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Biomedical subjects

B Cookson

Publications and source records attributed to B Cookson.

At least 19 recordsLinked to original sources
PubMed1997

Reports on surveillance of antimicrobial resistance in individual countries.

In preparation for the meeting of the World Health Organization Working Group on Monitoring and Management of Bacterial Resistance to Antimicrobial Agents, representatives of 10 countries were asked to provide brief reports on the status of surveillance in their countries. Some gave extensive information on the methods used to test susceptibility of nosocomial pathogens to a variety of antibiotics; some described in detail the network of reference laboratories available to hospitals and individual clinicians for monitoring, identifying, and testing infectious agents; others chose to describe how their countries deal with the resistance of the most frequently isolated pathogen to a commonly used drug. The following summary of these reports shows the broad range of problems encountered and solutions undertaken by these 10 countries in dealing with the increasingly alarming problem of bacterial resistance to antimicrobial agents.

Algeria↗
PubMed1997

Rapid identification by specific PCR of coagulase-negative staphylococcal species important in hospital infection.

Polymerase chain reaction (PCR) identification assays were designed for eight major species of coagulase-negative staphylococci (CNS) on the basis of three variable regions found in the 16S rRNA gene. The PCR assays were tested with 41 staphylococcal strains representing the diversity of staphylococci defined by classical biotyping schemes. Each PCR result was compared with species-specific polymorphism in and around the 16S rRNA gene (i.e., 16S ribotype) and the phenotypic identification of the strain in a miniaturised biochemical test gallery (bioMerieux ATB 32 Staph). Twenty-six of the 41 strains were identified by PCR as belonging to one of the eight species for which primers had been designed and none of the remaining strains was misidentified. For 22 of the 26 strains there was complete agreement between the PCR identification, 16S ribotype and ATB identification. For the remaining four strains there was agreement between PCR identification and 16S ribotype. Two National Collection of Type Culture strains were re-assigned to different species and 10 previously unassigned strains were formally speciated for the first time. These PCR assays are suitable for rapid and definitive speciation of CNS.

Bacterial Typing Techniques↗
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↗
PubMed1995

Plasmid-mediated vanB glycopeptide resistance in enterococci.

Enterococcus faecium, which was highly resistant to vancomycin (MIC 256 mg/liter), but susceptible to teicoplanin (MIC 2 mg/liter), caused two distinct episodes of infection on a renal unit in the United Kingdom. Pulsed field gel electrophoresis (PFGE) indicated that a single strain caused the first episode, while the second episode, which occurred 1 year later, involved multiple strains, all of which were distinct from the original strain. Vancomycin resistance in all but one of these strains was mediated by transferable plasmids that carried the vanB glycopeptide resistance gene. Transfer either of resistance plasmids or the vanB resistance determinant itself to different strains occurred during the second episode. Plasmid-mediated vanB resistance has not been widely documented. A retrospective study of a reference collection revealed two other vanB-encoding plasmids from an E. faecalis and an E. faecium referred from two further UK centers. Although restriction analysis indicated no similarity between the plasmids from the three different centers, all contained a 2.1-kb EcoRV fragment that hybridized with a probe for the vanB gene. This suggests that there has been dissemination of a conserved glycopeptide resistance determinant, of which vanB is a part.

Anti-Bacterial Agents↗
PubMed1995

Bordetella hinzii sp. nov., isolated from poultry and humans.

A polyphasic taxonomic study that included DNA-rRNA hybridizations, DNA-DNA hybridizations, DNA base ratio determinations, whole-cell protein and fatty acid analyses, and an examination of classical phenotypic characteristics was performed in order to classify human and veterinary isolates that resemble Bordetella avium. Twelve poultry isolates and two human isolates were assigned to a new species, for which we propose the name Bordetella hinzii. The position of this organism in the family Alcaligenaceae and various genotypic, phenotypic, and chemotaxonomic characteristics are described.

Animals↗
PubMed1995

Aspects of the epidemiology of MRSA in Europe.

The prevalence of methicillin-resistant Staphylococcus aureus (MRSA) varies in different European countries, in different cities in the same country or even within a city or a hospital. It is thought that the overall incidence of MRSA is higher than ever before, although the reasons for this are unclear. MRSA typing can identify epidemic MRSA in many countries. The spread of a closely related clone is Northern Europe is a cause for concern, as it is resistant to many agents. In the UK, control measures are threatened by changing patterns of health care and patient demography. Resistance to mupirocin, a valuable agent in the control of MRSA, has emerged in many hospitals in the UK, thus the agent must be used judiciously.

Humans↗
PubMed1993

Comparison of high-level gentamicin-resistant Enterococcus faecium isolates from different continents.

Eight clinical isolates of Enterococcus faecium highly resistant to gentamicin (MIC, > 1,000 mg/liter) from patients in six hospitals on three continents were investigated for evidence of spread of either a clone of high-level gentamicin-resistant (HLGR) E. faecium or wide dissemination of a gentamicin resistance (Gmr) plasmid. A combination of ribotypes, plasmid profiles, and extended antimicrobial susceptibilities enabled us to distinguish all but two of the isolates and did not suggest clonal dissemination of a single strain. Two isolates from hospitals situated close together appeared identical by these methods. All of the isolates carried Gmr plasmids which appeared to be closely related following digestion with restriction endonucleases. Cross-hybridization studies confirmed extensive DNA homology between these plasmids. The fragments of these plasmids which hybridized with a probe specific for the aac6'aph2" resistance gene did not resemble those seen in the Gmr transposon Tn5281, which was characterized previously in E. faecalis HH22. This study suggests that there has been widespread dissemination of a single Gmr plasmid and its derivatives amongst isolates of HLGR E. faecium, although a Gmr plasmid from an HLGR E. faecium isolated in the United States showed little homology with the other Gmr plasmids studied.

Conjugation, Genetic↗
PubMed1993

Application of DNA probes for rRNA and vanA genes to investigation of a nosocomial cluster of vancomycin-resistant enterococci.

DNA probes specific for genes encoding rRNA and the glycopeptide resistance gene vanA were used to investigate a cluster of vancomycin-resistant (MICs, > 512 mg/liter) Enterococcus faecalis and Enterococcus faecium isolated from separate patients in a renal unit in a London hospital. When digested with BamHI, 12 of 13 vancomycin-resistant E. faecalis isolates exhibited a common restriction fragment length polymorphism pattern of rRNA genes (ribotype). A vanA probe hybridized with chromosomal DNA in these 12 isolates. The other isolate of vancomycin-resistant E. faecalis had a different ribotype and the vanA gene was located on plasmid DNA. These data suggest that cross-infection with a single strain of vancomycin-resistant E. faecalis occurred in most instances. In contrast, 23 vancomycin-resistant E. faecium isolates showed greater heterogeneity, comprising 8 ribotypes, suggesting that multiple strains were present in the unit. Twenty-one of these 23 isolates harbored a 24-MDa plasmid which hybridized with the vanA probe, implying that interstrain dissemination of a vancomycin resistance plasmid may have occurred among E. faecium isolates in the renal unit.

Bacterial Proteins↗
PubMed1992

Evaluation of methods for typing coagulase-negative staphylococci.

One hundred and forty-two coagulase-negative staphylococci (CNS) isolated from dialysate effluent or skin of patients receiving continuous ambulatory peritoneal dialysis (CAPD) were typed by extended antibiogram (16 antibiotics) and biotype (26 reactions). These isolates were then typed by supplementary methods to determine the most suitable typing method for an epidemiological study of antibiotic resistance. These included phage typing, reverse phage typing, plasmid typing, whole-cell protein typing by SDS-PAGE with analysis by densitometry, and immunoblotting. The percentage of isolates typed successfully by the supplementary methods were: phage typing 20%, reverse phage typing 0%, plasmid typing 66%, SDS-PAGE 100%, immunoblotting 100%. The discrimination of each method was: phage typing 20%, plasmid typing 37%, SDS-PAGE 69%, immunoblotting 57%. Reproducibility was 88% for phage typing and 97% for plasmid typing. The reproducibility of the whole-cell protein typing was 83% if the same extracts were used but only 43% when separate protein extracts were analysed on separate occasions. However, strain relatedness was highly reproducible. The determination of an antibiogram-biotype profile was not a sufficiently accurate typing method for an epidemiological study of antibiotic resistance. Whole-cell protein typing by SDS-PAGE or immunoblotting was technically demanding but was the most effective of the supplementary methods for detecting erroneous discrimination and false matching produced by antibiogram-biotype combinations.

Bacterial Proteins↗
PubMed1991

Typing of methicillin resistant and susceptible Staphylococcus aureus strains by ribosomal RNA gene restriction patterns using a biotinylated probe.

Nine methicillin-sensitive (MSSA) and 37 methicillin-resistant (MRSA) Staphylococcus aureus isolates of various phage types and resistotypes from seven countries were investigated. Chromosomal DNA was restricted with HindIII or EcoRI, Southern blotted and hybridised with a cDNA probe to 16S+23S rRNA derived from MRSA NCTC 10442. Resulting rDNA profiles could be differentiated on the basis of 22 patterns which were unaffected by changes in plasmid, transposon, enterotoxin A or phage content. Percentage similarity values were calculated using the Dice coefficient and UPGA clustering. Australian and epidemic (EMRSA-1) isolates from the UK showed a high degree of similarity, but the pattern was not unique and was also found in MSSA and other MRSA, e.g. NCTC 10442. An MSSA of phage group II was the most distinct isolate. The method shows potential as an additional tool in a complex typing system, types non-phage typable strains and may provide clues to the clonal evolution of MRSA and MSSA.

Bacterial Typing Techniques↗
PubMed1991

Effects of Bordetella pertussis infection on human respiratory epithelium in vivo and in vitro.

Bordetella pertussis infection probably involves attachment to and destruction of ciliated epithelial cells, but most previous studies have used animal tissue. During an epidemic, nasal epithelial biopsy specimens of 15 children (aged 1 month to 3 1/2 years) with whooping cough were examined for ciliary beat frequency, percent ciliation of the epithelium, and ciliary and epithelial cell ultrastructure. In addition, the in vitro effects of filtrates from a 24-h broth culture and of tracheal cytotoxin derived from B. pertussis on human nasal tissue organ culture were measured. B. pertussis was cultured from nasal swabs from 12 children. The mean ciliary beat frequency of their nasal biopsy specimens, 11.3 Hz (range, 10.4 to 13.0 Hz) was similar to that found in biopsy specimens from 10 normal children (mean, 12.5 Hz; range, 11.8 to 13.5 Hz). The abnormalities of the epithelium observed in 14 of 15 patients were a reduction in the number of ciliated cells, an increase in the number of cells with sparse ciliation, an increase in the number of dead cells, and extrusion of cells from the epithelial surface. In vitro, neither culture filtrate nor tracheal cytotoxin had any acute effect on ciliary function, but culture filtrate and tracheal cytotoxin (1 and 5 microM, respectively) caused extrusion of cells from the epithelial surface of turbinate tissue, loss of ciliated cells, an increased frequency of sparsely ciliated cells, and toxic changes in some cells. These changes were dose dependent and progressive, and between 36 and 90 h ciliary beating ceased. The observations made with patient tissue confirm that B. pertussis infection damages ciliated epithelium, and the in vitro experiments suggest that tracheal cytotoxin may be responsible for the abnormalities observed in vivo.

Bacterial Adhesion↗
PubMed1990

Diversity of staphylococci exhibiting high-level resistance to mupirocin.

Plasmids mediating high-level resistance to mupirocin (MIC greater than 1000 mg/L) in staphylococci from various sources were studied by restriction endonuclease cleavage. Several patterns were obtained but six plasmids isolated from various Staphylococcus aureus and S. epidermidis strains were indistinguishable. The diversity and spread of these plasmids is illustrated.

Coagulase↗