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Biomedical subjects

R Williamson

Publications and source records attributed to R Williamson.

At least 271 records · Page 15Linked to original sources
PubMed1989

Inducible resistance to vancomycin in Enterococcus faecium D366.

Strain D366, a clinical isolate of Enterococcus faecium, is resistant (minimum inhibitory concentration [MIC] 32 mg/L) to vancomycin. When exponential-phase cultures were exposed to half the MIC of vancomycin, a lag of 3-4 h occurred before growth resumed. Cells preexposed to 1/2 MICs of vancomycin did not show any lag. Pregrowth of D366 with vancomycin caused resistance to all glycopeptides tested. Pregrowth in vancomycin resulted in synthesis of a 3.95-kDa cytoplasmic-membrane-associated protein. This protein was correlated with resistance in mutants with high-level resistance, in the presence of NaCl, which inhibited the activity of vancomycin, and when several glycopeptides with varying activities were tested. Vancomycin-grown cells appeared abnormal and lysed at a much slower rate than did normal cells. We conclude that (1) vancomycin resistance in D366 is inducible; (2) resistance is correlated with the synthesis of 39.5-kDa cytoplasmic membrane protein; and (3) this protein play an additional role in the inhibition of normal lytic functions.

Aged↗
PubMed1989

Inducible, transferable resistance to vancomycin in Enterococcus faecium, D399.

Enterococcus faecium D399 was isolated from the blood and peritoneal abscess of a patient with intraabdominal sepsis. The patient had not been treated with vancomycin, but the strain was found to be resistant with a MIC of 1000 mg/l. Resistance was inducible and transferable (probably by conjugation) to JH2-2, and correlated with induction of synthesis of a 39 kDa protein. This mechanism appears to be identical to that previously described for E. faecalis A256, suggesting that dissemination of this form of glycopeptide resistance has already occurred. The resistance phenotype of D399, however, differed somewhat from that found in other enterococcal strains with inducible resistance.

Drug Resistance, Microbial↗
PubMed1989

Gene mapping in cystic fibrosis and its clinical applications.

Current techniques in molecular genetics have permitted the localisation of the mutation causing cystic fibrosis to chromosome 7q31, and allowed isolation of very tightly linked markers. It is possible to offer early prenatal diagnosis, carrier testing, and alteration of risk of unaffected partners in most cases. However, community-wide definitive carrier testing and new methods of treatment await the isolation of the gene.

Chromosome Mapping↗
PubMed1989

Escherichia coli susceptible to glycopeptide antibiotics.

Mutants of Escherichia coli susceptible to vancomycin were isolated after mutagenesis with nitrosoguanidine. One such mutant was studied extensively. Multiple regression analysis of the relationship between physical properties of 20 glycopeptides and their in vitro activities against the vancomycin-susceptible mutant revealed a significant correlation with molecular mass (P = 0.007). pI, hydrophobicity, and affinity of the glycopeptide for the pentapeptide target were not as important for activity. This suggested that a block of access of the antibiotic to its target could be the major factor determining activity. Outer membrane proteins of the vancomycin-susceptible mutant, resistant parent, and revertant strains appeared normal. The mutant exhibited increased susceptibility to both erythromycin and fusidic acid which was lost in single-step revertants to vancomycin resistance. Polymyxin B nonapeptide was synergistic with erythromycin and fusidic acid against the parent and revertant but not against the susceptible mutant. Analysis of the susceptibilities of control strains of E. coli and Salmonella typhimurium with known defects in lipopolysaccharide (LPS) synthesis revealed that core LPS mutants (Re chemotype) were phenotypically similar to the E. coli mutant under study. However, the LPS core of the mutant migrated slightly less rapidly on sodium dodecyl sulfate-polyacrylamide gel electrophoresis than wild-type or revertant core LPS and did not resemble Re chemotype LPS core obtained from Salmonella rfaC and rfaD mutants. These data suggest that defects in LPS core structure other than loss of heptose moieties may also be important in loss of resistance to large, hydrophilic molecules such as glycopeptides.

Anti-Bacterial Agents↗
PubMed1989

Inducible, transferable resistance to vancomycin in Enterococcus faecalis A256.

A strain of Enterococcus faecalis (A256) was isolated from the urine of a patient with urinary sepsis and was found to exhibit susceptibilities (micrograms per milliliter) to various glycopeptides as follows: vancomycin, 256; teicoplanin, 16; 62208, 512; 62211, 4; and 62476, 16. As judged by growth rates before and after exposure to sub-MICs of glycopeptides, vancomycin and 62476 induced self-resistance, 62208 and 62211 induced slight self-resistance, and teicoplanin did not induce self-resistance. Vancomycin induced cross-resistance to all other glycopeptides tested, as judged both in growth experiments and by direct measurement of inhibition of peptidoglycan synthesis in cells exposed to sub-MICs of vancomycin. Thus, the spectra of activity of the glycopeptides were not correlated with their patterns of induction. There was a correlation between the increased synthesis of a 39-kilodalton (kDa) protein located in the cytoplasmic membrane and the induction of resistance. Protoplasts of A256 were susceptible to inhibition of peptidoglycan synthesis by vancomycin at levels similar to those for susceptible strains. Vancomycin resistance was transferable on filters from the parent strain to E. faecalis JH2-2 at a frequency of about 10(-7), and the 39-kDa protein was also inducible by glycopeptides in these transconjugants. We conclude that A256 is resistant to glycopeptides by virtue of the synthesis of a 39-kDa cytoplasmic membrane protein, that this protein is probably involved in preventing access of the glycopeptides to their peptidoglycan targets, and that this resistance is transferable, probably by conjugation.

Bacterial Outer Membrane Proteins↗
PubMed1989

Isolation of a new DNA marker in linkage disequilibrium with cystic fibrosis, situated between J3.11 (D7S8) and IRP.

A cosmid library of recombinants containing nonmethylated CpG sites for rare-cutter restriction enzymes was used previously to isolate the gene IRP and four polymorphic DNA markers (pPT-3, pXV-2c, pCS.7, and pKM.19) which are close to and in linkage disequilibrium with the cystic fibrosis (CF) mutation. We have analyzed several new clones from the same library and have isolated a further cosmid, cNX.6d, which maps approximately 160 kb from CS.7, in the J3.11 direction. A DNA fragment (pMP6d-9) (D7S399) derived from cosmid cNX.6d detects a frequent polymorphism with MspI. Strong linkage disequilibrium between CF and MP6d-9 is found in European populations. Recombinations in two families suggest that CF is between the MspI polymorphic site recognized by pMP6d-9 and the polymorphism recognized by pJ3.11. The new marker is the closest, to date, to CF and will be useful for prenatal diagnosis and carrier testing.

Chromosome Mapping↗
PubMed1989

Molecular genetics and the transformation of clinical chemistry.

Clinical chemistry is going through an identity crisis, squeezed between automation (de-skilling) on the service side and molecular genetics in research. Automated routine estimations are now carried out and interpreted by machines; the skilled staff members required are more likely to have degrees in electronics than medicine or biochemistry. The role of molecular genetics is more ambiguous; it is inherently reductionist, in that it attempts to explain most clinical phenomena in terms of DNA sequence alone. This has been remarkably successful for single-gene defects (such as those causing Duchenne muscular dystrophy, hemoglobinopathies, cystic fibrosis, and ataxias) and may well prove equally so for Alzheimer's disease, cancer, heart disease, and schizophrenia. DNA diagnosis is not yet routine, but because of technical advances such as gene amplification ("PCR") and high-sensitivity gene-detection assays, it may soon become so, not only in major centers but also in local pathology laboratories and general practice. Clinical chemists must decide whether they wish to respond to this new and stimulating challenge by retooling and retraining. Should anyone be permitted into clinical chemistry during the 1990s without knowledge of both electronics and molecular genetics? Will there be a clinical chemistry in the twenty-first century other than through molecular genetics? This article is a personal response to these questions.

Base Sequence↗
PubMed1988

Mapping of mutation causing Friedreich's ataxia to human chromosome 9.

Friedreich's ataxia is an autosomal recessive disease with progressive degeneration of the central and peripheral nervous system. The biochemical abnormality underlying the disorder has not been identified. Prompted by the success in localizing the mutations causing Duchenne muscular dystrophy, Huntington's disease and cystic fibrosis, we have undertaken molecular genetic linkage studies to determine the chromosomal site of the Friedreich's ataxia mutation as an initial step towards the isolation and characterization of the defective gene. We report the assignment of the gene mutation for this disorder to chromosome 9p22-CEN by genetic linkage to an anonymous DNA marker MCT112 and the interferon-beta gene probe. In contrast to the clinical variation seen for the disorder, no evidence of genetic heterogeneity is observed.

Chromosome Mapping↗
PubMed1988

Simple non-invasive method to obtain DNA for gene analysis.

A technique is described which demonstrates that sufficient human DNA for direct gene analysis can be isolated from buccal epithelial cells obtained by mouthwash. This procedure is much simpler and cheaper than existing methods and, combined with DNA amplification by polymerase chain reaction, should allow community screening for carrier status for single gene defects such as cystic fibrosis.

Cheek↗