Waheed Ashraf

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.

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.

Prevention of infection in neurosurgery: role of “antimicrobial” catheters

Catheters are used in neurosurgery mainly forcerebrospinal fluid (CSF) drainage, taking the formof either shunts or external ventricular drainage(EVD) devices. While approximately 4000 shuntsare inserted each year in the UK (UK ShuntRegistry, unpublished data), numbers are notavailable for EVDs but they are certainly higher.CSF shunts are used for permanent managementof intracranial pressure in hydrocephalus, whileEVDs are used for short-term (2 3 days to 2 3weeks) management of intracranial pressure dueto subarachnoid haemorrhage, trauma, tumoursor infection. In each case, infection is a seriouscomplication associated with poor outcome.Totallyinternal devices such as shunts are classified asCategory 1 devices, whereas EVDs are partiallyimplanted and are therefore Category 2 devices

Action of Linezolid or Vancomycin on Biofilms in Ventriculoperitoneal Shunts In Vitro

ABSTRACT 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.

Biofilm Eradication With Biodegradable Modified-Release Antibiotic Pellets A Potential Treatment for Glue Ear

OBJECTIVE To develop a biodegradable, modified-release antibiotic pellet capable of eradicating biofilms as a potential novel treatment for biofilm infections. DESIGN Pellets containing poly(DL-lactic-co-glycolic acid) microparticles, rifampin and clindamycin hydrochloride (3.5%, 7%, or 28% antibiotic by weight), and carrier gel (carboxymethylcellulose or poloxamer 407) were tested in vitro. Drug release was assessed using serial plate transfer testing and high-performance liquid chromatography, and pellets were tested against biofilms in an in vitro model of Staphylococcus aureus biofilm grown on silicone. RESULTS Serial plate transfer testing demonstrated continuing bacterial inhibition for up to 21 days for all pellets studied. High-performance liquid chromatography showed high levels of drug release for 2 to 4 days, with greatly reduced levels subsequently; continued measurable clindamycin (but not rifampin) release for up to 21 days was achieved. Pellets made with poloxamer released higher drug levels for a longer period. Irrespective of the carrier gel used, pellets containing 7% and 28% (but not 3.5%) antibiotic eradicated biofilms successfully. CONCLUSIONS Antibiotic pellets can release antibiotics for up to 21 days and are able to eradicate biofilms in an in vitro model. Use of modified-release antibiotic formulations in the middle ear as a treatment for biofilms appears to be a potentially promising new therapy for otitis media with effusion.

Activity of an Antimicrobial Hydrocephalus Shunt Catheter against Propionibacterium acnes

ABSTRACT 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.

An in vitro investigation of the antimicrobial activity of silver-processed catheters for external ventricular drainage

Background Ventriculitis is a serious complication of external ventricular drainage (EVD). Silver-processed catheters (S-PC) are available that are intended to reduce the risk of infection. Clinical results of use of S-PC in other settings have been mixed, with benefit limited to only short-term use [1,2]. Little clinical experience of S-PC for EVD use [3], and no in-depth laboratory studies have been reported. We therefore examined the catheters to determine their antimicrobial activity in clinically relevant tests.

The development of an antimicrobial EVD catheter to protect against multi-resistant hospital “superbugs”

Background External Ventricular Drainage (EVD) infections are a serious complication, and the period of risk extends until the device is removed. The causative bacteria of EVD and shunt infections are similar but there are more multi – resistant strains such as MRSA and gram negative bacteria in EVD infections, particularly when the patient is in intensive care. To counter this, we have development an antimicrobial EVD catheter with a broad spectrum to protect against these multi-resistant bacteria. Thus, the aim of this study was to evaluate the antimicrobial activity of this catheter against multiresistant Staphylococcus epidermidis, MRSA, and gram negatives using clinically predictive in vitro tests. Materials and methods Medical grade silicone catheter tubing (Codman) was impregnated with antimicrobials: 1% triclosan, 1% trimethoprim and 0.2% rifampicin respectively. Three methods were used to evaluate the antimicrobial activity of the catheter. The Serial Plate Transfer Test (SPTT) is a screening test for duration of antimicrobial activity and to monitor resistance. Impregnated catheter segments were placed onto agar plates seeded with bacteria and incubated. Segments were removed daily and placed on fresh plates and reincubated. The inhibition zone was measured across the short axis. This was repeated until no inhibition zones were seen. The time taken to kill 100% of bacteria attached to catheter segments (tK100), was determined by first coating the catheter segments with a protein conditioning film, then allowing the bacteria to adhere to plain and antimicrobial catheter segments and incubating them. Samples were retrieved daily, sonicated to remove the adherent bacteria, and the sonicate cultured quantitatively to detect bacterial growth. Thirdly, a simulated in vitro model was used to determine the ability of the antimicrobial catheter to resist successive bacterial challenges every 14 days under constant perfusion, designed to mimic the CSF flow. Results

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.

Does release of antimicrobial agents from impregnated external ventricular drainage catheters affect the diagnosis of ventriculitis

OBJECTIVE Recently concern has arisen over the effect of released antimicrobial agents from antibiotic-impregnated external ventricular drainage (EVD) catheters on the reliability of CSF culture for diagnosis of ventriculitis. The authors designed a laboratory study to investigate this possibility, and to determine whether there was also a risk of loss of bacterial viability when CSF samples were delayed in transport to the laboratory. METHODS Three types of commercially available antibiotic-impregnated EVD catheters were perfused with a suspension of bacteria (Staphylococcus epidermidis) over 21 days. Samples were analyzed for bacterial viability and for concentrations of antibiotics released from the catheters. The authors also investigated the effect on bacterial viability in samples stored at 18°C and 4°C to simulate delay in CSF samples reaching the laboratory for analysis. RESULTS Bacterial viability was significantly reduced in all 3 catheter types when sampled on Day 1, but this effect was not observed in later samples. The results were reflected in stored samples, with significant loss of viability in Day 1 samples but with little further loss of viable bacteria in samples obtained after this time point. All samples stored for 18 hours showed significant loss of viable bacteria. CONCLUSIONS While there were differences between the catheters, only samples taken on Day 1 showed a significant reduction in the numbers of viable bacteria after passing through the catheters. This reduction coincided with higher concentrations of antimicrobial agents in the first few hours after perfusion began. Similarly, bacterial viability declined significantly after storage of Day 1 samples, but only slightly in samples obtained thereafter. The results indicate that drugs released from these antimicrobial catheters are unlikely to affect the diagnosis of ventriculitis, as sampling for this purpose is not usually conducted in the first 24 hours of EVD.