Publications (16)78.28 Total impact
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Article: Prolonged outbreak of meticillin-resistant Staphylococcus aureus in a cardiac surgery unit linked to a single colonized healthcare worker.
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ABSTRACT: BACKGROUND: In low- as well as in high-prevalence settings, healthcare workers (HCWs) may be a substantial, under-recognized, reservoir of meticillin-resistant Staphylococcus aureus (MRSA) and an important potential source of transmission to patients. AIM: To report an outbreak of MRSA in a cardiac surgery unit in England over a 10-month period. METHODS: Cases were defined as patients and staff on the cardiac surgery unit from whom the outbreak strain was newly isolated between 20 May 2011 and 16 March 2012. Representative isolates from all cases were characterized by spa-typing, pulsed-field gel electrophoresis and multi-locus variable-number tandem-repeat analysis (MLVA). FINDINGS: Four patients appeared to acquire MRSA during their inpatient stay on the cardiac surgery unit. All four patients and one HCW were found to be carrying an identical epidemic (E)MRSA-15 strain (spa t032, pulsotype A, MLVA profile 16-6-3-1-1-17-1-4). No other members of staff were found to be colonized with MRSA. The colonized HCW was thought to be the source of the outbreak and was decolonized using a combination of nasal mupirocin, chlorhexidine body wash and oral rifampicin and doxycycline. CONCLUSIONS: This report highlights recent changes in the epidemiology of MRSA in England and suggests an important role for colonized HCWs in the transmission of MRSA to patients. Screening HCWs may provide an increasingly valuable strategy in managing linked hospital acquisitions and well-defined outbreaks where initial investigation does not reveal a source.The Journal of hospital infection 01/2013; · 3.01 Impact Factor -
Article: Escherichia coli bacteraemia: how preventable is it?
The Journal of hospital infection 02/2012; 80(4):355-6. · 3.01 Impact Factor -
Article: Staff-to-patient transmission of meticillin-resistant Staphylococcus aureus: do bacterial factors play a role?
The Journal of hospital infection 08/2011; 79(3):275-7. · 3.01 Impact Factor -
Article: Impact of preoperative screening for meticillin-resistant Staphylococcus aureus by real-time polymerase chain reaction in patients undergoing cardiac surgery.
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ABSTRACT: We report a significant reduction in the number of surgical site infections (SSIs) due to meticillin-resistant Staphylococcus aureus (MRSA) in patients undergoing cardiac surgery after the introduction of preoperative screening using a same-day polymerase chain reaction (PCR) test. This was an observational cohort study set in a cardiac surgery unit based in southwest England. We studied 1462 patients admitted for cardiac surgery between October 2004 and September 2006. The IDI MRSA PCR test was used preoperatively to screen 765 patients between October 2005 and September 2006. Patients identified as carriers were treated with nasal mupirocin ointment and topical triclosan for five days, with single-dose teicoplanin instead of flucloxacillin as perioperative antibiotic prophylaxis. The rate of SSI following cardiac surgery in this group was compared to 697 patients who underwent surgery without screening between October 2004 and September 2005. After introduction of PCR screening, the overall rate of SSI fell from 3.30% to 2.22% with a significant reduction in the rate of MRSA infections (relative risk reduction: 0.77; 95% confidence interval: 0.056-0.95). PCR screening combined with suppression of MRSA at the time of cardiac surgery is feasible in routine clinical practice and is associated with a significant reduction in subsequent MRSA SSIs.Journal of Hospital Infection 07/2008; 69(2):124-30. · 3.39 Impact Factor -
Article: Identification of nonessential Helicobacter pylori genes using random mutagenesis and loop amplification.
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ABSTRACT: Analysis of the published genome sequences of Helicobacter pylori revealed that approximately 40% of the predicted open reading frames (ORFs) were of unknown function. We have developed the random mutagenesis and loop amplification (RMLA) strategy, and used this approach both to characterize individual virulence factors and to collectively screen comparatively large numbers of H. pylori mutants to identify genes that are not essential for viability in vitro. The mini-Tn3-Km transposon was used to generate a random mutant library in H. pylori strain G27. By screening the library of mutants we were able to demonstrate that the transposon integrated randomly into the chromosome of H. pylori and that RMLA was able to identify mutants in known virulence genes (urease and catalase). To test whether this strategy could be used as a high-throughput approach for the simultaneous identification of a series of nonessential genes of H. pylori, the transposon-chromosomal junctions of a pool of mutants were amplified by inverse PCR using circular fragments of genomic DNA obtained after chromosomal DNA extracted from the pool of mutants had been digested with HindIII and self-ligated. The amplification products were radioactively labelled and hybridized to a high density macroarray membrane containing a duplicated target sequence for every gene of H. pylori strain 26695. For the positive ORFs the precise site of transposon insertion was confirmed by PCR mapping. In total 78 H. pylori genes were unambiguously identified as nonessential for viability in vitro, including 20 with orthologues of unknown function in other species and 21 which were H. pylori-specific.Research in Microbiology 11/2001; 152(8):725-34. · 2.76 Impact Factor -
Article: Differentiation of metronidazole-sensitive and -resistant clinical isolates of Helicobacter pylori by immunoblotting with antisera to the RdxA protein.
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ABSTRACT: Antimicrobial resistance in Helicobacter pylori is a serious and increasing problem, and the development of rapid, reliable methods for detecting resistance would greatly improve the selection of antibiotics used to treat gastric infection with this organism. We assessed whether detection of the RdxA protein could provide the basis for determining the susceptibility of H. pylori to metronidazole. In order to raise polyclonal antisera to RdxA, we cloned the rdxA gene from H. pylori strain 26695 into the commercial expression vector pMAL-c2, purified the resultant fusion protein by affinity chromatography, and used this recombinant RdxA preparation to immunize rabbits. We then used this specific anti-RdxA antibody to perform immunoblotting on whole bacterial cell lysates of 17 metronidazole-sensitive and 27 metronidazole-resistant clinical isolates of H. pylori. While a 24-kDa immunoreactive band corresponding to the RdxA protein was observed in all metronidazole-sensitive strains, this band was absent in 25 of 27 resistant isolates. Our results indicate that testing for the absence of the RdxA protein would identify the majority of clinical isolates that will respond poorly to metronidazole-containing eradication regimens and have implications for the development of assays capable of detecting metronidazole resistance in H. pylori.Journal of Clinical Microbiology 10/2001; 39(9):3052-5. · 4.15 Impact Factor -
Article: Helicobacter pylori: towards new therapeutic targets.
Journal of Medical Microbiology 07/2001; 50(6):485-8. · 2.50 Impact Factor -
Article: Short-term infection with Helicobacter pylori and 1 week exposure to metronidazole does not enhance gastric mutation frequency in transgenic mice.
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ABSTRACT: The aim of this study was to determine whether exposure of Helicobacter pylori-infected mice to metronidazole resulted in the delivery of mutagenic compounds to the gastric epithelium via the oxygen-insensitive NADPH nitroreductase (RdxA) of H. pylori. C57BL/6 transgenic mice containing the lambda/lacI transgene were inoculated with peptone trypsin broth, H. pylori SS1 or SS1-rdxA(-), an SS1-derived mutant in rdxA. Twelve weeks after inoculation, the mice were treated for 7 days with a control solution or with the mouse equivalent of a human dose of metronidazole 1 g od. Three weeks after completion of treatment, the animals were killed and mutations in the target lacI gene assessed by a transgenic mutagenesis assay system. There was no increase in lacI mutations in cells harvested from mice infected with H. pylori and/or exposed to metronidazole. These data suggest that short-term infection with H. pylori and exposure to metronidazole does not enhance the mutation frequency in the gastric cells of mice. Whether chronic infection and/or repeated exposure to metronidazole or other nitroaromatic compounds causes genetic damage to gastric epithelial cells remains to be determined.Journal of Antimicrobial Chemotherapy 01/2001; 46(6):987-92. · 5.07 Impact Factor -
Article: Evaluation of nitrofurantoin combination therapy of metronidazole-sensitive and -resistant Helicobacter pylori infections in mice.
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ABSTRACT: The main objectives of this study were to determine whether the nitroreductase enzyme encoded by the rdxA gene of Helicobacter pylori was responsible for reductive activation of nitrofurantoin and whether a triple-therapy regimen with nitrofurantoin was able to eradicate metronidazole-sensitive and -resistant H. pylori infections from mice. The susceptibilities to nitrofurantoin of parent and isogenic rdxA mutant strains (three pairs), as well as a series of matched metronidazole-sensitive and -resistant strains isolated from mice (30) and patients (20), were assessed by agar dilution determination of the MIC. Groups of mice colonized with the metronidazole-sensitive H. pylori SS1 strain or a metronidazole-resistant rdxA SS1 mutant were treated with either metronidazole or nitrofurantoin as part of a triple-therapy regimen. One month after the completion of treatment the mice were sacrificed and their stomachs were cultured for H. pylori. The nitrofurantoin MICs for all strains tested were between 0.5 and 4.0 microg/ml. There was no significant difference between the susceptibility to nitrofurantoin of the parental strains and those of respective rdxA mutants or between those of matched metronidazole-sensitive and -resistant H. pylori isolates. The regimen with metronidazole eradicated infection from all eight SS1-infected mice and from one of eight mice inoculated with the rdxA mutant (P < or =0.001). The regimen with nitrofurantoin failed to eradicate infection from any of the six SS1-infected mice (P < or =0.001) and cleared infection from one of seven mice inoculated with the rdxA mutant. These results demonstrate that, despite the good in vitro activity of nitrofurantoin against H. pylori and the lack of cross-resistance between metronidazole and nitrofurantoin, eradication regimens involving nitrofurantoin are unable to eradicate either metronidazole-sensitive or -resistant H. pylori infections from mice.Antimicrobial Agents and Chemotherapy 10/2000; 44(10):2623-9. · 4.84 Impact Factor -
Article: Frequent association between alteration of the rdxA gene and metronidazole resistance in French and North African isolates of Helicobacter pylori.
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ABSTRACT: Mutations in the rdxA gene have been associated with the acquisition of resistance to metronidazole in Helicobacter pylori. This gene encodes an NADPH nitroreductase whose expression is necessary for intracellular activation of the drug. We wished to examine whether mutations in rdxA were present in resistant H. pylori isolates infecting either French or North African patients. We determined the complete nucleotide sequences of the rdxA genes from seven French and six North African patients infected with paired resistant and sensitive strains. Genotyping by random amplified polymorphic DNA analysis confirmed the close genetic relatedness of the susceptible and resistant isolates from individual biopsies. Eight French and five North African individual resistant strains were also studied. For the French strains, an alteration in rdxA most probably implicated in resistance was found in 10 cases (seven frameshift mutations, two missense mutations, and one deletion of 211 bp). One to three putative missense mutations were identified in four cases, and a missense mutation possibly not implicated in resistance was discovered in the last case. For the North African strains, an alteration in rdxA was found in eight cases (three frameshift mutations, three missense mutations, one deletion of 6 bp, and one insertion of a variant of IS605). Two strains contained putative missense mutations, and no change was observed in rdxA of the last strain. Thus, inactivation of the rdxA gene is frequently, but not always, associated with resistance to metronidazole in French and North African clinical isolates of H. pylori. In addition, a variety of alterations of rdxA are associated with the resistant phenotype.Antimicrobial Agents and Chemotherapy 04/2000; 44(3):608-13. · 4.84 Impact Factor -
Article: The role of the rdxA gene in the evolution of metronidazole resistance in Helicobacter pylori.
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ABSTRACT: It was recently demonstrated that inactivation of the rdxA gene, which encodes an oxygen-insensitive NADPH nitroreductase, is associated with the development of resistance to metronidazole by Helicobacter pylori. In order to further evaluate the contribution of rdxA to metronidazole resistance, the sequence of the rdxA gene was determined for a series of metronidazole-sensitive and -resistant isolates derived from a single, metronidazole-sensitive strain using an H. pylori mouse model. These strains were cultured from the stomachs of mice experimentally infected with H. pylori strain SS1 and then treated orally with metronidazole. The sequence of the rdxA gene of all 10 sequenced metronidazole-sensitive and two (7%) of the 27 metronidazole-resistant isolates was identical to that of the parental strain. In contrast, the rdxA gene of the other 25 metronidazole-resistant isolates contained between one and three frameshift or missense mutations. This suggests that while the development of metronidazole resistance in H. pylori is frequently associated with mutational inactivation of the rdxA gene, other mechanisms of resistance are likely to exist in this bacterium.Journal of Antimicrobial Chemotherapy 07/1999; 43(6):753-8. · 5.07 Impact Factor -
Article: Exposure to metronidazole in vivo readily induces resistance in Helicobacter pylori and reduces the efficacy of eradication therapy in mice.
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ABSTRACT: The Helicobacter pylori SS1 mouse model was used to characterize the development of resistance in H. pylori after treatment with metronidazole monotherapy and to examine the effect of prior exposure to metronidazole on the efficacy of a metronidazole-containing eradication regimen. Mice colonized with the metronidazole-sensitive H. pylori SS1 strain were treated for 7 days with either peptone trypsin broth or the mouse equivalent of 400 mg of metronidazole once a day or three times per day (TID). In a separate experiment, H. pylori-infected mice were administered either peptone trypsin broth or the mouse equivalent of 400 mg of metronidazole TID for 7 days, followed 1 month later by either peptone trypsin broth or the mouse equivalent of 20 mg of omeprazole, 250 mg of clarithromycin, and 400 mg of metronidazole twice a day for 7 days. At least 1 month after the completion of treatment, the mice were sacrificed and their stomachs were cultured for H. pylori. The susceptibilities of isolates to metronidazole were assessed by agar dilution determination of the MICs. Mixed populations of metronidazole-resistant and -sensitive strains were isolated from 70% of mice treated with 400 mg of metronidazole TID. The ratio of resistant to sensitive strains was 1:100, and the MICs for the resistant strains varied from 8 to 64 micrograms/ml. In the second experiment, H. pylori was eradicated from 70% of mice treated with eradication therapy alone, compared to 25% of mice pretreated with metronidazole (P < 0.01). Mice still infected after treatment with metronidazole and eradication therapy contained mixed populations of metronidazole-resistant and -sensitive isolates in a ratio of 1:25. These results demonstrate that H. pylori readily acquires resistance to metronidazole in vivo and that prior exposure of the organism to metronidazole is associated with failure of eradication therapy. H. pylori-infected mice provide a suitable model for the study of resistance mechanisms in H. pylori and will be useful in determining optimal regimens for the eradication of resistant strains.Antimicrobial Agents and Chemotherapy 05/1999; 43(4):777-81. · 4.84 Impact Factor -
Article: Microbial genome sequencing-beyond the double helix.
BMJ 01/1999; 317(7172):1568-71. · 14.09 Impact Factor -
Article: Clinical outcome after infection with Helicobacter pylori does not appear to be reliably predicted by the presence of any of the genes of the cag pathogenicity island.
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ABSTRACT: The development of clinical disease after infection with Helicobacter pylori has been reported to be associated with expression of the cagA gene. Recently, it has been shown that cagA is part of a multigene locus, described as the cag pathogenicity island (PAI). The role of this region in determining clinical outcome remains to be established. To investigate whether the presence of cagA is always associated with the presence of the complete cag PAI and to evaluate the distribution of selected cag genes in 73 H pylori strains isolated from patients in France. Clinical strains of H pylori were screened for selected genes of the cag PAI by polymerase chain reaction and colony hybridisation. Of 64 strains that harboured the cagA gene, 57 (89%) also contained the entire cag PAI. The entire cag PAI was found in 85% (48/56) and 53% (9/17) of duodenal ulcer and non-ulcer dyspepsia isolates, respectively. Eight strains had deletions within the cag PAI, including deletion of the cagA gene in one isolate; the deletions were not associated with the insertion sequence IS605. Of eight strains lacking the cag PAI, four were isolated from patients with duodenal ulcer. The cag PAI is not a uniform, conserved entity. Although the presence of the cag PAI is highly associated with duodenal ulcer, the clinical outcome of infection with H pylori is not reliably predicted by any gene of the cag PAI.Gut 01/1999; 43(6):752-8. · 10.11 Impact Factor -
Article: Susceptibility testing of Klebsiella spp.--an international collaborative study in quality assessment.
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ABSTRACT: In order to compare the prevalence of antibiotic resistance in different geographical areas, it is necessary to ensure agreement between laboratories on the assignment of strains to 'susceptible' and 'resistant' categories. An international quality assessment was performed to investigate the performance of susceptibility testing of Klebsiella spp. Ninety-five strains of klebsiellae were selected from clinical isolates at the London Hospital Medical College (LHMC). These included strains with a diversity of susceptibility profiles to amoxycillin/clavulanate, piperacillin, ceftazidime, cefuroxime, ciprofloxacin, gentamicin and trimethoprim. The strains were sent to 13 participating laboratories in Europe and the USA and laboratories were asked to test the susceptibility of these strains to these antibiotics by their usual methods. They were also asked to provide details of the method used to test susceptibility. Several different standard recommended testing methods were used. Reporting of susceptibilities was generally accurate, but a number of anomalies were noted. Discrepancies of reporting between the LHMC and the participating laboratories was more marked for resistant strains, particularly in the detection of resistance to cefuroxime and ciprofloxacin, as well as the assignment of susceptibility and resistance to piperacillin and amoxycillin/clavulanate. Some discrepancies could be attributed to the use of different breakpoints, leading to differing assignment of susceptibility. Methodological variations including disc content, inoculum and failure to measure and interpret zone sizes consistently also led to anomalies. This quality assessment programme has helped to identify problems in susceptibility testing which should be investigated further.Journal of Antimicrobial Chemotherapy 08/1998; 42(1):29-48. · 5.07 Impact Factor -
Article: Sequencing microbial genomes--what will it do for microbiology?
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ABSTRACT: In 1995, Haemophilus influenzae became the first free-living organism to have its entire genome sequence published. Since then, many similar projects have been started and, by the millennium, the genomes of a significant number of important human pathogens will have been sequenced. During this period of increasing access to microbial sequence data, parallel advances have occurred in techniques that allow the large-scale study of the entire genetic complement of micro-organisms. In the near future, these approaches will enable researchers to unravel further the complexity of microbial pathogenesis and identify new virulence determinants. Many of these will be suitable targets for development as diagnostic reagents, antimicrobial agents and vaccine candidates. Although it is difficult to predict the full impact that this almost overwhelming volume of information will have on the practice of microbiology, it is clear that it will result ultimately in new ways of diagnosing and combating infectious diseases.Journal of Medical Microbiology 06/1998; 47(5):375-82. · 2.50 Impact Factor
Top co-authors
Top Journals
Institutions
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2008–2013
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Derriford Hospital
Plymouth, ENG, United Kingdom
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2001
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Nottingham University Hospitals NHS
Nottingham, ENG, United Kingdom
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1998–2001
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Institut Pasteur Paris
Paris, Ile-de-France, France
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