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Antimicrobial Treatments for Silicones K. Mark Wiencek, Ph.D. Senior Microbiologist Milliken & Company Medical Silicone Conference November, 2010 Healthcare-Acquired Infections (HAIs) • 1.7 Million Healthcare-acquired Infections in USA per year1 • 5% of hospitalized patients develop HAI1 • Nearly 100,000 deaths estimated1 • > 5 Billion $ in extra costs1 • New reporting rules require hospitals to disclose infection rates • Medicare no longer reimburses hospitals for costs of HAIs • Most common HAIs2 (many are medical-device related) – – – – 1Klevens Urinary tract infections (32%) Surgical site infections (22%) Catheter-related blood stream infections (14%) Ventilator-associated pneumonia (15%) Public Health Report 2007 2”Antimicrobial Resistance in Healthcare Settings”, CDC online, 2002 What Causes Medical Device-Related Infections (MDRIs)? • Microbes! – Bacteria are leading cause of infections – Fungi (yeast) are second • Microbes from – Patient’s own body – Other bodies – Environment (fomites) • Some common bad actors: – Staphylococcus epidermidis – Serratia marcescens – Staphylococcus aureus – Pseudomonas aeruginosa – Candida albicans (yeast) – Escherichia coli – Enterococcus faecalis – Klebsiella pneumoniae But…it’s also how these microbes live → Biofilm is... • The growth of microbes on a surface • Common names: mildew, scum, plaque and slime – usually mixture of species and types of microbes – complex structure of channels, pores and clusters – requires moisture, food and time – involves cell-cell communication SURFACE Biofilms and “Resistance” • Encasement of cells within biofilm matrix limits diffusion of antimicrobials – Makes biofilms “inherently resistant” liquid surface liquid surface • Some cells exposed to sub-lethal concentrations of antimicrobial – Can lead to development of “acquired resistance” – MRSA, VRE, growing list of others Biofilms and Silicone • Microbes only need a bit of moisture to survive (days, weeks) – No biofilm, but can be transferred while surviving (cross contamination) • Microbes need moisture and food and time to grow and reproduce • Silicones themselves fairly inert – Nutrients from silicone processing aids? – More likely that microbes grow on soiling/organic residues on the silicone • Silicone applications – Medical devices (implants, catheters, IV connectors, respiratory therapy) – Tubing (beverage, dental) Biofilms on Silicone Medical Devices Biofilm on and in catheters Biofilm in luer access device Candida (yeast) biofilm on silicone voice box prosthesis CPAP / Ventilator Masks • Microbes and Health Issues – Skin – Respiratory • Compliance Issues (CPAP) – CPAPs can be challenging to clean properly – Microbes cause foul odors and staining – Users don’t…use Artificial Airway Ventilator Circuit HEPA Filter Heated Humidifier CPAP Masks • • • CPAP equipment collected from fellow associates and families Silicone components rinsed in 50ml buffer; filtered 10ml onto membrane filters Filters placed onto differential media; incubated up to 5 days at 30°C The Cleanest TSA (~bacteria) SDA (~fungi) McKY (~ Gram - bacteria) MSA (~ “Staph”) The Dirtiest TSA (~bacteria) SDA (~fungi) McKY (~ Gram - bacteria) MSA (~ “Staph”) Contamination Isolated from CPAP Masks TSA (~bacteria) SDA (~fungi) McKY (~ Gram - bacteria) MSA (~ “Staph”) Unique – Only 1-2 species recovered (1 yeast, 1 mold) from CPAP mask (swab) BEFORE CLEANING TSA (~bacteria) SDA (~fungi) AFTER CLEANING TSA (~bacteria) SDA (~fungi) Antimicrobials Antimicrobials for Plastics and Rubber Organics Triclosan CHG Quat-silanes Inorganics PHMB Copper Antibiotics Zinc Silver Silver Ion Silver Metal Silver-Based Antimicrobials Ag Silver Metal Silver Ion Silver Salt Coated or Absorbed Ion Exchange Systems Supported Silicaaluminates Zeolites Ag/Zn zeolite Ag/Zn/ NH4+ zeolite SiO2-Al203 On SiO2 Ag Thiosulfate On SiO2 Phosphates Ag, Ca, PO4 Soluble Glass AgCI on TiO2 Ag2O, P205, MgO, CaO, B2O3 Ag, H, Zr, PO4 Silver Coated Substrates Ag on TiO2 SelectSilver® SR12 SelectSilver® Zr2k Nano Silver Ag on Fibers or Fabrics Organic vs. Inorganic Advantages Disadvantages Cheaper than inorganics Poor thermo-, chemical stability Migration/Blooming allows most of antimicrobial to reach surface Rapid migration may lead to premature depletion on shelf or use Some organic AMs not as sensitive to soiling as silver Poor biocompatibility Potentially less impact on discoloration and clarity than inorganic Limited spectrum of activity against microbes (eg triclosan) May be easier to disperse within silicon matrix or apply topically May increase risk of resistance (eg antibiotics) Inorganic (silver) vs. Organic Advantages Disadvantages Thermostability Cost Carrier of silver ion or silver metal does not migrate, so reservoir is preserved Silver ions are only available to release from surface or bulk that is accessed by moisture Biocompatible; accepted by FDA and clinicians Negative effects on color and clarity of resin Efficacy against broad range of microbes (esp. among bacteria) Relatively weak against fungi (yeast and mold) compared to bacteria Resistance to silver extremely rare Zeolites and other Inorganic “Sponges” Silver ZrP (eg SelectSilver® Zr2k) Cl-Zr2-(PO4)3-Ag PO4Cl- NaCl Na+ Ag+ Ag+ Ag2Cl3AgCl2- AgCl Ag+ Silver salts, Silver metal (nanoAg) nano silver silver salt (AgCl) Ag+ Ag+ ClAg+ H20 Ag2Cl3AgCl2- Ag+ AgCl Silver Glasses Silver Glass (eg SelectSilver® SR12) Ag+ Ag+ Cl- 10µm Ag+ H20 Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag+ Ag2Cl3AgCl2- What Happens Next? bind 3Ag+ Silver bindsions to and and inactivate inactivates proteins proteins inside cell inside cells S Mg Cl silver ions will bind to proteins 2 Some + Some Ag proteins and andwill saltsbind in theto medium (food) and salts in the local environment become inactivated 1 Ag+ released from treated article Silver ions are released from Antimicrobial Alphasan® embedded in surface of substratum FLOW Ag+ released inside some polymers can discolor proteins in the medium (food) and Antimicrobial Performance of Silver in LSR Evaluation of Silver Antimicrobials in LSR • Injection molded coupons with different doses of SelectSilver SR12 (silver-based antimicrobial) – SR12 contains ca. 2% w/w of silver ions – Dose level range (1.5 - 15% of SR12) • Concentration of antimicrobial in LSR – X-Ray Fluorescence • Release of silver from treated LSR over time • Efficacy against microbes – Reduction in viable bacteria in 24hr with “Film-Contact Assay” Silver Antimicrobials and LSR • Determining Dose of Silver-based Antimicrobials in LSR – Normal process of ashing/digesting matrix very difficult with LSR – X-Ray Fluorescence Spectroscopy (XRF) can be used to detect silver • Or signature element for carrier of silver XRF Counts for Ag (- untreated) – Must establish calibration curves with known dose of antimicrobial 4000 y = 314.08x 2 R = 0.9364 3500 CM 3000 2500 y = 348.39x 2 R = 0.994 IM 2000 1500 1000 500 0 0 2 4 6 8 Target Dose of SR 12 (%) 10 12 Silver – Speed of Kill • Release of silver ions from treated LSR – Measure released silver with Induction Coupled Plasma Optical Emission Spectrometry (ICP-OES) 15% SR12 (exp 2) 10% SR12 10% SR12 (exp 2) 5% SR12 500 Silver Release (ppb) – Soak treated coupons in saline or buffer Short-Term Release of Silver into Saline 600 400 300 200 100 0 0 • Speed of Kill related to Rate of silver release 4 8 12 Time (hours) 16 20 24 Speed of Kill • Silver-treated Wound Dressings • Topical application of high loadings of silver (1-2%) • Several hours required for silver ion to reach efficacious level, enter microbes, inactivate enzymes and…kill Efficacy of Silver Dressings Against MRSA Untreated Gauze AFM Ag Acticoat 7 Efficacy of Silver Dressings Against P. aeruginosa 8 Aquacel Ag No. of Viable Cells (Log CFU/Dressing) No. Viable Cells (log CFU/dressing) 8 7 6 5 4 3 2 1 0 0 4 8 12 Time (Hours) 16 20 24 7 6 Untreated Gauze AFM Ag Acticoat 7 Aquacel Ag 5 4 3 2 1 0 0 4 8 12 Time (Hours) 16 20 24 Silver Release over Days • For most devices, extended release is more critical than fast release • Repeated exposures to fluids will (eventually) deplete antimicrobial from surface • Release in saline (with no nutrients) often results in equilibrium of Ag+ with AgCl at 400-500ppb Ag • Release rate from SR12-treated LSR often increases after material is wetted • Different silver-based antimicrobials can behave quite differently Release of Silver through Repeated Exposures to Saline Silver Released (ppb) 500 400 300 7% SR12 (0.14% Ag) 200 10% Zr2k (1.0% Ag) 100 0 0 1 2 3 4 5 6 Days of Exposure 7 8 9 10 Why Doesn’t Zr2k Work Well in LSR? Surface of LSR Cross-section of LSR • LSR loaded with 20% silver hydrogen zirconium phosphate (cubic particles) • Scanning electron microscopy of surface vs. cross section of bulk material • Evidence that most particles on surface are covered by silicone (“skinning”) 40 mm “Film Contact” JIS Z 2801 ISO 22196 AATCC 100, JIS L 1902, ISO 20743 MIC / MBC ISO 846 (fungi) Shake Flask ASTM E2149 TTC StainTest Agar Inoculum ASTM 2180 ZOI AATCC 147 Qualitative 40 mm Quantitative Test Methods (for Screening) Film Contact Method JIS Z 2801, ISO 22196 Method for hydrophobic, non-porous materials 10 ml of wash solution (for deactivation and cell recovery) 0.4 ml of bacterial suspension (~1 x 106 cells/ml) in saline with nutrients 40 mm 40 mm Cover with 4 x 4 cm film Results are compared vs. T0 and or Untreated Control Enumerate # of Survivors with Serial Dilution + Spread/Pour Plate or Alternative Methods (eg MPN) 40 mm 40 mm 37ºC, o/n, static, 90% RH Efficacy of SR12-treated LSR Efficacy of Antimicrobial SR 12 in Saline + Nutrient Broth Efficacy of LSR Treated with SelectSilver SR12 Untreated LSR Untreated Injection-Molded LSR K. pneumoniae S. aureus K. pneumoniae S. aureus 1.5% SR 12 5% SR 12 1.5% (no pre-exposure) 7% SR 12 5% (no pre-exposure) 10% SR 12 10% (no pre-exposure) 1.5% SR 12 (3 day exposure) 1.5% (3d pre-exposure) 5% SR 12 (3 day exposure) 5% (3d pre-exposure) 7% SR 12 (3 day exposure) 10% (3d pre-exposure) 10% SR 12 (3 day exposure) 1.5% (7d pre-exposure) 1.5% SR 12 (7 day exposure) 5% (7d pre-exposure) 5% SR 12 (7 day exposure) 10% (7d pre-exposure) 7% SR 12 (7 day exposure) 10% SR 12 (7 day exposure) Maximum Log Reduction Maximum Log Reduction 0 1 2 3 4 Log Reduction vs. Untreated Polypropylene Control 5 6 0 1 2 3 4 5 Log Reduction vs. Untreated PP Control • Efficacy by Film-Contact Method; 24hr exposure at 37°C in saline + nutrients • As with silver release, efficacy sometimes increases after material exposed to moisture • As with all silver-based antimicrobials, efficacy against Gram negative bacteria often higher than against Gram positive bacteria 6 Effects of Post-Curing Efficacy of SR 12 in LSR K. pneumoniae Untreated Si Control (no post cure) S. aureus No post cure 5% SR 12 (Day 0) 10% SR 12 (Day 0) 5% SR 12 (Day 7) 10% SR 12 (Day 7) post cured Untreated Si Control (post cure) 5% SR 12 (Day 0) 10% SR 12 (Day 0) 5% SR 12 (Day 7) 10% SR 12 (Day 7) Maximum Log Reduction 0 1 2 3 4 5 6 7 Log Reduction (vs. Internal Control) • Post-curing does not appear to impact antimicrobial performance in vitro Test Methods and FDA Registration • Must test safety and efficacy of antimicrobial treatment in medical device – Safety = Biocompatibility – Efficacy = Reduction of microbes • Testing for registration must be conducted on the actual device, or in few circumstances, just the treated components of device • FDA issued draft guidelines for Antimicrobials in Devices (2007) – Primarily concerned with path forward if new antimicrobial agent vs. previously approved agent – http://www.fda.gov/MedicalDevices/DeviceRegulationandGuidance/Guidance Documents/ucm071380.htm • FDA also has changed the types of data that are acceptable – Quantitative reduction (so, no ZOI data) – In most cases, require ≥4 log reduction – In most cases, require initial bioburden (inoculum) of ≥106 cells Regulation of Antimicrobial-Treated Materials • Medical Devices – Regulated by FDA and EU Medical Device Directive • “Treated Articles” (AlphaSan® RC2000, RC5000) – Pesticidal use regulated by USA-EPA and BPD – Claims restricted to material preservation and aesthetic benefits • No public health claims – Cannot claim activity beyond treated surface – Restricted to use levels on EPA label Resistance and Tolerance to Antimicrobials • Acquired Resistance: The effect of a given concentration of antimicrobial is diminished due to genetic change within the microbe (that affects target access) • Resistance to Biocides << Resistance to Antibiotics Biocides (most) → non-specific target = ⇓ rate and degree of resistance Antibiotics → specific target = ⇑ rate and degree of resistance • Multitude of cellular targets for silver, other anaseptics Difficult for selection for resistance by target change as with antibiotics The mechanism of action is critical to understand resistance and tolerance How to Reduce MDRIs? • Use of an antimicrobial agent may appear to be the sole missing ingredient to solve MRDI problems • However, go to conferences like APIC, meet with OEMs and IC Professionals, and one gets the feeling: – 70-80% reduction through better hygiene – 10-20% through device design and composition – Leaving perhaps 10-20% through use of antimicrobial additive