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J F Richardson

Publications and source records attributed to J F Richardson.

At least 19 recordsLinked to original sources
PubMed2001

Stacking efficiency of diselenadiazolyl pi-dimers. Consequences for electronic structure and transport properties.

The preparation and crystal structure of 5-cyanofuran-2-[1,2,3,5-diselenadiazolyl], [RCN(2)Se(2)] (R = 5-cyanofuran), is reported. Crystal data for C(6)H(2)ON(3)Se(2): monoclinic, space group P2(1), a = 7.1121(7), b= 20.541(2), c =20.923(2) A, beta = 99.785(1) degrees, Z = 16. The crystal structure consists of diselenadiazolyl pi-dimer stacks running parallel to the x direction; the asymmetric unit consists of four pi-dimer units. The dimers are aligned into snakelike ribbons along the y direction, with consecutive dimers linked by head-to-tail CN-Se contacts. Each pi-dimer stack is bordered by two out-of-register stacks, but most interstack Se-Se contacts lie outside the van der Waals separation. Along the pi-dimer stacks, the intradimer Se-Se distances range from 3.183(10) to 3.294(1) A, and the interdimer Se-Se distances range from 3.826(1) to 3.945(1) A. Like other pi-dimer stacked diselenadiazolyls, [C(6)H(2)ON(3)Se(2)](2) is diamagnetic over the temperature range 4-380K. Variable temperature single-crystal conductivity measurements reveal a room-temperature conductivity near 10(-5) S cm(-1) and provide a calculated band gap of 0.72 eV. The structural results and transport properties are interpreted in the light of Extended Hückel band structure calculations.

Journal Article↗
PubMed2001

Strong supramolecular-based magnetic exchange in pi-stacked radicals. Structure and magnetism of a hydrogen-bonded verdazyl radical:hydroquinone molecular solid.

The X-ray crystal structure and magnetic properties of a molecular crystal consisting of 1,5-dimethyl-3-(2-pyridyl)-6-oxoverdazyl radical and hydroquinone (pyvd:hq) are presented. The structure contains a two-dimensional network of hydrogen bonds involving the hydroquinones and the pyridine ring of the pyvd radical. The radicals adopt an unusual head-over-tail (antiparallel) pi-stacked array perpendicular to the hydrogen-bonded planes. The variable-temperature magnetic susceptibility data can be modeled using a one-dimensional antiferromagnetic chain model, with J = -58 cm(-1). The strength of the magnetic coupling is very unusual because there are no close intermolecular radical-radical contacts to provide conventional pathways for magnetic interactions. A pathway for coupling is proposed involving the mediation of magnetic exchange interactions between radical centers by the pyridine rings. Density functional calculations on the pyvd radical, as well as aggregates thereof based on the X-ray structure, have been employed in attempts to understand the possible mechanisms by which the strong magnetic interactions are achieved.

Journal Article↗
PubMed2001

Coinfection with Campylobacter species: an epidemiological problem?

AIMS: To determine the frequency of coinfection with multiple strains in sporadic cases of human Campylobacter infection. METHOD AND RESULTS: During 1999 10 single colonies of Campylobacter were cultured from each of 53 positive faecal samples. Five isolates were taken from nonselective agar after passive filtration of faecal suspensions and five isolates were taken from selective agar plates. All isolates were sero- and phage typed and their antibiotic resistance determined. Pulsed-field gel electrophoresis and flagellin gene typing were performed on selected isolates. One patient was infected with Camp. coli, the remainder with strains of Camp. jejuni. The majority of patients was infected with a single strain of Campylobacter, but from each of four samples, 7.5%, two strains of Camp. jejuni, confirmed by molecular typing, were identified. CONCLUSION: Coinfection occurs in sporadic cases of campylobacteriosis. SIGNIFICANCE AND IMPACT OF THE STUDY: This study has implications in outbreak investigation when distinct strains have been isolated from epidemiologically related patients and/or the suspected source or vehicle.

Adult↗
PubMed1999

Use of fluorescent amplified fragment length polymorphism (fAELP) to characterise methicillin-resistant Staphylococcus aureus.

The new PCR-based genotyping technique, fluorescent amplified fragment length polymorphism (fAFLP), was compared for discriminatory power and reproducibility with standard phenotypic methods, a coagulase gene (coa) restriction fragment length polymorphism (RFLP) method and pulsed-field gel electrophoresis (PFGE), in typing 34 isolates and four reference strains of methicillin-resistant Staphylococcus aureus (MRSA). The fAFLP showed from 40 to 75 fragments, 50 to 450 base pairs (bp) in size. Based on replicate studies, the isolates were judged indistinguishable when their fAFLP pattern was >93.7% similar. Only two of the isolates were indistinguishable by this criterion. Thirty-one MRSA fell into four major fAFLP groups (1, 2, 3 and 4) at the level of >79.9% similarity. Three other isolates and an EMRSA-16 strain fell outside these major groups. Within both fAFLP groups 1 and 2, two subgroups, A and B, could be identified at approximately 82.0% similarity. While most isolates within group 1 could also be separated by their phenotypic and coagulase gene (coa) RFLP pattern, all the isolates within fAFLP groups 2A and 2B were identical on the basis of these characters. The MRSA within fAFLP groups 3 and 4 were heterogeneous by their phenotypic characteristics and coa gene RFLP patterns. fAFLP was reproducible and distinguished between MRSA isolates that appeared identical by other methods. It is likely to contribute to the epidemiological analysis of outbreaks of MRSA infection.

Coagulase↗
PubMed1999

Phages for methicillin-resistant Staphylococcus aureus: an international trial.

An internationally agreed and validated set of phages is used worldwide for the typing of strains of Staphylococcus aureus of human origin. However, because of the sometimes reduced susceptibility of methicillin-resistant strains (MRSA) to these phages, some of the national typing centres use locally isolated and characterized sets of experimental phages. In this trial, 42 such phages were distributed to 6 centres and tested against 744 isolates of MRSA with the intention of defining a phage set to augment the international set. The use of these experimental phages increased the percentage typability from 75% with the international set to 93% and the number of identifiable lytic patterns from 192 to 424. A subset of 10 experimental phages was selected. When this subset was compared with the experimental panel, the typability rate was 91% and 370 distinct patterns were obtained. This subset of phages has been distributed for international trial.

Bacteriophage Typing↗
PubMed1999

PCR-RFLP analysis of the coagulase gene of Staphylococcus aureus: application to the differentiation of epidemic and sporadic methicillin-resistant strains.

Preventing cross-infection with epidemic strains of methicillin-resistant Staphylococcus aureus (MRSA) requires effective control measures. These call for simple, rapid, discriminatory and reproducible methods for typing this pathogen. In this study 140 isolates/strains from 105 hospitals in England and Wales, representing 72 diverse phage types, were analysed by bacteriophage typing and PCR coagulase (coa) gene restriction fragment length polymorphism (RFLP). Isolates gave a coa gene PCR product that was either 660 base pairs (bp), 603 bp or 547 pb in size. The PCR products were digested with Alu I and Cfo I, and the fragments separated by gel electrophoresis. Eight coa gene RFLP patterns, numbered 1 to 8, were observed. Pattern 3 was most common (N = 25 isolates), followed by patterns 2 and 5 (18 isolates each), pattern 1 (14 isolates), pattern 4 (11 isolates), pattern 7 (10 isolates), pattern 8 (eight isolates) and pattern 6 (six isolates). Isolates of the same phage type often gave different coa gene RFLP patterns, and the patterns within the epidemic types EMRSA-03, EMRSA-15 and EMRSA-16 were heterogeneous. Thus, representatives of EMRSA-03 were subtyped to coa RFLP patterns 1 and 2, those of EMRSA-05 to coa RFLP patterns 1, 2, 7 and 8, and those for EMRSA-16 to coa RFLP patterns 2, 3, 4, 5 and 6. The range of patterns within single phage types of S. aureus could help to discriminate between isolates/strains, and in a hierarchical approach coa gene RFLP could occupy an intermediate position between phage typing and pulsed-field gel electrophoresis (PFGE).

Bacteriophage Typing↗
PubMed1998

Molecular typing of Staphylococcus aureus based on PCR restriction fragment length polymorphism and DNA sequence analysis of the coagulase gene.

A typing procedure for Staphylococcus aureus was developed based on improved PCR amplification of the coagulase gene and restriction fragment length polymorphism (RFLP) analysis of the product. All coagulase-positive staphylococci produced a single PCR amplification product of either 875, 660, 603, or 547 bp. Those strains of epidemic methicillin-resistant S. aureus 16 (EMRSA-16) studied all gave a product of 547 bp. PCR products were digested with AluI and CfoI, and the fragments were separated by gel electrophoresis. Ten distinct RFLP patterns were found among 85 isolates of methicillin-resistant S. aureus (MRSA) and 10 propagating strains (PS) of methicillin-sensitive S. aureus (MSSA) examined. RFLP patterns 1, 2, and 3 were specific to strains of EMRSA-3, -15, and -16, respectively. By contrast, RFLP patterns 4 and 5 were seen with a heterogeneous collection of strains, together with drug-resistant forms of S. aureus isolated in Europe and four propagating strains used for the international phage set. RFLP pattern 6 was given by the Airedale isolate and PS 95. RFLP pattern 7 encompassed EMRSA-2 (isolate 331), PS 94, and PS 96. An isolate from Germany gave RFLP pattern 8. Eight strains of MSSA gave patterns similar to those of methicillin-resistant strains (RFLP patterns 3, 4, 5, 6, and 7), but two, PS 42E and PS 71, gave unique RFLP patterns 9 and 10, respectively. The coagulase gene PCR products for 24 isolates of MRSA and two isolates of MSSA were sequenced for both strands. The sequences were aligned, and evolutionary lineages were inferred based on pairwise distances between isolates.

Bacterial Typing Techniques↗
PubMed1997

Epidemiological typing of coagulase-negative staphylococci from nosocomial infections.

Biotyping, antibiograms, bacteriophage typing, plasmid profile analysis and SDS-PAGE protein profiles were used to determine the relatedness of 44 Staphylococcus epidermidis and four S. haemolyticus isolates from 14 patients. A selection of these were further characterised by ribotyping. Biotyping classified the isolates into three major groups but was considered a poor strain marker. Although antibiograms classified the S. epidermidis isolates into 20 groups, some changes in the susceptibility patterns of related isolates from a single patient were demonstrated. Bacteriophage typing was the least discriminatory of the methods used. SDS-PAGE gave highly related patterns for the majority of S. epidermidis isolates. Plasmid profile analysis and ribotyping, with a minimum of two restriction endonucleases, were the most discriminatory methods for typing S. epidermidis. Nonetheless, some isolates from the same patient - probably representing a single strain - varied in plasmid profile indicating plasmid instability. One of six related isolates from a single patient lacked two bands from the ribotyping pattern of the other isolates. Although no single method proved entirely satisfactory on all occasions, the combination of typing methods was sufficient to provide evidence of the relatedness of S. epidermidis isolates from individual patients.

Adult↗
PubMed1997

Comparison and application of ribosome spacer DNA amplicon polymorphisms and pulsed-field gel electrophoresis for differentiation of methicillin-resistant Staphylococcus aureus strains.

Analysis of sequences in the fragments of the 16S-23S rRNA intergenic spacer region by the ribosome spacer PCR (RS-PCR) can differentiate strains of methicillin-resistant Staphylococcus aureus (MRSA). We compared this technique with pulsed-field gel electrophoresis (PFGE) for typing MRSA strains and its application during an investigation of an outbreak. A total of 180 isolates of MRSA collected from various hospital laboratories within the United Kingdom and elsewhere were typed by PFGE and RS-PCR. PFGE identified 17 different types among the 180 strains examined, and RS-PCR generated 13 different types. PFGE could detect minor genetic variations among the isolates and could identify the variants which were not discriminated by RS-PCR. Four unique strain types detected by PFGE were not detected by RS-PCR. When applied to typing the outbreak-related strains from the vascular surgery unit at the General Infirmary at Leeds, the results of RS-PCR were identical to those of PFGE. Our results have shown that RS-PCR is a rapid, inexpensive technique that is highly reproducible and almost as discriminatory as PFGE for typing MRSA isolates and should be useful in the local investigation of MRSA outbreaks.

DNA, Bacterial↗
PubMed1994

Ribotyping of Staphylococcus aureus: an assessment using well-defined strains.

Ribotyping, with homologous or heterologous (Escherichia coli) r-RNA, of the propagating strains for phages of the international set for strains of Staphylococcus aureus of human origin was undertaken to determine the discrimination of this typing method. Ribotyping could distinguish between strains of different phage groups, but could not distinguish between seven phage group III strains of different phage type. Ribotying may be a useful adjunct to phage typing in S. aureus but is unlikely to replace it as the primary method of epidemiological typing.

Bacterial Typing Techniques↗
PubMed1993

Crystal structures of two cyclic pseudopentapeptides containing psi[CH2S] and psi[CH2SO] backbone surrogates.

The solid state conformations of cyclo [Gly-Pro psi[CH2S] Gly-D-Phe-Pro] and cyclo [Gly-Pro psi[CH2-(S)-SO]Gly-D-Phe-Pro] have been characterized by X-ray diffraction analysis. Crystals of the sulfide trihydrate are orthorhombic, P2(1)2(1)2(1), with a = 10.156(3) A, b = 11.704(3) A, c = 21.913(4) A, and Z = 4. Crystals of the sulfoxide are monoclinic, P2(1) with a = 10.662(1) A, b = 8.552(3) A, c = 12.947(2) A, beta = 94.28(2), and Z = 2. Unlike their all-amide parent, which adopts an all-trans backbone conformation and a type II beta-turn encompassing Gly-Pro-Gly-D-Phe, both of these peptides contain a cis Gly1-Pro2 bond and form a novel turn structure, i.e., a type II' beta-turn consisting of Gly-D-Phe-Pro-Gly. The turn structure in each of these peptides is stabilized by an intramolecular H bond between the carbonyl oxygen of Gly1 and the amide proton of D-Phe4. In the cyclic sulfoxide, the sulfinyl group is not involved in H bonding despite its strong potential as a hydrogen-bond acceptor. The crystal structure made it possible to establish the absolute configuration of the sulfinyl group in this peptide. The two crystal structures also helped identify a type II' beta-turn in the DMSO-d6 solution conformers of these peptides.

Amino Acid Sequence↗
PubMed1993

Characterization of a strain of methicillin-resistant Staphylococcus aureus (EMRSA-15) by conventional and molecular methods.

A strain of methicillin-resistant Staphylococcus aureus (MRSA), EMRSA-15, was isolated in both the Midlands and south-east of England. This strain could be distinguished from another, very similar strain, found in the north of England, by both conventional and molecular typing. Conventional typing allowed distinction between the Midlands and southern variants of EMRSA-15, while molecular typing (pulse-field gel electrophoresis) allowed recognition of local variants in the south. In this investigation conventional and molecular typing methods were complementary.

Bacterial Typing Techniques↗
PubMed1993

Distribution of mec regulator genes in methicillin-resistant Staphylococcus clinical strains.

The distributions of the mec regulator genes mecI and mecR1, which were identified on the chromosome of mecA-carrying Staphylococcus aureus N315, in methicillin-resistant staphylococci isolated in Japan and various countries were studied. Screening by dot blot hybridization by using polymerase chain reaction (PCR)-amplified probes revealed that at least the 5'-end region of the mecR1 gene was present in all strains tested, whereas about 40% of the strains were negative for the mecI gene. The data suggested that these regulator genes were the original components of the additional mec region DNA of methicillin-resistant S. aureus as well as methicillin-resistant, coagulase-negative staphylococci of seven staphylococcal species (S. epidermidis, S. haemolyticus, S. hominis, S. sciuri, S. capitis, S. caprae, and S. warneri). The mecI gene, which presumably codes for the repressor protein of the mecA gene, was found to harbor a point mutation in all six mecI-positive methicillin-resistant S. aureus strains, and their basal level of mecA gene transcription was elevated compared with that of strain N315, which harbors a presumably intact counterpart of the mecI gene. The data suggested that the mecI gene encodes for a strong repressor function on mecA gene transcription and is deleted or mutated in clinical methicillin-resistant S. aureus strains with high levels of resistance to methicillin.

Amino Acid Sequence↗