Isolation of plasmid deoxyribonucleic acid from two strains of Bacteroides. (73/852)

Two clinical isolates of Bacteroides contained covalently closed circular deoxyribonucleic acid (DNA) as shown by sedimentation in an alkaline sucrose gradient, CsCl ethidium bromide equilibrium centrifugation, and electron microscopy. Bacteriodes fragilis N1175 contained a homogeneous species of plasmid DNA with a molecular weight of 25 x 10(6). Bacteroides ochraceus 2228 contained two distinct, covalently closed circular DNA elements. The larger cosedimented with the covalently closed circular DNA form of the R plasmid, R100, corresponding to a molecular weight of 70 x 10(6); the smaller sedimented as a 58S molecule with a calculated molecular weight of 25 x 10(6). The roles of these plasmids are unknown. Neither strain transferred antibiotic resistance to plasmid-negative Bacteroides or Escherichia coli, and neither produced bacteriocins active against other Bacteroides or sensitive indicator strains of E. coli.  (+info)

Sulfonamide resistance mechanism in Escherichia coli: R plasmids can determine sulfonamide-resistant dihydropteroate synthases. (74/852)

Several natural isolate E. coli strains highly resistant to sulfonamides and antibiotics are shown to contain a sulfonamide-resistant dihydropteroate synthase (2-amino-4-hydroxy-6-hydroxymethyl-7,8-dihydropteridine-diphosphate:4-aminobenzoa te 2-amino-4-hydroxydihydropteridine-6-methenyltransferase, EC 2.5.1.15) in addition to the normal sensitive enzyme. The resistant dihydropteroate synthases examined are determined by an R plasmid and are smaller and less heat stable than the normal sulfonamide-sensitive enzyme. One synthase resistant to any sulfonamide tested, and to sulfanilic and arsanilic acids, was still inhibited by several non-sulfonamide analogs of p-aminobenzoate. Citrobacter and Klebsiella pneumoniae strains also show similar mechanisms of sulfonamide resistance.  (+info)

Potential for in vivo acquisition of R plasmids by one strain of Vibrio cholerae biotype El tor. (75/852)

The feces of five patients admitted to a hospital during an outbreak of cholera in Melbourne, Australia, in November 1972, were examined for the presence of tetracycline-resistant coliforms and tetracycline-resistant strains of Vibrio cholerae. Despite the abundance of tetracycline-resistant coliforms able to transfer this resistance to other strains of Escherichia coli, no tetracycline-resistant strains of V. cholerae were detected. In vitro transfer experiments using the V. cholerae strain responsible for the outbreak as recipient revealed that it was a particularly poor host for most R plasmids.  (+info)

Distribution of R plasmids among the O-antigen types of Escherichia coli isolated from human and animal sources. (76/852)

The O-antigen types of 600 independently isolated Escherichia coli strains from human feces have been determined, and the types have been related to the antibiotic resistance patterns of the strains. The relative abundance of each O-antigen type differed in the susceptible and resistant series of strains. The majority (86%) of the resistant strains carried R plasmids. Resistant E. coli (20.3%) were found associated with O-antigen types 8, 9 and 101, whereas the susceptible strains covered a wide range of O-antigen types. Examination of 174 resistant strains isolated from calf feces also showed a prevalence of O-antigen types 8, 9, 101 (24.1%), and it seems probable that strains expressing these three O-antigen types commonly carry R plasmids in the alimentary tracts of man and calves. The number of strains not typeable with the O sera available were similar in the human (12.5%) and the calf (11.5%) series. There are no grounds for distinguishing "human" from "calf" E. coli on the basis of their O-antigen reactions.  (+info)

Plasmid-determined epistatic susceptibility to kasugamycin. (77/852)

The effect of two representative plasmids, R100 and F8-gal, on the susceptibility of Escherichia coli to kasugamycin was studied. R(+) and F(+) cells were found to be more susceptible to this antibiotic than R(-) and F(-) cells, respectively. Retransfer and curing experiments of these plasmids show that this increased susceptibility of host cells to kasugamycin was conferred by either of the plasmids. At the early stage of growth of R100(+) cells in the presence of kasugamycin, R(-) segregants overgrew the population and then they were replaced by kasugamycin-resistant mutants of the R(+) cells which became the majority cell line of the population. The former phenomenon is assumed to be due to the increased susceptibility of R100(+) cells to kasugamycin, and the latter is probably related to the finding that R100 enhances the spontaneous mutation of host cells to resistance to kasugamycin. The practical and experimental significance of these findings are discussed.  (+info)

Binding of bacteriocin Clo DF13 to Clo DF13 plasmid deoxyribonucleic acid in vivo and in vitro. (78/852)

The bacteriocinogenic plasmid Clo DF13 is present in Escherichia coli to the extent of 10 copies per cell. A complex of Clo DF13 plasmid deoxyribonucleic acid (DNA) and protein can be isolated from cells. Treatment of the complex with ionic detergents or proteases dissociates the complex but does not convert any supercoiled Clo DF13 DNA to the open circular form, indicating that this complex is not a relaxation complex. The complex is stable in 0.5 M NaCl and contains one polypeptide species. The protein, present in the complex, appeared to be bacteriocin Clo DF13 for the following reasons: (i) the protein is de novo synthesized in Clo DF13-harboring minicells, indicating that this protein is Clo DF13 specific; (ii) this protein shows bacteriocinogenic activity on a bacteriocin Clo DF13-susceptible indicator strain; (iii) this protein has the same molecular weight (60,000) as bacteriocin Clo DF13. DNA-protein binding experiments, involving QAE-Sephadex column chromatography and nitrocellulose membrane filters, demonstrate that bacteriocin Clo DF13 has also affinity in vitro for Clo DF13 DNA. Membrane filter binding experiments revealed that bacteriocin Clo DF13 does not interact with other DNA species, such as ColE1 DNA, yeast DNA, calf thymus DNA, phiX174 DNA, and also not with denatured Clo DF13 DNA. In addition no binding to Clo DF13 DNA of a related bacteriocin, colicin E3, could be detected. These results indicate that the binding of bacteriocin Clo DF 13 to double-stranded Clo DF13 DNA is very specific.  (+info)

Chromosome-plasmid interaction in Escherichia coli K-12 carrying a thermosensitive plasmid, Rts1, in autonomous and in integrated states. (79/852)

An Hfr strain of Escherichia coli K-12 was obtained by integrative suppression with a thermosensitive plasmid, Rts1. The R plasmid was integrated into the chromosome between rif and thr, and transfer of the chromosome occurred counterclockwise. The thermosensitivity of host cell growth due to the dnaA mutation was markedly but not completely reduced in this integratively suppressed Hfr strain. When the dnaA mutation was removed by transducing the dnaA+ genome to this Hfr, the thermosensitivity of cell growth due to existence of Rts1 was suppressed in contrast to strains carrying it autonomously. Thermosensitivity of cell growth appeared again when the plasmid was detached from the chromosome to exist autonomously. Contrary to the effect on cell growth, the transfer of the chromosome and the plasmid itself and the ability to "restrict" T-even phages were still thermosensitive in all of these strains carrying Rts1, irrespective of its state of existence. The detached plasmid as well as the original Rts1 were segregated upon growth at 42 C. These data are discussed in relation to chromosome-plasmid interaction. One of the most important conculusions is that some plasmid genes, related to their replication, are phenotypically suppressed by the chromosome when it is integrated.  (+info)

Relaxation complexes of plasmid DNA and protein. I. Strand-specific association of protein and DNA in the relaxed complexes of plasmids ColE1 and ColE2. (80/852)

The ColE1 and ColE2 relaxation complexes of supercoiled DNA and protein were purified from Escherichia coli cells. Protein remains associated with the open circular DNA of these complexes after induction of relaxation with sodium dodecyl sulfate. The protein is associated specifically with the strand that possesses a site-specific break in the Co1E1 and ColE2 relaxed complexes. This protein remains associated with the DNA after centrifugation of the relaxed complex in a neutral or alkaline (pH 12.5) cesium chloride gradient or treatment with 8 M urea, 2 M NaSCN, 2M LiCl, 0.2 M sodium acetate, pH 4.6, and 70% formamide at 60 degrees.  (+info)