An external ventricular drainage catheter impregnated with rifampicin, trimethoprim and triclosan, with extended activity against MDR Gram-negative bacteria: an in vitro and in vivo study.

BACKGROUND: External ventricular drainage (EVD) carries a high risk of ventriculitis, increasingly caused by MDR Gram-negative bacteria such as Escherichia coli and Acinetobacter baumannii. Existing antimicrobial EVD catheters are not effective against these, and we have developed a catheter with activity against MDR bacteria and demonstrated the safety of the new formulation for use in the brain. OBJECTIVES: Our aim was to determine the ability of a newly formulated impregnated EVD catheters to withstand challenge with MDR Gram-negative bacteria and to obtain information about its safety for use in the CNS. METHODS: Catheters impregnated with three antimicrobials (rifampicin, trimethoprim and triclosan) were challenged in flow conditions at four weekly timepoints with high doses of MDR bacteria, including MRSA and Acinetobacter, and monitored for bacterial colonization. Catheter segments were also inserted intracerebrally into Wistar rats, which were monitored for clinical and behavioural change, and weight loss. Brains were removed after either 1 week or 4 weeks, and examined for evidence of inflammation and toxicity. RESULTS: Control catheters colonized quickly after the first challenge, while no colonization occurred in the impregnated catheters even after the 4 week challenge. Animals receiving the antimicrobial segments behaved normally and gained weight as expected. Neurohistochemistry revealed only surgical trauma and no evidence of neurotoxicity. CONCLUSIONS: The antimicrobial catheter appears to withstand bacterial challenge for at least 4 weeks, suggesting that it might offer protection against infection with MDR Gram-negative bacteria in patients undergoing EVD. It also appears to be safe for use in the CNS.

Comparison of different human tissue processing methods for maximization of bacterial recovery.

Tissues are valuable microbiological samples that have proved superiority over swabs. Culture of tissue samples is used in the diagnosis of a variety of infections. However, as well as factors such as the site of obtaining the sample, the number of samples, and previous antibiotic use, the method of tissue processing may have an important effect on sensitivity. Data from the literature comparing different tissue processing methods is very limited. This study aimed to compare different mechanical and chemical methods of tissue processing in terms of efficacy and retaining the viability of the bacteria in the tissues. Standard suspensions of Staphylococcus aureus and Escherichia coli were prepared and treated differently to test the effect of that treatment on bacterial viability. Artificially inoculated pork tissue and known infected human tissue samples were then processed by different methods prior to culture, and results were compared. Percentages of reduction in the number of viable bacteria compared to the control by homogenization was similar to 5-min dithiothreitol treatment but significantly lower than bead beating. Bacterial recovery from homogenized human tissues was significantly higher than from any other method of treatment. Although bead beating could be the most efficient method in obtaining a homogeneous tissue product, it significantly reduces the number of viable bacteria within tissues. Homogenization offers the most effective easily controllable retrieval of bacteria from tissue and retains their viability. Guidelines for diagnosing infections using tissue samples should include a standardized processing method.

A tolerability and patient acceptability pilot study of a novel antimicrobial urinary catheter for long-term use.

AIMS: We have developed a novel antimicrobial urinary catheter (AUC) impregnated with rifampicin, triclosan, and sparfloxacin and demonstrated that it has long-term (∼84 days) protection against bacterial colonization in vitro. This study aimed to assess the safety and patient acceptability of this device in long-term catheter users. METHODS: Adults who use long term (>28 days) indwelling urinary catheters with capacity to consent were invited to receive the AUC at their next catheter change. The primary outcome measure was adverse events (AE) attributable to antimicrobial impregnation of the catheter. Secondary outcome measures included severity of related AEs, patient acceptability, early removal of the trial catheter, and degree of microbial colonization of trial catheters. Except for the last, outcomes were assessed by telephone interviews. Original and trial catheters were collected, and the lumens and balloons were separated and analyzed for microbiological colonization. RESULTS: Thirty participants were recruited. Eighty four AEs were reported, and only one was rated as "probably" related to antimicrobial impregnation. The AE was mild and resolved within 48 h. A total of 82.14% of participants rated the catheter as no different or better than their usual catheter. Two participants chose to remove the AUC early due to it feeling shorter. There were significantly fewer bacterial isolates attached to the balloons of trial catheters compared to the matched original catheters. CONCLUSIONS: The AUC has an advantageous safety profile and was acceptable to the majority of participants. Information gained from this trial will support a larger randomized controlled study of efficacy.

Propidium monoazide-polymerase chain reaction for detection of residual periprosthetic joint infection in two-stage revision.

False negative culture results in periprosthetic joint infection (PJI) are not uncommon particularly when patients have received long term antibiotics. Polymerase chain reaction (PCR) has a lower specificity partly due to detection of residual DNA from dead bacteria. Propidium monoazide (PMA) prevents DNA from dead bacteria from being amplified during the PCR. This study aimed to determine the role of PMA in PCR for diagnosis of PJI. Clinical samples were tested by PCR with and without prior treatment with PMA and compared to conventional microbiological culture. The PCR assay included genus-specific primers for staphylococci and enterococci and species-specific primers for Cutibacterium acnes. The validated conditions of PMA treatment used in this study were 20 µM concentration and 5 and 10 min of dark incubation and photo-activation respectively. 202 periprosthetic tissues and explanted prostheses from 60 episodes in 58 patients undergoing revision arthroplasties for either PJI or non-infective causes were tested, by culture, PCR, and PMA-PCR. 14 of the 60 episodes satisfied the Musculoskeletal Infection Society (MSIS) criteria for PJI and 46 did not. Sensitivity of culture, PCR, and PMA-PCR were 50%, 71%, and 79% respectively. Specificities were 98%, 72%, and 89% respectively. All figures were calculated for episodes rather than samples. PMA-PCR enhanced both the specificity and the sensitivity of PCR. It has the potential to detect residual bacterial viability prior to reimplantation in the two-stage revision for PJI.

Prospective, multicentre study of external ventricular drainage-related infections in the UK and Ireland.

OBJECTIVES: External ventricular drain (EVD) insertion is a common neurosurgical procedure. EVD-related infection (ERI) is a major complication that can lead to morbidity and mortality. In this study, we aimed to establish a national ERI rate in the UK and Ireland and determine key factors influencing the infection risk. METHODS: A prospective multicentre cohort study of EVD insertions in 21 neurosurgical units was performed over 6 months. The primary outcome measure was 30-day ERI. A Cox regression model was used for multivariate analysis to calculate HR. RESULTS: A total of 495 EVD catheters were inserted into 452 patients with EVDs remaining in situ for 4700 days (median 8 days; IQR 4-13). Of the catheters inserted, 188 (38%) were antibiotic-impregnated, 161 (32.5%) were plain and 146 (29.5%) were silver-bearing. A total of 46 ERIs occurred giving an infection risk of 9.3%. Cox regression analysis demonstrated that factors independently associated with increased infection risk included duration of EVD placement for ≥8 days (HR=2.47 (1.12-5.45); p=0.03), regular sampling (daily sampling (HR=4.73 (1.28-17.42), p=0.02) and alternate day sampling (HR=5.28 (2.25-12.38); p<0.01). There was no association between catheter type or tunnelling distance and ERI. CONCLUSIONS: In the UK and Ireland, the ERI rate was 9.3% during the study period. The study demonstrated that EVDs left in situ for ≥8 days and those sampled more frequently were associated with a higher risk of infection. Importantly, the study showed no significant difference in ERI risk between different catheter types.

A web-based survey to identify current practice in skeletal pin site management.

Infections associated with percutaneous pins and wires are common complications which can have a significant impact on patient outcomes. A survey was undertaken to identify current practice and gain insight into variations of clinical practice. Invitations were sent by email to complete an electronic questionnaire using SurveyMonkey. The survey was left open for 100 days. The single largest group of respondents (37.4%, n = 120) cleansed pin sites daily, with significant differences identified between medical and nursing professions (P = 0.02), and country of practice (P < 0.001). Significant differences were also identified in the use of different cleansing solutions between medical and nursing professions (P < 0.001) and country (P < 0.001). The majority group preferences were saline 30% (n = 96) and alcoholic chlorhexidine 29.6% (n = 95). Pin site crusts were routinely removed by 57.9% (n = 186). Pin sites were left exposed by 50.3% (n = 160). Dry gauze was identified as the most common dressing used to dress pin sites, however, substantial variation was identified in the types of dressings used. Compression was not routinely applied to pin sites by 51.6% (n = 165). There remains considerable diversity of practice when caring for pin sites. Further research is required to identify the most effective methods in preventing pin site infection.

Evaluation of combinations of putative anti-biofilm agents and antibiotics to eradicate biofilms of Staphylococcus aureus and Pseudomonas aeruginosa.

Objectives: To evaluate potential anti-biofilm agents for their ability to enhance the activity of antibiotics for local treatment of localized biofilm infections. Methods: Staphylococcus aureus and Pseudomonas aeruginosa in vitro biofilm models were developed. The putative antibiotic enhancers N-acetylcysteine, acetylsalicylic acid, sodium salicylate, recombinant human deoxyribonuclease I, dispersin B, hydrogen peroxide and Johnson's Baby Shampoo (JBS) were tested for their anti-biofilm activity alone and their ability to enhance the activity of antibiotics for 7 or 14 days, against 5 day old biofilms. The antibiotic enhancers were paired with rifampicin and clindamycin against S. aureus and gentamicin and ciprofloxacin against P. aeruginosa. Isolates from biofilms that were not eradicated were tested for antibiotic resistance. Results: Antibiotic levels 10× MIC and 100× MIC significantly reduced biofilm, but did not consistently eradicate it. Antibiotics at 100× MIC with 10% JBS for 14 days was the only treatment to eradicate both staphylococcal and pseudomonal biofilms. Recombinant human deoxyribonuclease I significantly reduced staphylococcal biofilm. Emergence of resistance of surviving isolates was minimal and was often associated with the small colony variant phenotype. Conclusions: JBS enhanced the activity of antibiotics and several other promising anti-biofilm agents were identified. Antibiotics with 10% JBS eradicated biofilms produced by both organisms. Such combinations might be useful in local treatment of localized biofilm infections.

A Three-Dimensional Model of Bacterial Biofilms and Its Use in Antimicrobial Susceptibility Testing.

(1) Background: The discrepant antimicrobial susceptibility between planktonic and biofilm bacterial modes poses a problem for clinical microbiology laboratories and necessitates a relevant 3D experimental model allowing bacteria to grow in biofilm mode, in vitro, for use in anti-biofilm susceptibility testing. (2) Methods: This work develops a 3D biofilm model consisting of alginate beads containing S. aureus biofilm and encased within two thick layers of alginate matrix. The constructed model was placed on a thin Boyden chamber insert suspended on a 24-well culture plate containing the culture medium. The antibacterial activity of bacitracin and chlorhexidine digluconate (CD), either combined or separately, against 2D S. aureus culture was compared to that in the 3D biofilm model. Quantitative analysis and imaging analysis were performed by assessing the bacterial load within the matrix as well as measuring the optical density of the culture medium nourishing the matrix. (3) Results: The 3D biofilm model represented the typical complex characteristics of biofilm with greater insusceptibility to the tested antimicrobials than the 2D culture. Only bacitracin and CD in combination at 100× the concentration found to be successful against 2D culture were able to completely eliminate the 3D biofilm matrix. (4) Conclusions: The 3D biofilm model, designed to be more clinically relevant, exhibits higher antimicrobial insusceptibility than the 2D culture, demonstrating that the model might be useful for testing and discovering new antimicrobial therapies. The data also support the view that combination therapy might be the optimal approach to combat biofilm infections.

Potential clinical value of catheters impregnated with antimicrobials for the prevention of infections associated with peritoneal dialysis.

INTRODUCTION: Peritoneal dialysis (PD) is a widely used dialysis modality, which offers the advantage of being a home therapy but is associated with a risk of potentially serious infections, including exit site infection, catheter tunnel infection, and peritonitis that may result in morbidity, technique failure, and increased mortality. Catheters impregnated with antimicrobials hold promise as a novel technique to reduce PD associated infections. AREAS COVERED: We describe PD modalities, catheters, technique, complications, and the microbiology of associated infections, as well as standard measures to reduce the risk of infection. A novel technique for the impregnation of silicone devices with antimicrobial agents has been used to produce antimicrobial impregnated ventricular shunt catheters with proven clinical efficacy that have now been adopted as the standard of care to reduce neurosurgical infections. Using the same technology, we have developed PD and urinary catheters impregnated with sparfloxacin, triclosan, and rifampicin. Safety and tolerability have been demonstrated in urinary catheters, and a similar study is planned in PD catheters. EXPERT OPINION: Catheters impregnated with antimicrobials offer a simple technique to reduce PD associated infections and thereby enable more people to enjoy the advantages of PD. Clinical trials are needed to establish efficacy.

Peritoneal dialysis (PD) is a type of treatment for kidney failure. To perform PD, a silicone tube is placed in the abdomen and the other end exits through the skin. Fluid is run into the abdomen via the tube and then drained out again after 1­12 hours. This process is repeated multiple times per day. Toxins and other waste chemicals normally removed by the kidneys enter the fluid, while it is in the abdomen and are then removed from the body when the fluid is drained out. In this way, PD partially replaces kidney function. Sometimes bacteria get into the tube, and this can cause serious infections in the abdomen. At present, measures available to prevent PD tube infections include careful hygiene when handling the tube, application of antibiotic creams or ointments to the exit site or treatment with antibiotics at the time of medical procedures that may increase infection risk. Despite these measures, peritonitis (abdominal infection) is one of the most common causes of people having to stop PD and change to another form of dialysis that involves direct filtration of the blood (hemodialysis). Frequent use of antibiotics may also cause the bacteria that cause peritonitis to become resistant to antibiotics. There is, therefore, an urgent need to develop new ways to prevent PD tube infections. Tubes have been used in patients who have a particular type of brain surgery with antibiotics introduced into the material that the tube is made from, and in these patients, the risk of infection has been reduced by 60­80%. The same technology is also being tested for urine tubes that are placed in the bladder and tubes used for PD. These urine tubes and PD tubes need further testing to establish safety and effectiveness. Though our experience with them leads us to expect that they are safe, the authorities that control new drugs and devices require us to show this beyond doubt before they can be introduced into routine care.

Action of linezolid or vancomycin on biofilms in ventriculoperitoneal shunts in vitro.

Cerebrospinal fluid (CSF) shunts used to treat hydrocephalus have an overall infection rate of about 10% of operations. The commonest causative bacteria are Staphylococcus epidermidis, followed by Staphylococcus aureus and enterococci. Major difficulties are encountered with nonsurgical treatment due to biofilm development in the shunt tubing and inability to achieve sufficiently high CSF drug levels by intravenous administration. Recently, three cases of S. epidermidis CSF shunt infection have been treated by intravenous linezolid without surgical shunt removal, and we therefore investigated vancomycin and linezolid against biofilms of these bacteria in vitro. A continuous-perfusion model of shunt catheter biofilms was used to establish mature (1-week) biofilms of Staphylococcus aureus, Staphylococcus epidermidis (both methicillin resistant [MRSA and MRSE]), Enterococcus faecalis, and Enterococcus faecium. They were then "treated" with either vancomycin or linezolid in concentrations achievable in CSF for 14 days. The biofilms were then monitored for 1 week for eradication and for regrowth. Enterococcal biofilms were not eradicated by either vancomycin or linezolid. Staphylococcal biofilms were eradicated by both antibiotics after 2 days and did not regrow. No resistance was seen. Linezolid at concentrations achievable by intravenous or oral administration was able to eradicate biofilms of both S. epidermidis (MRSE) and S. aureus (MRSA). Neither vancomycin at concentrations achievable by intrathecal administration nor linezolid was able to eradicate enterococcal biofilms. It is hoped that these in vitro results will stimulate further clinical trials with linezolid, avoiding surgical shunt removal.

Ventriculoperitoneal shunt-related infections caused by Staphylococcus epidermidis: pathogenesis and implications for treatment.

The insertion of medical devices, such as intraventricular shunts, is often complicated by infection leading to ventriculitis. Frequently, such infections result from colonisation and subsequent biofilm formation on the surfaces of the shunts by Staphylococcus epidermidis. The pathogenesis of neurosurgical shunt-related infection is complex with interactions between the pathogen, the device and the unique local immunological environment of the central nervous system (CNS). An ability to form biofilm, the main virulence determinant of Staphylococcus epidermidis, facilitates protection of the organism from the host defences while still initiating an immunological response. The presence of the blood brain barrier (BBB) and the biofilm itself also complicates treatment, which presents many challenges when managing shunt infections. A greater understanding of the interplay between S. epidermidis and the CNS could potentially improve the diagnosis, treatment and management of such infections. This review describes the pathogenesis, treatment and implications of S. epidermidis ventriculoperitoneal shunt-related infections, concentrating on recent research and the implications for treatment.

Self-targeting of zwitterion-based platforms for nano-antimicrobials and nanocarriers.

Self-targeting antimicrobial platforms have yielded new possibilities for the treatment of infectious biofilms. Self-targeting involves stealth transport through the blood circulation towards an infectious biofilm, where the antimicrobial platform penetrates and accumulates in a biofilm in response to a change in environmental conditions, such as local pH. In a final step, nano-antimicrobials need to be activated or the antimicrobial cargo of nanocarriers released. Zwitterions possess both cationic and anionic groups, allowing full reversal in zeta potential from below to above zero in response to a change in environmental conditions. Electrolyte-based platforms generally do not have the ability to change their zeta potentials from below to above zero. Zwitterions for use in self-targeting platforms are usually hydrophilic and have a negative charge under physiological conditions (pH 7.4) providing low adsorption of proteins and assisting blood circulation. However, near or in the acidic environment of a biofilm, they become positively-charged yielding targeting, penetration and accumulation in the biofilm through electrostatic double-layer attraction to negatively-charged bacteria. Response-times to pH changes vary, depending on the way the zwitterion or electrolyte is built in a platform. Self-targeting zwitterion-based platforms with a short response-time in vitro yield different accumulation kinetics in abdominal biofilms in living mice than platforms with a longer response-time. In vivo experiments in mice also proved that self-targeting, pH-responsive zwitterion-based platforms provide a feasible approach for clinical control of bacterial infections. Clinically however, also other conditions than infection may yield an acidic environment. Therefore, it remains to be seen whether pH is a sufficiently unique recognition sign to direct self-targeting platforms to an infectious biofilm or whether (additional) external targeting through e.g. near-infrared irradiation or magnetic field application is needed.

Using a comprehensive audit to identify local context prior to care bundle design and implementation for inadvertent perioperative hypothermia in colorectal surgery.

BACKGROUND: The first step in bundle design or implementation is to identify the problem being addressed. Several validated approaches are recommended to facilitate this. These include using systematic reviews, adverse event triggers and risk assessment tools. However, these methods do not fully take the local context into account, which will limit the effectiveness of the bundle. AIM: This study explores the potential benefit of using a comprehensive audit to identify an organisation's local context prior to designing and implementing a care bundle. METHOD: A comprehensive audit comprising observations of four patient journeys, interviews with 21 staff and clinical data was carried out at one large National Health Service trust in England. A patient warming care bundle was used as the exemplar. FINDINGS: Each of the three data collection methods identified specific local practices which would be addressed within the planning and implementation stages of a care bundle. These practices would not have been identified through other recommended methods. CONCLUSION: A comprehensive audit, comprising observations, interviews and clinical data is a successful method to identify local contextual issues prior to care bundle implementation.

Activity of an antimicrobial hydrocephalus shunt catheter against Propionibacterium acnes.

Shunt infection is a major complication affecting approximately 10% of procedures. Propionibacterium acnes, an anaerobic skin bacterium, is increasingly recognized as a shunt pathogen, causing up to 14% of infections. Though susceptible to penicillin and cephalosporins, P. acnes shunt infections are not preventable by means of perioperative prophylaxis, due to poor cerebrospinal fluid penetration. Antimicrobial shunts with activity against staphylococci are available, but their activity against P. acnes is unknown, and the study was designed to determine this. Three methods of evaluation were used in order to determine the emergence of resistance when exposure is to high inocula for long periods, the time taken to kill 100% of the bacteria attached to the shunt, and the duration of activity under constant flow conditions with repeated bacterial challenge. Despite repeated exposure to high bacterial inocula over 70 days, no resistance was seen. The time taken to kill all attached bacteria, 96 h, was twice that taken to kill attached staphylococci. Nevertheless, under constant flow conditions with repeated challenges, the antimicrobial catheters resisted colonization by P. acnes for 56 days. Using tests that were designed to be clinically predictive when done together, the results suggest that the antimicrobial catheters will be able to prevent colonization of hydrocephalus shunts by P. acnes.

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.