Roger Bayston

Stimulation of Staphylococcus epidermidis growth and biofilm formation by catecholamine inotropes

BACKGROUND Bacterial colonisation of indwelling medical devices by coagulase-negative staphylococci is a prevalent risk in intensive-care units. Factors determining biofilm formation and progression to catheter- related infection are incompletely understood. We postulated that administration of inotropic agents via indwelling intravenous catheters may stimulate growth and formation of biofilms by Staphylococcus epidermidis. METHODS Inocula representing physiologically relevant infecting doses of S epidermidis were incubated in a minimum medium supplemented with fresh human plasma in the presence or absence of pharmacological concentrations of norepinephrine or dobutamine. Biofilm formation on polystyrene and medical-grade silicone was examined. After incubation, cultures were assessed for growth and formation of biofilms by colony counting and scanning electronmicroscopy. The production of exopolysaccharide, a major constituent of S epidermidis biofilms, was also assessed by use of immunofluorescence microscopy. FINDINGS Incubation of S epidermidis with catecholamine inotropes in the presence of human plasma resulted in a significant increase in growth compared with control on both polystyrene and silicone surfaces, with pronounced increases in biofilm formation as visualised by scanning electronmicroscopy. Experiments with transferrin labelled with radioactive iron showed the ability of catecholamine inotropes to facilitate acquisition of iron by S epidermidis. Immunofluorescence microscopy revealed extensive exopolysaccharide production associated with S epidermidis biofilms. INTERPRETATION The ability of catecholamine inotropic drugs to stimulate bacterial proliferation and biofilm formation may be an aetiological factor in the development of intravascular catheter colonisation and catheter-related infection. The removal of iron from transferrin for subsequent use by S epidermidis is a possible mechanism by which catecholamine inotropes stimulate bacterial growth as biofilms.

Spine update: prevention of postoperative infection in patients undergoing spinal surgery.

In a climate of clinical governance and evidence-based medicine, medical audit and other procedures are being used increasingly to evaluate clinical experience and as a basis for guidelines and recommendations on best clinical practice. In some areas of surgery and medicine, however, a structured approach is not possible because the data on which the assessments depend simply do not exist or are not sufficiently robust. This is the situation that applies to the use of systemic antibiotics for the prevention of infection following both spinal surgery and diagnostic and therapeutic procedures involving violation of one or more disc spaces, to the irrigation of spinal wounds with antibiotic or antiseptic solutions and to the use of drains in spinal surgery. In such circumstances, any attempt to provide guidance on the rational use of antibiotics must be based on a critical review of the relevant literature, experience in the management of neurosurgical/orthopedic infections, and a thorough knowledge of the antimicrobials currently available. Antibiotics are used widely, perhaps even routinely, to prevent postoperative infection in patients undergoing spinal surgery, but the evidence to support the efficacy of this intervention is not robust. For the purposes of this review, the role of antibiotic prophylaxis in spinal surgery will be considered under two headings: the prevention of surgical site (wound) infection in general following spinal surgery and the prevention of discitis specifically following procedures involving one or more discs. The roles of intraoperative antibiotic or antiseptic wound irrigation and drains in patients undergoing spinal surgery are also reviewed. Prophylaxis for patients undergoing spinal implant procedures will be addressed in a subsequent Working Party report dedicated to implant-associated infections.

Bacterial surface properties of clinically isolated Staphylococcus epidermidis strains determine adhesion on polyethylene

The role of surface physiochemical properties of Staphylococcus epidermidis strains in adhesion to polyethylene (PE) was investigated under physiological flow conditions in phosphate buffered saline (PBS) and 1% platelet poor plasma (PPP). Four clinically isolated strains were divided into two groups: low and high relative hydrophobicity, and the F1198 and RP62A strains showing significantly greater hydrophobicity than the F21 and F1018 strains. In PBS, adhesion of all S. epidermidis strains was shear dependent from 0 to 15 dyn/cm2, after which adhesion becomes shear independent. Strains with higher surface hydrophobicity showed higher adhesion to PE, demonstrating the influence of bacterial surface hydrophobicity in nonspecific adhesion. Bacterial adhesion correlated well with bacterial surface hydrophobicity at low shear stresses (0-8 dyn/cm2). In 1% PPP, adhesion of all strains dramatically decreased and we found no correlation between bacterial surface hydrophobicity and adhesion. The presence of plasma proteins reduced nonspecific adhesion. S. epidermidis surface charge did not correlate with bacterial adhesion in either test media. The results suggested that S. epidermidis surface hydrophobicity may mediate nonspecific adhesion to PE at low shear stresses in protein-free media.

Use of antibiotics in penetrating craniocerebral injuries

Summary The Working Party was instituted to investigate the rationale of prophylactic and therapeutic antibiotic use in penetrating craniocerebral injuries (PCCI), and to make recommendations for current practice. A systematic review of papers on civilian and military PCCI over the past 25 and 50 years, respectively, was done via electronic databases and secondary sources, and data were evaluated. Guidelines on the removal of indriven bone or metal fragments only if further neural damage can be avoided were supported. However, no publications were identified where the data on infection or its treatment and prevention were complete or satisfactorily derived, and no controlled trials have been published. All studies were retrospective or anecdotal. Working Party recommendations are based on the data available and the professional experience and knowledge of the members. Broad-spectrum antibiotic prophylaxis is recommended for both military and civilian PCCI, including those due to sports or recreational injuries.

The management of neurosurgical patients with postoperative bacterial or aseptic meningitis or external ventricular drain-associated

This article is dedicated to the management of neurosurgical patients who develop postoperative meningitis or external ventricular drain (EVD)-related ventriculitis. Postoperative meningitis is either bacterial or aseptic, the latter occurring more commonly. However, owing to difficulties associated with distinguishing between the two processes, all patients with the clinical and laboratory features of postoperative meningitis should receive empirical antibiotic therapy; if a cultured sample of CSF is sterile after incubation for 3 days, the antibiotics can be discontinued. Patients with confirmed bacterial meningitis should be treated with one of the organism-specific regimens provided. Also provided are recommendations for the management of patients with EVD-related ventriculitis and a strategy for preventing shunt infections in patients with EVDs who undergo implantation of CSF shunts.This article is dedicated to the management of neurosurgical patients who develop postoperative meningitis or external ventricular drain (EVD)-related ventriculitis. Postoperative meningitis is either bacterial or aseptic, the latter occurring more commonly. However, owing to difficulties associated with distinguishing between the two processes, all patients with the clinical and laboratory features of postoperative meningitis should receive empirical antibiotic therapy; if a cultured sample of CSF is sterile after incubation for 3 days, the antibiotics can be discontinued. Patients with confirmed bacterial meningitis should be treated with one of the organism-specific regimens provided. Also provided are recommendations for the management of patients with EVD-related ventriculitis and a strategy for preventing shunt infections in patients with EVDs who undergo implantation of CSF shunts.

The rational use of antibiotics in the treatment of brain abscess

The Working Party was instituted to investigate the rationale of therapeutic antibiotic usage in patients with brain abscess and to make recommendations for current practice. A systematic review of English language publications on brain abscess over the last 25 years was carried out using electronic databases and secondary sources, and data were evaluated. Few publications were identified where the microbiological procedures were adequately described and many authors continue to report sterile pus in a proportion of cases. The vast majority of reports were retrospective neurosurgical assessments in which details of laboratory procedures and antibiotic regimens were missing. There are no published reports of controlled clinical trials or comparative therapeutic studies. The recommendations made by the Working Party are based on relevant published information and the expertise of Working Party members. Recommendations vary according to the location of the abscess which reflects the likely source of the infection and therefore the bacterial types most likely to be present in aspirated pus. Bacteria with multiple resistance to antimicrobial agents do not feature significantly in cases of brain abscess.The Working Party was instituted to investigate the rationale of therapeutic antibiotic usage in patients with brain abscess and to make recommendations for current practice. A systematic review of English language publications on brain abscess over the last 25 years was carried out using electronic databases and secondary sources, and data were evaluated. Few publications were identified where the microbiological procedures were adequately described and many authors continue to report sterile pus in a proportion of cases.The vast majority of reports were retrospective neurosurgical assessments in which details of laboratory procedures and antibiotic regimens were missing.There are no published reports of controlled clinical trials or comparative therapeutic studies.The recommendations made by the Working Party are based on relevant published information and the expertise of Working Party members. Recommendations vary according to the location of the abscess which reflects the likely source of the infection and therefore the bacterial types most likely to be present in aspirated pus. Bacteria with multiple resistance to antimicrobial agents do not feature significantly in cases of brain abscess.

An antimicrobial modified silicone peritoneal catheter with activity against both Gram positive and Gram negative bacteria

Peritonitis, exit site and tunnel infections are serious complications of peritoneal dialysis (CAPD), which may lead to catheter loss, despite measures taken to reduce the infection rate. Catheters coated with antimicrobials have shown only short-term activity. We have developed a process for conferring broad-spectrum, long-duration antimicrobial activity on CAPD catheters while reducing the risk of resistance. Catheters were processed using an impregnation method. Three agents were used: rifampicin, triclosan and trimethoprim. Tests included establishing the duration of activity before test bacteria became resistant, the ability to kill 100% of attached bacteria in a predetermined time (tK100), and ability to withstand multiple high-count challenges until failure in a flow model. Antimicrobial activity continued until it was stopped at 280 days and the agents prevented the emergence of resistant strains. tK100 results showed a >99.9% reduction of attached bacteria. The flow model showed no colonization when repeatedly challenged with high loads of meticillin-resistant Staphylococcus aureus or Escherichia coli for approximately 90 days. The antimicrobial catheter material showed prolonged activity against common CAPD pathogens and promises to reduce clinical CAPD infection.

Biomaterial modification of urinary catheters with antimicrobials to give long-term broadspectrum antibiofilm activity

Catheter-associated urinary tract infection (CAUTI) is the commonest hospital-acquired infection, accounting for over 100,000 hospital admissions within the USA annually. Biomaterials and processes intended to reduce the risk of bacterial colonization of the catheters for long-term users have not been successful, mainly because of the need for long duration of activity in flow conditions. Here we report the results of impregnation of urinary catheters with a combination of rifampicin, sparfloxacin and triclosan. In flow experiments, the antimicrobial catheters were able to prevent colonization by common uropathogens Proteus mirabilis, Staphylococcus aureus and Escherichia coli for 7 to 12weeks in vitro compared with 1-3days for other, commercially available antimicrobial catheters currently used clinically. Resistance development was minimized by careful choice of antimicrobial combinations. Drug release profiles and distribution in the polymer, and surface analysis were also carried out and the process had no deleterious effect on the mechanical performance of the catheter or its balloon. The antimicrobial catheter therefore offers for the first time a means of reducing infection and its complications in long-term urinary catheter users.

Physical properties of cerebrospinal fluid of relevance to shunt function. 1: The effect of protein upon CSF viscosity.

Viscosity is the resistance to flow of a fluid and it is the only property of a fluid that will affect its flow through a system of valveless tubing (surface tension will affect the opening and closing of valves that are included in the system). The effect that an elevated protein concentration has upon CSF viscosity has received little study, yet many neurosurgeons believe that CSF with an elevated protein content is too viscous to flow satisfactorily through shunts. The total protein content and viscosity of 126 specimens of CSF from hydrocephalic patients were measured and analysed with reference to the aetiology of the hydrocephalus. The results indicate that high protein concentrations do not greatly affect the viscosity of CSF, and that the aetiology is also of little consequence. These findings were highly significant on linear regression analysis (p < 0.001). The flow of the most viscous CSF that is likely to be encountered would be reduced by only 7% through a given catheter, compared with that of the least viscous CSF.

In vitro antimicrobial activity of silver-processed catheters for neurosurgery

OBJECTIVES To investigate the in vitro antibacterial activity of silver-processed catheters for use in neurosurgery using clinically predictive tests. METHODS The antimicrobial activity of a commercially available silver-processed external ventricular drain catheter was evaluated against Staphylococcus epidermidis, methicillin-resistant Staphylococcus aureus (MRSA), Escherichia coli and Propionibacterium acnes. Non-impregnated catheters were used as controls. Two assays were performed: (i) testing the ability of the catheter to kill 100% of the attached bacteria (tK100); and (ii) in vitro challenge to determine the ability to prevent colonization under flow conditions. High and low inocula (10(4) and 10(7) cfu/mL) were used. Silver-processed and control catheters were examined by scanning electron microscopy and focused ion beam scanning electron microscopy; electron back-scatter and energy-dispersive X-ray analyses were used to investigate the distribution of silver within the processed catheter. RESULTS The silver-processed catheters were not able to kill any of the bacteria tested in the tK100 assay at high inoculum. At low inoculum S. epidermidis was eradicated and some activity was seen against E. coli but without complete eradication. MRSA was also not eradicated even at low inoculum. The in vitro challenge test showed no prevention of colonization for any of the strains. Silver particles were shown to be >500 nm in size. CONCLUSIONS The commercial silver-impregnated catheter was not able to eradicate MRSA or E. coli and while it showed activity against S. epidermidis in one assay it was unable to prevent colonization in vitro under in-flow conditions. This is consistent with clinical studies on silver-processed catheters.