Effects of silver on adherence of bacteria to urinary catheters: in vitro studies

Modulation of Quorum Sensing and Biofilms in Less Investigated Gram-Negative ESKAPE Pathogens

Pathogenic bacteria have the ability to sense their versatile environment and adapt by behavioral changes both to the external reservoirs and the infected host, which, in response to microbial colonization, mobilizes equally sophisticated anti-infectious strategies. One of the most important adaptive processes is the ability of pathogenic bacteria to turn from the free, floating, or planktonic state to the adherent one and to develop biofilms on alive and inert substrata; this social lifestyle, based on very complex communication networks, namely, the quorum sensing (QS) and response system, confers them an increased phenotypic or behavioral resistance to different stress factors, including host defense mechanisms and antibiotics. As a consequence, biofilm infections can be difficult to diagnose and treat, requiring complex multidrug therapeutic regimens, which often fail to resolve the infection. One of the most promising avenues for discovering novel and efficient antibiofilm strategies is targeting individual cells and their QS mechanisms. A huge amount of data related to the inhibition of QS and biofilm formation in pathogenic bacteria have been obtained using the well-established gram-positive Staphylococcus aureus and gram-negative Pseudomonas aeruginosa models. The purpose of this paper was to revise the progress on the development of antibiofilm and anti-QS strategies in the less investigated gram-negative ESKAPE pathogens Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter sp. and identify promising leads for the therapeutic management of these clinically significant and highly resistant opportunistic pathogens.

Evaluation of central venous catheters coated with a noble metal alloy-A randomized clinical pilot study of coating durability, performance and tolerability

The use of Central Venous Catheters (CVCs) commonly results in complications. Coatings with silver or metal alloys can reduce the risk associated with the use of CVC. We have evaluated the durability of a noble metal coated CVC (the Bactiguard Infectious Protection, BIP CVC) and compared with an uncoated CVC for clinical tolerability (Adverse Events, AEs) and performance, in order to create a baseline for a large future study. Patients undergoing major surgery, randomised at a 2:1 ratio to BIP CVC (n = 22) or standard CVC (n = 12), were catheterized 9 ‐ 12 days, respectively. Adverse events, microbial colonization and metal release were measured.

Findings: There were no AEs in the BIP CVC‐group, but 5 AEs occurred in 4 patients (1 patient had 2 AEs) in the standard CVC‐group, p = 0.011 (whereof 3 were catheter related). The BIP CVC showed an initial release of coating metals in blood (gold, silver and palladium), which rapidly decreased and were far below Permitted Paily Exposure (PDE) for chronical use. The levels of silver concentration were far below those needed to develop microbial resistance. The performance was equal, and there was no difference concerning microbial colonization, for the two CVCs.

Conclusion: In this pilot study the BIP CVC had significantly lower AEs and showed a comparable performance to the standard CVC. The coating was durable throughout the study length (up to 16 days) and toxicological evaluation showed good safety margins. Larger studies are needed. © 2017 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 106B: 2337–2344, 2018.

Improved ex vivo blood compatibility of central venous catheter with noble metal alloy coating

Central line associated bloodstream infections (CLABSIs) are a serious cause of morbidity and mortality induced by the use of central venous catheters (CVCs). Nobel metal alloy (NMA) coating is an advanced surface modification that prevents microbial adhesion and growth on catheters and thereby reduces the risk of infection. In vitro microbiological analyses have shown up to 90% reduction in microbial adhesion on coated CVC compared to uncoated ones. This study aimed to assess the blood compatibility of NMA-coated CVC according to ISO 10993-4. Hemolysis, thrombin-antithrombin (TAT) complex, platelet counts, fibrin deposition, and C3a and SC5b-9 complement activation were analyzed in human blood exposed to the NMA-coated and control CVCs using a Chandler-loop model. NMA-coated CVC did not induce hemolysis and fell in the "nonhemolytic" category according to ASTM F756-00. Significantly lower amounts of TAT were generated and less fibrin was deposited on NMA-coated CVC than on uncoated ones. Slightly higher platelet counts and lower complement markers were observed for NMA-coated CVC compared to uncoated ones. These data suggest that the NMA-coated CVC has better ex vivo blood compatibility compared to uncoated CVC. © 2015 The Authors Journal of Biomedical Materials Research Part B: Applied Biomaterials Published by Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1359-1365, 2016.

Tolerability and performance of BIP endotracheal tubes with noble metal alloy coating--a randomized clinical evaluation study

Background

Hospital acquired infections worsen the outcome of patients treated in intensive care units and are costly. Coatings with silver or metal alloys may reduce or alter the formation of biofilm on invasive medical devices. An endotracheal tube (ETT) is used to connect the patient to a ventilator and coated tubes have been tested in relation to bacterial colonization and respiratory infection. In the present study, we aimed to evaluate and compare a coated and uncoated ETT for patient symptoms and local tracheal tolerability during short term clinical use. Degree of bacterial colonization was also described.

Methods

A silver-palladium-gold alloy coating (‘Bactiguard®’Infection Protection, BIP) has been extensively used on urinary tract catheters and lately also on central venous catheters. We performed a randomised, single-blinded, controlled, first in man, post Conformité Européenne (EC) certification and CE marking study, focused on Bactiguard® coated ETTs (BIP ETT). Thirty patients at a tertiary university hospital scheduled for upper abdominal elective surgery with an expected duration of anaesthesia of at least 3 h were randomised; BIP ETT (n = 20) or standard ETT (n = 10). The tolerability was assessed with a modified version of Quality of Life Head and Neck Module, QLQ-H&N35 and by inspection of the tracheal mucosa with a fibre-optic bronchoscope before intubation and at extubation. Adverse Events (AE) and bacterial adherence were also studied. Statistical evaluations were carried out with the Fisher’s Exact Test, the Clopper-Pearson method, as well as a Proportional Odds Model.

Results

Differences between groups were identified in 2 of 8 patient related symptoms with regard to tolerability by QLQ-H&N35 (cough, p = 0.022 and dry mouth, p = 0.014 in the treatment group.). No mucosal damage was identified with bronchoscopy. A low level of bacterial colonization with normal flora, equal between groups, was seen after short-term of intubation (median 5 h). No serious Adverse Events related to the use of an ETT were observed. The results should be treated with caution due to statistical confounders, a small study size and large inter-individual variability in bacterial adhesion.

Conclusions

The new device BIP ETT is well tolerated and has good clinical performance during short-term intubation. Studies with larger sample sizes and longer intubation periods (>24 h) in the ICU-setting are needed and can now be planned in order to identify possible differences in clinical outcomes.

Trial registration

Registered in ClinicalTrials.gov, Registration number: NCT01682486, Date of Registration: August, 30, 2012

Silver-coated endotracheal tubes for prevention of ventilator-associated pneumonia in critically ill patients

BACKGROUND

Ventilator-associated pneumonia (VAP) is one of the most common nosocomial infections in intubated and mechanically ventilated patients. Endotracheal tubes (ETTs) appear to be an independent risk factor for VAP. Silver-coated ETTs slowly release silver cations. It is these silver ions that appear to have a strong antimicrobial effect. Because of this antimicrobial effect of silver, silver-coated ETTs could be an effective intervention to prevent VAP in people who require mechanical ventilation for 24 hours or longer.

OBJECTIVES

Our primary objective was to investigate whether silver-coated ETTs are effective in reducing the risk of VAP and hospital mortality in comparison with standard non-coated ETTs in people who require mechanical ventilation for 24 hours or longer. Our secondary objective was to ascertain whether silver-coated ETTs are effective in reducing the following clinical outcomes: device-related adverse events, duration of intubation, length of hospital and intensive care unit (ICU) stay, costs, and time to VAP onset.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL; 2014 Issue 10, MEDLINE, EMBASE, EBSCO CINAHL, and reference lists of trials. We contacted corresponding authors for additional information and unpublished studies. We did not impose any restrictions on the basis of date of publication or language. The date of the last search was October 2014.

SELECTION CRITERIA

We included all randomized controlled trials (RCTs) and quasi-randomized trials that evaluated the effects of silver-coated ETTs or a combination of silver with any antimicrobial-coated ETTs with standard non-coated ETTs or with other antimicrobial-coated ETTs in critically ill people who required mechanical ventilation for 24 hours or longer. We also included studies that evaluated the cost-effectiveness of silver-coated ETTs or a combination of silver with any antimicrobial-coated ETTs.

DATA COLLECTION AND ANALYSIS

Two review authors (GT, HV) independently extracted the data and summarized study details from all included studies using the specially designed data extraction form. We used standard methodological procedures expected by The Cochrane Collaboration. We performed meta-analysis for outcomes when possible.

MAIN RESULTS

We found three eligible randomized controlled trials, with a total of 2081 participants. One of the three included studies did not mention the amount of participants and presented no outcome data. The 'Risk of bias' assessment indicated that there was a high risk of detection bias owing to lack of blinding of outcomes assessors, but we assessed all other domains to be at low risk of bias. Trial design and conduct were generally adequate, with the most common areas of weakness in blinding. The majority of participants were included in centres across North America. The mean age of participants ranged from 61 to 64 years, and the mean duration of intubation was between 3.2 and 7.7 days. One trial comparing silver-coated ETTs versus non-coated ETTs showed a statistically significant decrease in VAP in favour of the silver-coated ETT (1 RCT, 1509 participants; 4.8% versus 7.5%, risk ratio (RR) 0.64, 95% confidence interval (CI) 0.43 to 0.96; number needed to treat for an additional beneficial outcome (NNTB) = 37; low-quality evidence). The risk of VAP within 10 days of intubation was significantly lower with the silver-coated ETTs compared with non-coated ETTs (1 RCT, 1509 participants; 3.5% versus 6.7%, RR 0.51, 95% CI 0.31 to 0.82; NNTB = 32; low-quality evidence). Silver-coated ETT was associated with delayed time to VAP occurrence compared with non-coated ETT (1 RCT, 1509 participants; hazard ratio 0.55, 95% CI 0.37 to 0.84). The confidence intervals for the results of the following outcomes did not exclude potentially important differences with either treatment. There were no statistically significant differences between groups in hospital mortality (1 RCT, 1509 participants; 30.4% versus 26.6%, RR 1.09, 95% CI 0.93 to 1.29; low-quality evidence); device-related adverse events (2 RCTs, 2081 participants; RR 0.65, 95% CI 0.37 to 1.16; low-quality evidence); duration of intubation; and length of hospital and ICU stay. We found no clinical studies evaluating the cost-effectiveness of silver-coated ETTs.

AUTHORS' CONCLUSIONS

This review provides limited evidence that silver-coated ETT reduces the risk of VAP, especially during the first 10 days of mechanical ventilation.

A unique in vivo approach for investigating antimicrobial materials utilizing fistulated animals

Unique in vivo tests were conducted through the use of a fistulated ruminant, providing an ideal environment with a diverse and vibrant microbial community. Utilizing such a procedure can be especially invaluable for investigating the performance of antimicrobial materials related to human and animal related infections. In this pilot study, it is shown that the rumen of a fistulated animal provides an excellent live laboratory for assessing the properties of antimicrobial materials. We investigate microbial colonization onto model nanocomposites based on silver (Ag) nanoparticles at different concentrations into polydimethylsiloxane (PDMS). With implantable devices posing a major risk for hospital-acquired infections, the present study provides a viable solution to understand microbial colonization with the potential to reduce the incidence of infection through the introduction of Ag nanoparticles at the optimum concentrations. In vitro measurements were also conducted to show the validity of the approach. An optimal loading of 0.25 wt% Ag is found to show the greatest antimicrobial activity and observed through the in vivo tests to reduce the microbial diversity colonizing the surface.

Cost-Effectiveness Analysis of a Silver-Coated Endotracheal Tube to Reduce the Incidence of Ventilator-Associated Pneumonia

Objective.

To conduct a cost-effectiveness analysis of the economic outcomes of ventilator-associated pneumonia (VAP) prevention associated with silver-coated endotracheal tubes versus uncoated endotracheal tubes.

Design.

We used a simple decision model based on a hypothetical 1,000-patient cohort intubated with silver-coated or uncoated endotracheal tubes. The primary end point was marginal hospital savings per case of VAP prevented (savings from using silver-coated endotracheal tubes minus acquisition cost divided by number of VAP cases prevented).

Methods.

We followed each branch of the decision model to VAP or no VAP and conducted Monte Carlo simulations and sensitivity analyses. Inputs for VAP incidence, relative risk reduction, and hospital costs were derived from publicly available sources. Relative risk reduction was derived from the pivotal study of the silver-coated endotracheal tube.

Results.

In the base-case analysis, we reduced the pivotal study relative risk in incidence of microbiologically confirmed VAP in patients intubated ≥24 hours from 35.9% to 24%. Thus, 23 of 97 expected cases of VAP could be prevented with silver-coated endotracheal tubes. The savings per case of VAP prevented was $12,840 in the base case, with assumed marginal VAP cost of $16,620 and costs of $90.00 for coated and $2.00 for uncoated endotracheal tubes. Estimates were most sensitive to assumptions regarding VAP cost and relative risk reduction with silver-coated endotracheal tubes. Nonetheless, in multivariate sensitivity analyses, the silver-coated endotracheal tubes yielded persistent savings (95% confidence interval, $9,630-$16,356) per case of VAP prevented. With other base-case inputs held constant, breakeven cost for silver-coated endotracheal tubes was $388.

Conclusions.

The silver-coated endotracheal tube represents a strategy for preventing VAP that may yield hospital savings.

Respiratory therapy device modifications to prevent ventilator-associated pneumonia

PURPOSE OF REVIEW

Ventilator-associated pneumonia (VAP) is a controversial entity in the field of critical care. After years of research and significant efforts from regulatory agencies and hospitals, this complication is still frequently affecting mechanically ventilated patients, making VAP an active battleground for research. As a result, several preventive measures have recently been tested in experimental and clinical trials. Our interest is focused on those innovations related to the endotracheal tube (ETT).

RECENT FINDINGS

Four ETT-related VAP causative mechanisms are reviewed, together with different associated potential solutions. Technologies such as the subglottic secretion drainage and the Mucus Slurper have been studied to eliminate subglottic secretion pooling. Novel designs for the cuff and the management of its pressure may avoid leakage. Antimicrobial coatings can prevent endoluminal biofilm formation, whereas using an ETT cleaning device may also be beneficial. Finally, preserving the tracheal ciliary function will keep our best physiologic protection active.

SUMMARY

VAP prevention strategies are a continuously evolving field. Being able to identify the most valuable ideas needs a deep understanding of the disease pathophysiology. The role of the ETT is crucial and there is need for our standards of care to improve. This may soon be possible with newer technologies becoming increasingly available to clinicians.

Osseointegration of titanium with an antimicrobial nanostructured noble metal coating

Nanometer scale surface features on implants and prostheses can potentially be used to enhance osseointegration and may also add further functionalities, such as infection resistance, to the implant. In this study, a nanostructured noble metal coating consisting of palladium, gold and silver, never previously used in bone applications, was applied to machined titanium screws to evaluate osseointegration after 6 and 12 weeks in rabbit tibiae and femurs. Infection resistance was confirmed by in vitro adhesion test. A qualitatively and quantitatively similar in vivo bone response was observed for the coated and uncoated control screws, using histology, histomorphometry and electron microscopy. The bone-implant interface analysis revealed an extensive bone formation and direct bone-implant contact. These results demonstrate that the nanostructured noble metal coating with antimicrobial properties promotes osseointegration and may therefore be used to add extra implant functionality in the form of increased resistance to infection without the use of antibiotics.

FROM THE CLINICAL EDITOR

The authors of this paper demonstrate that nanostructured noble metal coating of implants and prostheses used in orthopedic procedures promotes osseointegration and may be used to add extra implant functionality in the form of increased resistance to infection without the use of antibiotics.

In vitro comparison of nitrofurazone- and silver alloy-coated foley catheters for contact-dependent and diffusible inhibition of urinary tract infection-associated microorganisms

Two marketed antimicrobial-coated Foley catheters were compared for in vitro diffusible and contact-dependent inhibition of 11 urinary tract infection-associated microorganisms in an adherence-biofilm assay. Nitrofurazone-coated catheters significantly outperformed silver alloy-coated catheters for inhibitory activity, according to both inoculum broth and catheter sonicate counts, whether compared directly or against the corresponding control catheters. Although inhibition waned with catheter preincubation in saline, some organisms were inhibited even after a 48-h catheter preincubation, especially by the nitrofurazone-coated catheter.

Quorum sensing in biofilms--how to destroy the bacterial citadels or their cohesion/power?

Biofilms or microbial communities formed by adherent and cohesive cells on cellular or inert substrata (like medical devices), are involved in ≈ 60% of all infections and characterized by moderate intensity symptoms, chronic evolution and resistance to antibiotics. Biofilms' pathogenicity, even of those formed by opportunistic microorganisms, is amplified by two major biofilm characteristics: 1) the increased resistance to antimicrobials; 2) the protection of cells against the host's defence mechanisms. The studies at the molecular level shown that the biofilms formation is controlled by cell-to-cell signalling mechanisms and the gene regulation during biofilm growth is due to the accumulation of signal molecules. In this regard, quorum sensing mechanism (QS) is defined as a cell-density dependent bacterial intercellular communication, involved in gene expression (e.g. virulence genes for exoenzymes, exopolysaccharides) and the consequent changed behaviour of biofilm's cells, including the resistance to stress conditions; this resistance is different of well known antibioresistance, being named phenotypical resistance or tolerance. Considering the differences in physiology and susceptibility to antibiotics of biofilm embedded bacteria, as well as their increased power against the host defence responses, there are necessary new strategies for prevention and therapy of biofilm associated infections. The dental plaque is a typical example of biofilm, involved in the ethiology of cariogenesis and periodontal diseases associated with local chronic inflammation and cytokines production. The genetical and phenotypical versatility of the biofilm's cells represent a challenge for discovering new methods of treatment and prevention of biofilm associated infections. A novel class of antibiofilm and antipathogenic therapeutics which are interfering with a new target - the QS pathway, not based on growth inhibition and called QS inhibitors, natural, with different origins or artificial, are now developing as an alternative to antibiotherapy.

In vitro activity of available antimicrobial coated Foley catheters against Escherichia coli, including strains resistant to extended spectrum cephalosporins

PURPOSE

We determined the activity, comparative potency and effect durability of commercially available, antimicrobial coated Foley catheters against Escherichia coli isolates, including extended spectrum cephalosporin resistant strains.

MATERIALS AND METHODS

We used an inhibition zone assay (diffusible inhibition) and an adherence assay (diffusible and contact dependent inhibition) to assess the inhibitory effect of 3 currently marketed antimicrobial coated catheters, including 2 coated with silver and 1 coated with nitrofurazone, and corresponding silicone catheters against 9 E. coli strains, including 7 extended spectrum cephalosporin resistant and 2 extended spectrum cephalosporin susceptible strains, and a Pseudomonas aeruginosa reference strain.

RESULTS

In each assay the nitrofurazone coated catheter showed the greatest and most durable (through day 5) inhibitory activity. This was comparable for extended spectrum cephalosporin resistant and extended spectrum cephalosporin susceptible E. coli strains but decreased or absent for the Pseudomonas strain. One of the 2 silver coated catheters showed sparse but measurable inhibition zone activity on day 1 but not thereafter and no statistically significant activity on adherence assay. The other lacked detectable activity using either test system. In the adherence assay the nitrofurazone coated catheter decreased the E. coli count as potently in inoculum broths as in post-sonication suspensions (median decrease more than 8 and more than 6 log(10) cfu/ml, respectively).

CONCLUSIONS

The nitrofurazone coated catheter showed significantly greater in vitro potency and durability of the antimicrobial effect against 9 E. coli strains than the 2 silver coated catheters, of which 1 appeared completely inert. No difference in antimicrobial effect was apparent between extended spectrum cephalosporin resistant and susceptible E. coli. The clinical relevance of these in vitro findings remains to be defined.

Molding a silver nanoparticle template on polydimethylsiloxane to efficiently capture mammalian cells

Herein, a functional template made up of in situ synthesized silver nanoparticles (AgNPs) is prepared on polydimethylsiloxane (PDMS) for the spatial control of cell capture, where the residual Si-H groups in the PDMS matrix are used as reductants to reduce AgNO(3) for forming AgNPs. In virtue of microfluidic system, a one-dimensional array pattern of AgNPs is obtained easily. Further combining with plasma treatment, a two-dimensional array pattern of AgNPs could be achieved. The obtained PDMS-AgNPs composite is characterized in detail. The PDMS-AgNPs composite shows good antibacterial property in E. coli adhesion tests. The patterns possess hifi and high resolution (ca. 8 microm). Cell patterns with high efficiency and spatial selectivity are further formed with the aid of H-Arg-Gly-Asp-Cys-OH (RGDC) tetrapeptide which is grafted on the AgNPs template. Cells immobilized on the template show a good ability for adhesion, spreading, migration, and growth.

Complicated catheter-associated urinary tract infections due to Escherichia coli and Proteus mirabilis

Catheter-associated urinary tract infections (CAUTIs) represent the most common type of nosocomial infection and are a major health concern due to the complications and frequent recurrence. These infections are often caused by Escherichia coli and Proteus mirabilis. Gram-negative bacterial species that cause CAUTIs express a number of virulence factors associated with adhesion, motility, biofilm formation, immunoavoidance, and nutrient acquisition as well as factors that cause damage to the host. These infections can be reduced by limiting catheter usage and ensuring that health care professionals correctly use closed-system Foley catheters. A number of novel approaches such as condom and suprapubic catheters, intermittent catheterization, new surfaces, catheters with antimicrobial agents, and probiotics have thus far met with limited success. While the diagnosis of symptomatic versus asymptomatic CAUTIs may be a contentious issue, it is generally agreed that once a catheterized patient is believed to have a symptomatic urinary tract infection, the catheter is removed if possible due to the high rate of relapse. Research focusing on the pathogenesis of CAUTIs will lead to a better understanding of the disease process and will subsequently lead to the development of new diagnosis, prevention, and treatment options.

Controlling biofilm formation with an N-halamine-based polymeric additive

An N-halamine-based polymeric additive, poly[(6-morpholino-s-triazine-2,4-diyl)-N-chloro-[2,2,6,6-tetramethyl-4-piperidyl)imino]-hexamethylene[(2,2,6,6-4-piperidyl) imino]] (APA-1), was prepared in this study. The chemical structure of APA-1 was confirmed by iodometric titration, (1)H NMR, and (13)C NMR analysis. APA-1 was incorporated into polyurethane through solvent casting. The resultant materials demonstrated potent antimicrobial functions against Staphylococcus epidermidis. Zone of inhibition studies showed that APA-1 inactivated the bacteria through contact, without leaching out of the polyurethane samples. In vitro studies illustrated that APA-1-containing polyurethane could prevent the colonization and biofilm formation of S. epidermidis for at least 28 days.

Reduced burden of bacterial airway colonization with a novel silver-coated endotracheal tube in a randomized multiple-center feasibility study*

OBJECTIVE

To assess the feasibility and safety of the respiratory infection control (RIC) device, a silver-coated endotracheal tube, and its effect on bacterial burden in the airways.

DESIGN

Prospective, randomized, single-blind, multiple-center study.

SETTING

Three hospitals in Spain and one in the United States.

PATIENTS

Patients were eligible adults who required mechanical ventilation for > or =24 hrs and did not have respiratory infections. One hundred forty-nine patients were intubated and analyzed for safety; 121 were intubated > or =24 hrs and analyzed for tube colonization; 67 had negative baseline quantitative endotracheal aspirates and were analyzed for quantitative endotracheal aspirates colonization.

INTERVENTIONS

Intubation with the RIC device or a control endotracheal tube.

MEASUREMENTS AND MAIN RESULTS

The RIC device was associated with delayed colonization on the tube compared with the control device at the threshold of ++, +++, or > or =10(4) colony-forming units/mL (p = .02, log-rank test; p = .10, Wilcoxon's test) and in quantitative endotracheal aspirates at > or =10(6) colony-forming units/mL (p = .08, log-rank test; p = .05, Wilcoxon's test). The RIC device was associated with reduced colonization rate by days on the tube (p = .04, Wilcoxon's test) and in quantitative endotracheal aspirates (p = .05, Wilcoxon's test) at the same thresholds. The RIC device was associated with lower maximal bacterial burden in tracheal aspirates for 7 days (mean log-transformed burden, 4.2 +/- 2.3 vs. 5.5 +/- 1.7 log colony-forming units/mL; p = .02, Wilcoxon's test). Other between-group differences favored the RIC device but were not significant. Five adverse events were considered device related, including three events in the RIC group and two events in the control group.

CONCLUSIONS

In this prospectively planned, preliminary analysis, the RIC device was feasible and well tolerated. Larger studies are needed to determine whether delayed colonization, reduced colonization rate, and decreased bacterial burden will decrease the incidence of ventilator-associated pneumonia.

Catheter-associated infections in urology: possible use of silver-impregnated catheters and the Erlanger silver catheter

Indwelling urinary catheters play a very important part in urology. However, their use is accompanied by a considerable increase in the risk of nosocomial urinary tract infections. The pathophysiological cause is ascribed to pathogens that adhere to the catheter surface, proliferate and produce a biofilm. In addition to aseptic techniques, modification of the catheter material to confer antimicrobial activity plays an essential part in the prevention of catheter-related urinary tract infections. The antimicrobial efficacy of silver against gram-positive and gram-negative bacteria is well known and amply shown in vitro. The efficacy of silver-impregnated catheters is critically dependent on both the chemical structure of the incorporated silver and the way the silver has been combined with the basic catheter material. Hence, clinical studies on silver-modified catheters have so far given inconsistent results. The new technology of the Erlanger silver catheter offers the opportunity of an effective reduction in catheter-related infections.

Efficacy of silver-coating central venous catheters in reducing bacterial colonization

OBJECTIVE

To compare silver-coated and uncoated central venous catheters regarding bacterial colonization. To assess the relative contribution of catheter hub and skin colonization to catheter tip colonization.

DESIGN

Prospective, randomized clinical trial.

SETTING

Intensive care unit in a university hospital.

PATIENTS

Patients after cardiac surgery who required a central venous double-lumen catheter (DLC).

INTERVENTIONS

Sixty-seven adult patients were prospectively randomized to receive either a silver-coated (S group, n = 34) or an uncoated control (C group, n = 33) DLC. Blood cultures were drawn at catheter removal, and removed catheters were analyzed with quantitative cultures. Typing of microorganisms included DNA fingerprinting.

MEASUREMENTS AND MAIN RESULTS

Catheters were removed if no longer necessary and aseptically divided into three segments: segment A, the catheter tip; segment B, an intermediate section; and segment C, the subcutaneous portion. Bacterial catheter colonization was quantitatively measured using sonication to detach adherent bacteria from the catheter segments in the broth and subsequent culture of an aliquot. Selected isolates of coagulase-negative staphylococci and other bacteria from catheter segments were examined by means of pulsed-field gel electrophoresis (PFGE) after macrorestriction digestion of bacterial DNA to study colonization pathogenesis. Quantitatively lower bacterial colonization could be demonstrated on the silver-coated catheters (200 +/- 550 colony forming units [CFUs]/cm catheter segment; mean +/- SD). The difference in the control catheters (1120 +/- 5350 CFUs/cm catheter segment; mean +/- SD) was not, however, significant (p = .25). The frequency of colonization of at least one catheter segment was 52.9% for the silver-coated catheters and 57.6% for the control catheters (p= .44), without any significant differences in the colonization of corresponding catheter segments. The rate of significant catheter colonization (i.e., > or = 10(3) CFUs/cm catheter by quantitative catheter culture or > or = 10(3) CFUs/mL by luminal flush) was nine in the silver group and seven in the control group, a difference that failed to reach significance (p = .41). Two patients in both groups developed catheter-related bacteremia. Pattern analysis after PFGE demonstrated that about 70% of the isolates found on the catheter tip were identical with those on the skin at the insertion site, whereas about 75% were identical with those recovered from the hub. In 29% of colonized catheters, identical bacteria were found on the hub and the skin at the insertion site.

CONCLUSIONS

Silver-coating of DLCs did not significantly reduce bacterial catheter colonization compared with the control catheters. PFGE analysis of coagulase-negative staphylococci and other bacteria demonstrated various pathogenic routes of catheter-related colonization, whereby the microorganisms of the skin flora around the insertion site must be regarded as the main source of catheter-related infections.

In vitro adherence of Pseudomonas aeruginosa to four intraocular lenses

PURPOSE

To compare the relative degrees of adherence of a clinical strain of Pseudomonas aeruginosa to the optic material of four intraocular lenses (IOLs).

SETTING

Center for Applied and Environmental Microbiology, Georgia State University, Atlanta, Georgia, USA.

METHODS

Intraocular lens optics made of poly(methyl methacrylate) (PMMA), AcrySof-acrylic, and silicone were included in this study. The IOLs were incubated in a minimal medium with cells of P. aeruginosa for 2 hours and 18 hours. Cells in the 2 hour experiment were prelabeled with 3H-leucine; those in the 18 hour experiments were postlabeled. After rinsing the IOLs to remove loosely adherent cells, we determined the number of cells adhered to coded lenses from calibration curves of disintegrations per minute versus cells per square millimeter. Additional lenses were incubated with P. aeruginosa and examined with scanning electron microscopy.

RESULTS

The adherence of P. aeruginosa in order of increasing magnitude was AcrySof-acrylic < PMMA < silicone 1 < silicone 2. The differences between all groups were statistically significant. The scanning electron microscopy observations were in general agreement with the radiolabel studies.

CONCLUSIONS

The AcrySof-acrylic IOL was less susceptible to primary adherence and 18 hour biofilm formation by P. aeruginosa than the PMMA and silicone IOLs, indicating that this material reduced pseudomonad adherence and the risk of endophthalmitis following cataract surgery.

Adherence of organisms to silver-coated surfaces

Pure silver-, silver oxide- and silver chloride-treated surfaces in comparison to polypropylene inhibited both growth and adherence from saline of Serratia marcescens, Staphylococcus epidermidis, Pseudomonas aeruginosa and Candida albicans. These same organisms demonstrated enhanced adherence to an Ion-Beam-Assisted-Deposited silver surface followed by loss of viability. This type of surface in contrast to the other silver surfaces did not produce zones of inhibition in agar diffusion tests.