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Hilary Humphreys

Publications and source records attributed to Hilary Humphreys.

11 recordsLinked to original sources
PubMed2005

Evidence for icaADBC-independent biofilm development mechanism in methicillin-resistant Staphylococcus aureus clinical isolates.

Synthesis of a polysaccharide adhesin by icaADBC-encoded enzymes is currently the best-understood mechanism of staphylococcal biofilm development. In four methicillin-resistant Staphylococcus aureus isolates, environmental activation of icaADBC did not always correlate with increased biofilm production. Moreover, glucose-mediated biofilm development in these isolates was icaADBC independent. Apparently, an environmentally regulated, ica-independent mechanism(s) of biofilm development exists in S. aureus clinical isolates.

Bacterial Proteins↗
PubMed2004

Inactivations of rsbU and sarA by IS256 represent novel mechanisms of biofilm phenotypic variation in Staphylococcus epidermidis.

Expression of ica operon-mediated biofilm formation in Staphylococcus epidermidis RP62A is subject to phase variable regulation. Reversible transposition of IS256 into icaADBC or downregulation of icaADBC expression are two important mechanisms of biofilm phenotypic variation. Interestingly, the presence of IS256 was generally associated with a more rapid rate of phenotypic variation, suggesting that IS256 insertions outside the ica locus may affect ica transcription. Consistent with this, we identified variants with diminished ica expression, which were associated with IS256 insertions in the sigmaB activator rsbU or sarA. Biofilm development and ica expression were activated only by ethanol and not NaCl in rsbU::IS256 insertion variants, which were present in approximately 11% of all variants. sigmaB activity was impaired in rsbU::IS256 variants, as evidenced by reduced expression of the sigmaB-regulated genes asp23, csb9, and rsbV. Moreover, expression of sarA, which is sigmaB regulated, and SarA-regulated RNAIII were also suppressed. A biofilm-forming phenotype was restored to rsbU::IS256 variants only after repeated passage and was not associated with IS256 excision from rsbU. Only one sarA::IS256 insertion mutant was identified among 43 biofilm-negative variants. Both NaCl and ethanol-activated ica expression in this sarA::IS256 variant, but only ethanol increased biofilm development. Unlike rsbU::IS256 variants, reversion of the sarA::IS256 variant to a biofilm-positive phenotype was accompanied by precise excision of IS256 from sarA and restoration of normal ica expression. These data identify new roles for IS256 in ica and biofilm phenotypic variation and demonstrate the capacity of this element to influence the global regulation of transcription in S. epidermidis.

Bacterial Proteins↗
PubMed2002

Regulation of icaR gene expression in Staphylococcus epidermidis.

LightCycler and conventional reverse transcription-polymerase chain reaction (RT-PCR) were used to examine regulation of icaR, which encodes a repressor of the Staphylococcus epidermidis ica operon. Varying concentrations of NaCl and ethanol activated ica but only high levels of both compounds repressed icaR transcription. Activation of ica by subinhibitory concentrations of tetracycline, which was strain-dependent, was also associated with icaR repression. In an ICAR::Em mutant, NaCl but not ethanol activated ica whereas both compounds repressed icaR expression indicating that environmental regulation of the icaR gene is IcaR-independent. Apparently ethanol signals exclusively through IcaR to activate ica and regulates IcaR at the transcriptional and posttranscriptional levels. NaCl also regulates icaR expression but in addition can activate ica via an icaR-independent pathway.

Bacterial Proteins↗
PubMed2002

Sixteen years' surveillance of surgical sites in an Irish acute-care hospital.

OBJECTIVE: To report a program of continuous surveillance of surgical-site infections (SSIs) using basic surveillance methods. DESIGN: Analysis of routine prospective surveillance data. SETTING: Two hospitals in Ireland (300 and 350 beds) that merged and moved to a new 650-bed hospital in 1987. PATIENTS: 59,335 surgical sites of postoperative patients. INTERVENTIONS: Surgical sites were surveyed by one infection control nurse and SSI rates were produced for selected operations and surgical services. The program was conducted in general accordance with the 1999 HICPAC guidelines, but differed in surveillance strategy. Operations were limited to two to three risk classifications, assigned by the infection control nurse. RESULTS: The overall SSI rate was 4.5%, with 2.4% in clean surgery. Apart from increases in the 3rd, 4th, 13th, and 14th years, rates remained relatively stable during the 16 years. Few significant decreases in SSI rates in surgical services or specific operations were shown, apart from the following: vascular surgery, 8.1% to 5% between the first 8 years and the last 8 years; general surgery services, 9% to 5%, and gynecology, 15.8% to 1.7%, both in the first year compared with in subsequent years; and gastric operations, 21% to 4.3% between the first year and the second year. Organ/space infection was identified in 0.5% of 17,804 operations, including 0.4% meningitis after neurosurgical procedures, 3% graft infections after vascular bypass operations, and 0.2% intra-abdominal infections after abdominal surgery. CONCLUSIONS: With the use of basic principles of surveillance and modest resources, procedure-specific SSI rates were produced, with little significant change during the 16 years. Despite limitations in case-finding, risk stratification, feedback, and surveillance methods, the overall SSI rates were comparable with other published data.

Cross Infection↗
PubMed2002

icaR encodes a transcriptional repressor involved in environmental regulation of ica operon expression and biofilm formation in Staphylococcus epidermidis.

Biofilm formation in Staphylococcus epidermidis is dependent upon the ica operon-encoded polysaccharide intercellular adhesin, which is subject to phase-variable and environmental regulation. The icaR gene, located adjacent to the ica operon, appears to be a member of the tetR family of transcriptional regulators. In the reference strain RP62A, reversible inactivation of the ica operon by IS256 accounts for 25 to 33% of phase variants. In this study, icaA and icaR regulation were compared in RP62A and a biofilm-forming clinical isolate, CSF41498, in which IS256 is absent. Predictably, ica operon expression was detected only in wild-type CSF41498 and RP62A but not in non-IS256-generated phase variants. In contrast, the icaR gene was not expressed in RP62A phase variants but was expressed in CSF41498 variants. An icaR::Em(r) insertion mutation in CSF41498 resulted in an at least a 5.8-fold increase in ica operon expression but did not significantly alter regulation of the icaR gene itself. Activation of ica operon transcription by ethanol in CSF41498 was icaR dependent. In contrast, a small but significant induction of ica by NaCl and glucose (NaCl-glucose) was observed in the icaR::Em(r) mutant. In addition, transcription of the icaR gene itself was not significantly affected by NaCl-glucose but was repressed by ethanol. Expression of the ica operon was induced by ethanol or NaCl-glucose in phase variants of CSF41498 (icaR+) but not in RP62A variants (icaR deficient). These data indicate that icaR encodes a repressor of ica operon transcription required for ethanol but not NaCl-glucose activation of ica operon expression and biofilm formation.

Biofilms↗
PubMed2001

Staphylococcus epidermidis biofilms: importance and implications.

The coagulase-negative staphylococci and, in particular, Staphylococcus epidermidis, have emerged as major nosocomial pathogens associated with infections of implanted medical devices. These organisms, which are among the most prevalent bacteria of the human skin and mucous membrane microflora, present unique problems in the diagnosis and treatment of infections involving biofilm formation on implanted biomaterials. Epidemiological data that address whether invasive S. epidermidis strains can be traced to commensal organisms or an endemic occurrence of distinct strains with enhanced virulence have important implications for the implementation of appropriate infection control measures. An extracellular polysaccharide adhesin represents a key virulence determinant in S. epidermidis and is required for biofilm formation. Production of this adhesin, which is encoded by the ica operon, is subject to phase variable regulation (ON <---> OFF switching). Recent advances in understanding the molecular events controlling polysaccharide adhesin synthesis and the potential clinical implications of its phase variable regulation are outlined. Further research in this area may contribute to the development of novel strategies for therapeutic intervention. Finally, in addition to antibiotic prophylaxis, preventive strategies to control S. epidermidis medical device-related infections are focusing on the development of improved biomaterials and physical electrical barriers to impede bacterial colonisation.

Adhesins, Bacterial↗