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Biomedical subjects

M H Richmond

Publications and source records attributed to M H Richmond.

At least 19 recordsLinked to original sources
PubMed1982

Penicillinase-producing Neisseria gonorrhoeae: a molecular comparison of 5.3-kb and 7.4-kb beta-lactamase plasmids.

Restriction endonuclease analysis and heteroduplex studies indicate that the only difference between the 5.3-kilobase (kb) and 7.4-kb plasmids from beta-lactamase-producing Neisseria gonorrhoeae is that the latter is the 5.3-kb plasmid with a 2.1-kb insertion. The insertion is bounded by inverted repeats of approximately 300 base pairs. Several plasmids from beta-lactamase-producing N. gonorrhoeae isolated at different times and in different countries were compared. Nine 5.3-kb plasmids were examined and found to be indistinguishable, as were sixteen 7.4-kb plasmids.

Base Sequence↗
PubMed1981

The tnpR gene product of TnA is required for transposition immunity.

A mutant of TnA no longer recognizing immune plasmids had been isolated. The mutation is complemented in trans by a functional tnpR gene. The requirement for wild type tnpR gene product for the establishment of transposition immunity was confirmed by the use of a derivative of transposon Tn3 in which both the tnpA and the tnpR genes are partly deleted. This deleted Tn3 was shown to transpose onto an immune plasmid in the presence of a wild type tnpA gene but not in the presence of both tnpA and tnpR genes.

DNA Transposable Elements↗
PubMed1980

Nucleotide sequences at the ends of the mercury resistance transposon, Tn501.

The nucleotide sequences at the ends of the mercury-resistance transposon, Tn501, have been determined. The terminal sequences are inverted repeated sequences 38 nucleotide pairs in length, which differ in 3 nucleotide pairs. The transposon is flanked by directly repeated sequences of 5 nucleotide pairs, originating from a single pentanucleotide sequence in the recipient replicon. There is no obvious homology between recipient replicons at the site of insertion of the transposon. The structures of the ends of Tn501 are compared with those of other transposons and insertion sequences. The use of Tn501 to locate an EcoRI site within a genetically defined sequence of interest is discussed.

Base Sequence↗
PubMed1980

Persistence and spread of a chloramphenicol resistance-mediating plasmid in antigenic types of Escherichia coli, pathogenic for piglets.

All chloramphenicol-resistant Escherichia coli strains isolated from piglets in the State veterinary Serum Laboratory, Copenhagen, in 1974-1975 harbored plasmids of IncFII group with largely the same resistance markers. Two strains from 1978 carried plasmids with similar characters. Restriction enzyme analysis of DNA from these plasmids with restriction endonucleases EcoRI, BglII, and PstI shows that the Cm plasmids are extremely closely related; but the patterns obtained (particularly from PstI digests) enable the classification of the plasmids into groups. These bear a strong relation to time and place of isolation so that plasmids isolated on the same farm belong to the same group even when their host strains are of different antigenic types. It is concluded that these plasmids have evolved from a single plasmid.

Animals↗
PubMed1979

'Cells' and 'organisms' as a habitat for DNA.

Although the bulk of the hereditary information in bacteria is organized as a single chromosome, it has been known for some years now that bacteria may also carry pieces of self-replicating extrachromosomal DNA. These units are known as plasmids. Sometimes such plasmids carry the information necessary to give rise to mature bacterial viruses under appropriate conditions, but in other cases they specify the production of enzymes and other proteins which alter the bacterial phenotype. Plasmids are often inessential for survival of bacteria, although they may widen the range of environmental conditions under which they flourish. Thus plasmids may be thought of as adventitious additions to the genetic content of bacterial cells. Recently it has become clear that furthur organizational units of DNA are to be found in bacterial cells. These units are called insertion sequences and transposons. Unlike plasmids and the chromosome, however, these DNA units do not carry enough genetic information to specify their own independent replication: they must rely on plasmids or the chromosome for that purpose. Nevertheless they behave in many respects as independent functional units. Although it is possible to think of the chromosome, plasmids and transposons/insertion sequences as three distinct hierarchies of bacterial DNA, genes may move from one hierarchy to another; and such transitions have important implications for the evolution of bacterial populations. Moreover, their study in bacteria may throw much light on the type of DNA interactions occurring in higher cells.

Base Sequence↗
PubMed1979

Persistence of plasmid-carrying tetracycline-resistant Escherichia coli in a married couple, one of whom was receiving antibiotics.

This paper describes an extension to an earlier account of the coliform flora carried by a married couple, one of whom was taking tetracycline for prolonged periods. The latter phase of this study was notable for the following: first, certain tetracycline-resistant Escherichia coli O antigen types persisted in one of the participants for several weeks after tetracycline was withdrawn; second, a course of ampicillin led to replacement of the tetracycline-resistant flora by one that was ampicillin resistant, but the end of the ampicillin course led to the reappearance of the tetracycline-resistant line, even though no tetracycline was being taken; and third, the tetracycline-sensitive O75 E. coli, which appeared toward the end of the survey, had not lost their plasmid but carried a derivative in which the tetracycline resistance gene(s) had been inactivated by the insertion of an extra piece of deoxyribonucleic acid with a molecular weight of about 1 megadalton.

Antigens, Bacterial↗
PubMed1979

Adhesion of commensal bacteria to the large intestine wall in humans.

Biopsies taken during colonoscopic examination of the human large bowel were used to examine the relationship of the commensal bacterial to the mucosal epithelial cell surface. Bacteria were seen adhering to the exposed epithelial cell surface and also to the mucus sheet. Isolation of aerobic organisms showed that Escherichia coli are closely associated with the gut wall throughout the large intestine. One strain of E. coli predominated in each biopsy, and this strain was present along the whole length of bowel. Adhesion of bacteria to the gut wall does occur in vivo and may be one of the factors involved in the ability of an organism to colonize and persist.

Escherichia coli↗