and other properties. Seto, Kaesberg, and Wil

Ethidium bromide (EB) was more efficient than ethyl violet or rifampin as a curing agent for the penicillinase plasmids of Staphylococcus aureus strains. The effects of EB on growth and on the loss of the penicillinase plasmid of PS 81 were studied in detail. The growth rates of PS 81 and an EB-cured derivative were identical in broth, but the cured derivative had a shorter lag in the presence of added 6 x 10-6 M EB. The shortened lag was due to prior exposure to EB as the cured derivative and an EB-treated but uncured strain of PS 81 gave identical growth lag and growth rates in the presence of EB. The curing of PS 81 by EB occurs in three phases. After a 4 to 5 hr lag, there is a 100-fold increase in the number of penicillinase-negative cells, and the proportion of cured cells continues to rise until 10 to 12 hr. Thereafter, the population becomes refractory to further curing, and the proportion of penicillinase-negative cells remains constant at about 20% of the total. Penicillinase-positive survivors of EB treatment showed increased EB resistance and were cured at lower rates upon subsequent EB treatment. Isolated colonies of the parental strain PS 81 were heterogeneous in their EB sensitivity. Thus, EB does not competitively favor spontaneously cured penicillinase-negative cells but appears to act in a manner analogous to acridine orange on the plasmids of enteric bacteria.Plasmid elimination. The method of Bouanchaud, Scavizzi, and Chabbert (4) was used for plasmid elimi-1200 on August 1, 2020 by guest

The effectiveness of Staphylococcus aureus strain 8325-4 as a recipient for the transduction of methicillin resistance requires the presence of a penicillinase plasmid but was found to be independent of the lysogenic state of the recipient. Effectiveness is conferred by the plasmid in either the autonomous or integrated states, although the transduction rate is higher in the former. Once established, the maintenance and expression of methicillin resistance were independent of continued carriage of the plasmid deoxyribonucleic acid. Analysis of penicillinase plasmid mutants indicated that beta-lactamase production was the plasmid function responsible for recipient effectiveness. Supportive evidence included the abrogation of recipient effectiveness by the beta-lactamase inhibitor clavulanic acid and the elimination of a plasmid requirement with recipient strains carrying a chromosomal beta-lactamase determinant. A possible role for beta-lactamase production in the transduction of methicillin resistance is discussed.Methicillin resistance to Staphylococcus aureus is an intrinsic form of resistance of the bacteria to certain semisynthetic penicillins and cephalosporins (37). Although the exact mechanism of the resistance is unknown, it is not mediated by inactivation of the drug (15, 36). Early reports suggested that the determinant for methicillin resistance (mec) was plasmid-borne (10,17), but genetic studies now strongly support a chromosomal location for the mec determinant (6,16,39).Genetic analyses of mec were initially difficult due to the low-frequency transfer of the resistance seen in vitro. However, procedures for the transduction of methicillin resistance were developed by Dornbush et al. (10) and by Cohen and Sweeney (6). The latter investigators reported that for S. aureus strain to be an effective recipient in a methicillin resistance transduction (hereafter referred to as recipient effectiveness), it must be lysogenic for 411 or a related prophage and, with few exceptions, must carry a penicillinase plasmid (6-8). The genetic contributions of the plasmid and prophage in conferring recipient effectiveness upon their 8325-4 host remained obscure.In this study, we examined the roles of the prophage and plasmid in conferring recipient effectiveness. We were unable to demonstrate a requirement for a resident prophage, but a requirement for a penicillinase plasmid was confirmed. Evidence is presented supporting the conclusion that the plasmid function which promotes recipient effectiveness is beta-lactamase production. MATERIALS AND METHODSBacteria and bacteriophage. The staphylococcal strains used in this study and their relevant characteristics are given in Table 1. Strains bearing the pI9789 and p181 plasmids were obtained from our laboratory stock collection. The remaining plasmid species originated from strains obtained from R. Novick. All plasmids were transduced into strains GS450 or GS451 unless otherwise noted. Phages 53 and 80 are staphylococcal typing phages, phage 80a is a host range variant ...

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Dowell , C. E. (The University of Texas, Dallas) and E. D. Rosenblum . Serology and transduction in staphylococcal phage. J. Bacteriol. 84: 1071–1075. 1962.—A triply lysogenic strain of Staphylococcus aureus was shown to carry a serological group B phage capable of transduction. Three typing phages (53, 80, 42D), either belonging to serological group B or having a close association with it, were also shown to have transducing ability. A rapid screening method was used to isolate two new transducing phages, both of which belonged to serological group B. Propagating strain 42B/47C was found to carry a transducing phage that was neutralized by both group B and group F antisera. Nine other phages belonging to serological groups other than group B did not have generalized transducing ability, nor did three group B typing phages that were atypical in their calcium requirement. It was postulated that transducing ability is associated with staphylococcal phages of serological group B and with related phages of group F.