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Biomedical subjects

D B Clewell

Publications and source records attributed to D B Clewell.

At least 145 records · Page 8Linked to original sources
PubMed1979

Plasmid-related transmissibility and multiple drug resistance in Streptococcus faecalis subsp. zymogenes strain DS16.

Streptococcus faecalis subsp. zymogenes strain DS16 was found to harbor two plasmids, designated pAD1 (35 megadaltons) and pAD2 (15 megadaltons). pAD1 is transmissible and determines a hemolysin-bacteriocin, whereas pAD2 is non-conjugative and determines resistance to erythromycin, streptomycin, and kanamycin. pAD2 could be mobilized by pAD1, but usually involved formation of a pAD1-pAD2 cointegrate.

Conjugation, Genetic↗
PubMed1978

Induced cell aggregation and mating in Streptococcus faecalis: evidence for a bacterial sex pheromone.

Recipient strains of Streptococcus faecalis produce a trypsin sensitive, heat resistant, nuclease resistant factor, designated clumping-inducing agent (CIA) which causes strains carrying certain conjugative plasmids to aggregate. RNA and protein synthesis but not DNA synthesis are required for aggregation to occur. Recipient filtrates that contain CIA activity also induce donors to mate at high frequencies. Introduction of a transferable plasmid into strains producing CIA dramatically reduces the amount of CIA activity produced by the strain but allows the strain to respond to exogenously added CIA. Our data suggest that CIA represents a bacterial sex hormone (pheromone).

Animals↗
PubMed1978

Characterization of a small plasmid determining resistance to erythromycin, lincomycin, and vernamycin Balpha in a strain of Streptococcus sanguis isolated from dental plaque.

A plasmid determining resistance to erythromycin (inducible), lincomycin, and vernamycin B(alpha) was isolated from a strain of Streptococcus sanguis isolated from dental plaque of a patient who had been on erythromycin therapy for an extended period of time. The plasmid, designated pAM77, had a molecular weight of 4.5 x 10(6) and was present to the extent of one to two copies per bacterial chromosome. The plasmid could transform S. sanguis strain Challis.

Anti-Bacterial Agents↗
PubMed1977

Identification and characterization of a small sequence located at two sites on the amplifiable tetracycline resistance plasmid pAMalpha1 in Streptococcus faecalis.

Streptococcus faecalis DT-11 harbors the 6.0-megadalton plasmid pAMalpha1, which determines resistance to tetracycline (TC). When this strain is grown in the presence of TC for a number of generations, a reversible gene amplification occurs, generating tandem repeats of a 2.65-megadalton segment of the plasmid. On the basis of heteroduplex studies between various forms of pAMalpha1 and fragments generated by the Escherichia coli restriction endonuclease EcoRI, we have obtained direct evidence for the presence of a small sequence designated RS1 (for recombination sequence) located on both sides of the TC resistance determinant. Corresponding points on the two sequences are separated by 2.65 megadaltons of deoxyribonucleic acid. The two RS1 sequences have the same polarity and are of a size corresponding to about 380 nucleotide base pairs. The data presented serve as strong support for amplification models that are based on recombinational events involving the RS1 sequences.

Base Sequence↗
PubMed1977

Analysis of plasmid deoxyribonucleic acid in a cariogenic strain of Streptococcus faecalis: an approach to identifying genetic determinants on cryptic plasmids.

Streptococcus faecalis strains ND539 and OG1 have been previously shown to be cariogenic in gnotobiotic animals. Deoxyribonucleic acid analyses have revealed the presence of a single 26-megadalton plasmid designated pAM539 in the former strain, whereas the latter strain was found to be plasmid-free. By gene transfer experiments, it was possible to construct isogenic pairs of strains that differed only with regard to the presence or absence of pAM539. Comparative studies of isogenic pairs showed that the presence of pAM539 conferred bacterial sensitivity to a bacteriocin produced by S. faecalis strain 5952.

Animals↗
PubMed1977

Characterization of plasmids determining hemolysin and bacteriocin production in Streptococcus faecalis 5952.

Two plasmids designated pOB1 and pOB2 were isolated from Streptococcus faecalis strain 5952 and found to have molecular weights of approximately 46 X 10(6) and 28 X 10(6), respectively. pOB1 was found to determine hemolytic activity and was transmissible, whereas pOB2 appeared to determine a bacteriocin that is specifically inhibitory to S. faecalis strains harboring the 26-megadalton plasmid pAM539.

Bacteriocins↗
PubMed1975

Plasmid-determined tetracycline resistance in Streptococcus faecalis: evidence for gene amplification during growth in presence of tetracycline.

The tetracycline (TG)-resistant Streptococcus faecalis strain DS-5Cl harbors two plasmids designated alpha and gamma with molecular masses of approximately 6 and 35 million daltons, respectively. TC-sensitive variants were derived by storing cells at 45 degrees for 2-3 weeks. Analysis of covalently closed circular DNA from five such variants (derived independently) revealed that in each variant the alpha-plasmid, which normally sediments at 28 S (supercoiled) in a sucrose density gradient, was replaced by a 22S substance. Growth of DS-5Cl in the presence of 150 mug/ml of TC (minimum inhibitory concentration is 250 mug/ml in liquid broth) for a prolonged period of time (50-60 generations) resulted in the disappearance of 28S DNA and the appearance of a heterogeneous covalently-closed circular DNA sedimenting at about 40-48 S. This phenomenon was accompanied by an increase in the level of bacterial TC-resistance, whereby tells were subsequently grown in the absence of TC for 70-80 generations, the heterogeneous DNA disappeared and a typical 28S alpha-plasmid reappeared. The cells also became less resistant to TC, i.e., the minimum inhibitory concentration returned to 250 mug/ml. These data suggest that bacterial growth in the presence of TC results in a reversible gene amplification with respect to a TC-resistant determinant residing on the alpha-plasmid.

Cell Division↗
PubMed1975

Plasmid-determined resistance to erythromycin: comparison of strains of streptococcus faecalis and streptococcus pyogenes with regard to plasmid hmology and resistance inducibility.

Streptococcus faecalis strains DS-5 and Streptococcus pyogenes strain AC-1 both have a 17 million dalton plasmid that determines resistance to erythromycin, lincomycin, and vernamycin B(alpha). The results of deoxyribonucleic acid-deoxyribonucleic acid hybridization experiments indicate that the two plasmids are about 95% homologous. It was also shown that erythromycin resistance is inducible in AC-1 and constitutive in DS-5.

Drug Resistance, Microbial↗
PubMed1975

Transmissible toxin (hemolysin) plasmid in Streptococcus faecalis and its mobilization of a noninfectious drug resistance plasmid.

Streptococcus faecalis strain DS-5 has been shown previously to contain three plasmids, pAMalpha1, pAMbeta1, and pAMgamma1. Mixed incubation of DS-5 with strain JH2-2, a plasmid-free S. faecalis recipient, results in the transfer of pAMalpha1 (which determines resistance to tetracycline) and/or pAMgamma1. Analyses of recipients carrying various combinations of these plasmids have revealed the pAMgamma1 codes for toxin (hemolysin) production and two bacteriocin activities. JH2-2 strains carrying both pAMalpha1 and pAMgamma1, or pAMgamma1 only, can donate their plasmids to other recipients, whereas strains carrying only pAMalpha1 cannot serve as donors. This indicates that pAMgamma1 actually mobilizes the otherwise nontransferable pAMalpha1.

Bacteriocins↗
PubMed1974

Characterization of three plasmid deoxyribonucleic acid molecules in a strain of Streptococcus faecalis: identification of a plasmid determining erythromycin resistance.

Three plasmids designated alpha, beta, and gamma, distinguishable by their molecular weights (6, 17, and 34 million, respectively) were isolated from Streptococcus faecalis strain DS-5 (ATCC 14508). Derivatives of this strain "cured" for erythromycin resistance lacked the beta-plasmid. In the parent strain the beta-plasmid was estimated to be present to the extent of one to two copies per chromosomal genome equivalent whereas the alpha- and gamma-plasmids were about nine and five copies, respectively.

Acridines↗
PubMed1972

Isolation of supercoiled colicinogenic factor E 1 DNA sensitive to ribonuclease and alkali.

The synthesis of the covalently-closed, circular DNA form of colicinogenic factor E(1) (ColE(1)) continues in Escherichia coli cells after the addition of chloramphenicol. A large portion of the purified supercoiled ColE(1) DNA molecules made in the presence of chloramphenicol are converted to the open circular DNA form after treatment with alkali (pH 13), RNase A, or RNase H. These treatments do not significantly affect the covalently-closed form of ColE(1) DNA isolated from normally growing E. coli cells. The open circular product resulting from treatment of supercoiled ColE(1) DNA with RNase A possesses a single break in one strand of the circular duplex. The site sensitive to RNase A occurs with equal probability in either of the complementary strands. Both synthesis of ColE(1) DNA and the formation of supercoiled ColE(1) DNA sensitive to RNase A or alkali are prevented by the inhibitor of RNA synthesis, rifampicin. These results indicate that covalently-closed ColE(1) DNA containing one or more ribonucleotides accumulates during ColE(1) replication in the presence of chloramphenicol. It is proposed that this incorporated RNA served as a primer during the initiation of synthesis of ColE(1) DNA and that its removal from the circular DNA is inhibited in cells incubated in the presence of chloramphenicol.

Carbon Isotopes↗