Technology update Evaluation of low-adherent antimicrobial dressings
of foams A and B were observed to be relatively flat [Figures 6a and 6b respectively], whereas foam C was observed to have a more undulating surface, with visible raised rims around each perforation [Figures 4c and 6c respectively]. The adhesives all appeared to have some hydrophobic properties and were also observed to be a barrier to liquid water (data not shown). Elemental analysis (EDX elemental maps
and spectra not shown) of the SEM samples indicated that silver was associated with all of the fibres in the HF-Ag dressing and to be evenly distributed. Silver was also detected on a significant proportion of the fibres within the AL-Ag dressing, but there was no observable evidence of silver associated with the non-adherent sleeve areas [Figure 3b]. For the foam dressings, no silver was detected or associated with the WSCL, it was only observed in the foam portion of the dressing. The WSCL adhesive components of foams A and C were observed to contain significant amounts of silicone; this element was not observed to
be present in the adhesive layer of foam B, suggesting this was a different type of adhesive.
Seeded-agar microbial model The seeded-agar layer of the negative control plates (no dressing) appeared opaque and contained confluent bacteria growth [Figure 7]. Stab cultures taken from this seeded layer yielded heavy growth, thus confirming the viability of both S. aureus and P. aeruginosa over the test period. Table 3 summarises the bacteriostatic and bactericidal properties of the dressings tested. At the end of the initial 48-hour dressing
contact period and after a further 24 hours incubation of the plate with the dressing removed, the area that had been in contact with the HF-Ag dressing remained transparent and no bacterial colonies were observed [Figures 8a and 8c]. Negligible growth of S. aureus was observed with AL-Ag [Figures 9a and 9c]. Stab cultures of the HF-Ag plates produced no growth on DEA (indicating bactericidal activity), whereas growth was
Figure 10. Observed effect of foam A dressing on aS. aureus (A) andP. aeruginosa (C) simulated colonised wound surface after a 48-hour contact period. Heavy bacterial growth was visually observed beneath the position where the dressing had been applied (A and C). Similarly, heavy growth was observed of S. aureus (B) andP. aeruginosa (D) growth was observed upon the respectively removed foam A dressings after the 48-hour contact period.
A B
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1. The seeded layer of negative control plates yielded heavy growth, thus confirming the viability of bothS. aureus andP. aeruginosa
2. No bacterial colonies were observed in the HF-Ag dressing
3. Negligible growth ofS. aureus was observed with AL-Ag
C
D
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