Samantha Jones, PgDip, BSc Sarah Welsby, BSc David Parsons PhD, MRSC CChem

1. A new anti-biofilm dressing:
in vitro determination of microbial kill rate
in biofilms
Samantha Jones, PgDip, BSc
Sarah Welsby, BSc
David Parsons PhD, MRSC CChem
ConvaTec Research and Development, Flintshire, Wales, UK
EP475
1EWMA 2013 Poster EP475
© 2023 ConvaTec Inc.
©/TM AQUACEL and Hydrofiber are trade marks of ConvaTec Inc..
All other trade marks are the property of their respective owners.

2. Introduction
• In their natural habitat, most bacteria exist in bacterial communities encapsulated in a
gelatinous extracellular polymeric substance (EPS) which is attached to a surface. This is
known as biofilm.1
• Biofilm EPS is produced by the bacteria and serves as a protective niche for survival. It
renders them more resistant to the host immune response and antimicrobial therapies
alike.1,2
• Bacterial biofilm is increasingly recognised as being a barrier to wound healing and there
is a growing evidence that biofilms are a cause of wound chronicity1,2,3 – with studies
demonstrating biofilm prevalence of at least 60%.3
• Therefore, to be clinically useful, antimicrobial therapies must be effective against
biofilm.
•This poster describes in-vitro studies used to measure the anti-biofilm properties of a
new custom designed absorbent antimicrobial antibiofilm dressing (EASH).
2EWMA 2013 Poster EP475
1. Bjarnsholt T. (2013). The Role of Bacterial Biofilms in Chronic Infections. APMIS 121 (Suppl. 136): 1–51
2. Metcalf D.G. & Bowler P.G. (2013). Biofilm delays wound healing: A review of the evidence. Burns Trauma 1 Epub.
3. James G.A., Swogger E., Wolcott R., et al. (2008). Biofilms in chronic wounds. Wound Rep Reg 16, 37-44.

3. Materials & Methods
3EWMA 2013 Poster EP475
Study 1
Biofilms were grown on sterile cotton gauzes by immersion in a bacteria-
containing simulated wound fluid at 35°C for ≥ 48 hours. Gauzes were then
rinsed with isotonic saline to remove any unattached bacteria. The presence
of biofilm was confirmed by scanning electron microscopy (SEM). Biofilm-
loaded gauzes were exposed to test dressings hydrated with isotonic saline for
4, 24 and 48 hours at 35°C. Bacterial bioburden was determined by processing
the gauzes in a neutralizing diluent and then assaying by standard
microbiological techniques.
Study 2
Biofilms were prepared as in study 1, then a PHMB-containing gauze was
applied for a further 48 hours to eliminate any planktonic cells whilst
maintaining growth of a predominately biofilm population. EASH dressing
samples were then applied hydrated with simulated wound fluid and
incubated at 35°C for up to 96 hours. Quantitative analysis was performed as
previously described.
Coding Material Product Manufacturer
EASH Enhanced silver-containing Hydrofiber AQUACEL®Ag+ ConvaTec
SH Silver-containing Hydrofiber AQUACEL®Ag ConvaTec
H Hydrofiber AQUACEL® ConvaTec
PHMB-Gauze
Polyhexamethylene biguanide-containing
non-adherent gauze
TelfaTMAMD Covidien
Challenge Organism Study
Pseudomonas aeruginosa
(NCIMB 8626)
1
Staphylococcus aureus
(NCIMB 9518)
1
Candida albicans
(NCPF 3179)
1
Pseudomonas aeruginosa
(wild type strain PA01)
2

4. Results – confirming the presence of biofilm
4EWMA 2013 Poster EP475
P. aeruginosa
NCIMB 8626
S. aureus
NCIMB 8626
C. albicans NCPF 3179
P. aeruginosa PA01
(after application of a PHMB-containing gauze)

5. Results – Biofilm eradication (Study 1)
5EWMA 2013 Poster EP475
30
300
3.000
30.000
300.000
3.000.000
30.000.000
300.000.000
3.000.000.000
0 12 24 36 48
ViableBacteria(cfu)
Dressing Contact Time (hours)
S.aureus EASH SH H
(Limit of Detection)
30
300
3.000
30.000
300.000
3.000.000
30.000.000
300.000.000
3.000.000.000
0 12 24 36 48
ViableBacteria(cfu)
Dressing Contact Time (hours)
P.aeruginosa
(Limit of Detection)
30
300
3.000
30.000
300.000
3.000.000
30.000.000
300.000.000
3.000.000.000
0 12 24 36 48
ViableBacteria(cfu)
Dressing Contact Time (hours)
C.albicans
(Limit of Detection)

6. Results – Biofilm eradication (Study 2)
6EWMA 2013 Poster EP475
30
300
3.000
30.000
300.000
3.000.000
30.000.000
300.000.000
3.000.000.000
0 24 48 72 96
ViableBacteria(cfu)
Dressing Exposure Time (hours)
P.aeruginosa (wild type PA01)
EASH
PHMB-Gauze
H
Limit of Detection →

7. In-vitro anti-biofilm dressing study: Summary
• Three potential wound pathogens were shown to form dense
biofilm on cotton gauze (Staphylococcus aureus, Pseudomonas aeruginosa
and Candida albicans)
• Biofilm forms of each potential pathogen were tolerant to
two antimicrobial dressings
• Biofilm forms of each potential pathogen were highly
susceptible to an anti-biofilm dressing (EASH†)
– bacterial counts fell below the limit of detection within 48 hours
– approximately an 8 log reduction (100 million-fold) in each case
– >3 log reduction being achieved within 4 hours for S.aureus and P. aeruginosa
7EWMA 2013 Poster EP475† AQUACEL®Ag+