Download Antimicrobial Treatments for Silicones Medical Silicone Conference

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