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The Shigella flexneri phage Sf6 has an isometric head with hexagonal symmetry 53nm in diameter. The noncontractile tails in 16 nm long and terminates with a base plate containing six spikes. Sf6 is typical of the C phages in the morphological classification of Bradley. Phage Sf6 processes alpha-1,3-endorhamnosidase activity as demonstrated by methylation and reducing end group sugar analyses of the products obtained on interaction with the O-polysaccharide chain of S.flexneri strains which have the O-group 3,4 antigen. The major end product was an octasaccharide with the following structure: Rha III-GlcNAc-Rha I-Rha II-Rha III-GlcNAc-Rha I-Rha II. Acetylation of 0-2 of rhamnose III of the O-polysaccharide chain, either brought about by Sf6 lysogenization or found in wild-type S. flexneri (3b) strains, prevented enzymatic hydrolysis. O-deacetylation of the polysaccharide chain again made it susceptible to the S6f endorhamnosidase.

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Two of seven sucrose-fermenting Salmonella strains obtained from clinical sources were found capable of conjugal transfer of the sucrose fermentation (Scr+) property to the Escherichia coli K-12 strain WR3026. The genetic elements conferring this Scr+ property, designated scr-53 and scr-94, were then conjugally transmissible from E. coli WR3026 Scr+ exconjugants to other strains of E. coli at frequencies of 5 x 10-I to 5 x 10-I for the scr-53 element and 10 6 to 10-s for the scr-94 element. In E. coli hosts, both of these elements were compatible with F-lac and with each of six previously characterized transmissible lac elements. No antibiotic resistance characteristics or colicin production were discovered to be associated with either scr-53 or scr-94. Neither scr element generated a male host response to the female-specific phage XII, but the scr-53 element rendered its E. coli host sensitive to the male-specific phage R-17. E. coli hosts containing scr-53 were susceptible to lysis by Plvir, and transduction of the scr-53 element was accomplished with this phage. The scr-53 element was isolated from E. coli WR3026, Scr+ transductants, and E. coli WR2036 Scr+ exconjugants as a covalently closed circular deoxyribonucleic acid molecule with a molecular weight (determined by electron microscopy) of approximately 52 x 106. Receipt of the scr-94 element rendered E. coli hosts of this element unsusceptible to lysis by Plvir, although adsorption of the phage by an E. coli WR3026 exconjugant containing scr-94 occurred as efficiently as it did on WR3026 itself. Repeated examination of E. coli strains harboring scr-94, as well as of the Salmonella strain which initially contained it, did not reveal the presence of circular deoxyribonucleic acid. The synthesis of the sucrose cleaving enzyme was inducible in E. coli exconjugants containing either scr-53 or scr-94.

Neisseria gonorrhoeae strain GC82 contains a plasmid specifying a 8-lactamase (,3-Lam+}. Mixed incubation of strain GC82 with a penicillin-susceptible (X-Lam-), streptomycin-resistant mutant of strain GC9 results in the expression of f8-lactamase activity and streptomycin resistance in the transcipients. The frequency of transfer of the plasmid-specified resistance to penicillin seems to be proportional to the initial input ratio of the mating mixture of donor to recipient and to correlate positively with bacterial density. Cell-to-cell transmission of the deoxyribonucleic acid (DNA) appears to be by a conjugal mechanism or, alternatively, by an as yet undescribed transducing phage. Additionally, whole-cell DNA from a f8-lactamase-producing strain could be used to transform streptomycin-resistant recipients, resulting in the expression of both 8-lactamase activity and streptomycin resistance in the transformants, and purified gonococcal plasmid DNA transformed Escherichia coli but not the gonococcus. Circular DNA extracted from donor GC82 comprised three molecular species (approximately 2.7, 4.8, and 25 megadaltons [Mdal]), whereas the recipients GC9-S (Ste) contained only the 2.7-Mdal cryptic DNA species. DNA from the GC9-S82 (StrW, ,8-Lam+) transcipient contained a 4.8-Mdal species in addition to the cryptic molecular species (2.7 Mdal). The finding that the transcipient will not retransfer f8-lactamase is consistent with the hypothesis that the 25-Mdal plasmid promotes mobilization of the smaller 4.8-Mdal R plasmid.Although Neisseria gonorrhoeae has been traditionally thought of as a susceptible organism, the occurrence of gonococcal strains that are relatively resistant to penicillin and other antibiotics has gradually become an important clinical problem during the past 15 years, necessitating the use of elevated dosages of penicillin. It should be noted that there have been recent indications that the minimal inhibitory concentration (MIC) for penicillin of clinical isolates has decreased somewhat (24, 31).Resistance to penicillin in bacteria is frequently associated with the presence of 18-lactamase. The literature on 83-lactamase in gramnegative bacteria has been reviewed extensively (33). A number of these resistances have been specified by R plasmids. Previously, no /8-lactamase has been reported in N. gonorrhoeae, and resistance of the gonococcus was occasioned by a change in the binding site for penicillin (34). In the last several years the isolation of /3-lactamase-producing strains ofN. gonorrhoeae has been reported (1,2,5,28,30). Recent reports have indicated the presence of plasmid-specified, /8-lactamase-containing gonococci presumably associated with very high levels of resistance in these strains (13) and conjugal transfer of the gonococcal /8-lactamase plasmid (12).Evidence for plasmid deoxyribonucleic acid (DNA) in N. gonorrhoeae strain 2686 type 1 has been presented by Engelkirk and Schoenhard (14) and Maness and Sparling (24). The presence of plasmid DNA in each of the colonial types of...