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P Guerry

Publications and source records attributed to P Guerry.

62 records · Page 4Linked to original sources
PubMed1974

Molecular nature of two nonconjugative plasmids carrying drug resistance genes.

Two nonconjugative R-plasmids, N-SuSm and N-Tc, have been characterized. Both were of relatively small size (5 x 10(6) to 6 x 10(6) daltons) and present in multiple copies within their respective bacterial hosts. N-SuSm possessed a guanine plus cytosine content of 55%, whereas N-Tc was 49% guanine plus cytosine. Although these plasmids were inherently nontransmissible they could be mobilized by a large variety of transfer agents including Ent, Hly, and K88. The fi(-) transfer factors tested were far more likely (about 200x) to mobilize these nonconjugative plasmids than were the fi(+) transfer factors tested. Although the mobilization phenomenon was not found to be associated with a detectable level of direct stable recombinational union between N-SuSm or N-Tc with a transfer factor, we were able to demonstrate a low level of recombination between these replicons and a transfer factor by P1-mediated transduction. The isolation of recombinants between transfer factors and nonconjugative plasmids presumably represents one means by which unitary molecular types of R-plasmids arise and by which existing R-plasmids may acquire new resistance determinants.

Carbon Radioisotopes↗
PubMed1974

Extrachromosomal elements in group N streptococci.

The deoxyribonucleic acid (DNA) of Streptococcus lactis C2, S. cremoris B(1), and S. diacetilactis 18-16 was labeled by growing cells in Trypticase soy broth containing (3)H-labeled thymine. The cells were gently lysed with lysozyme, ethylenediaminetetraacetic acid, and sodium lauryl sulfate. The chromosomal DNA was separated from plasmid DNA by precipitation with 1.0 M sodium chloride. The existence of covalently closed circular DNA in the three organisms was shown by cesium chloride-ethidium bromide equilibrium density gradient centrifugation of the cleared lysate material. In an attempt to correlate the loss of lactose metabolism with the loss of plasmid DNA, lactose-negative mutants of these organisms were examined for the presence of extrachromosomal particles. Covalently closed circular DNA was detected in the lactose-negative mutants of S. lactis C2 and S. diacetilactis 18-16. In S. cremoris B(1), however, no covalently closed circular DNA was observed by using cesium chloride-ethidium bromide gradients. Electron micrographs of the satellite band material from S. lactis C2 and its lactose-negative mutant confirmed the presence of plasmid DNA. Three distinct plasmids having approximate molecular weights of 1.3 x 10(6), 2.1 x 10(6), and 5.1 x 10(6) were observed in both organisms.

Centrifugation, Density Gradient↗
PubMed1974

R62, a naturally occurring hybrid R plasmid.

R62, a naturally occurring R factor, was shown to be a single deoxyribonucleic acid molecule composed of polynucleotide sequences typical of I group plasmids and also sequences typical of the N group. It determined I pili and belonged to the Ialpha compatibility group. Although compatible with plasmids of group N, R62 showed complex genetic reactions with N plasmids which are described and interpreted. It is concluded that R62 was the product of illegitimate recombination between an I group and an N group plasmid.

Ampicillin↗
PubMed1973

General method for the isolation of plasmid deoxyribonucleic acid.

Plasmid deoxyribonucleic acid (DNA) ranging from 5 x 10(6) to 65 x 10(6) daltons may be isolated from chromosomal DNA by the preferential precipitation of the higher-molecular-weight chromosomal DNA in the presence of sodium lauryl sulfate and a high concentration of NaCl.

Centrifugation↗