The effects of pH on wound healing, biofilms, and antimicrobial efficacy.

It is known that pH has a role to play in wound healing. In particular, pH has been shown to affect matrix metalloproteinase activity, tissue inhibitors of matrix metalloproteinases activity, fibroblast activity, keratinocyte proliferation, microbial proliferation, and also immunological responses in a wound; the patient's defense mechanisms change the local pH of a wound to effect microorganism invasion and proliferation; this pH change has been found to affect the performance of antimicrobials, and therefore the efficacy in biological environments directly relevant to wound healing. Based on the available body of scientific evidence to date, it is clear that pH has a role to play in both the healing of and treatment of chronic and acute wounds. It is the purpose of this review to evaluate the published knowledge base that concerns the effect of pH changes, the role it plays in wound healing and biofilm formation, and how it can affect treatment efficacy and wound management strategies.

Silver resistance in MRSA isolated from wound and nasal sources in humans and animals.

Methicillin-resistant Staphylococcus aureus (MRSA) colonises skin, nasal passages and dermal wounds. Methods used to manage wounds infected and colonised with MRSA often include the use of topical antiseptics such as ionic silver and iodine. The objectives of this study were to determine the prevalence of silver-resistance (sil) genes in MRSA and methicillin-resistant coagulase-negative staphylococci (MR-CNS) isolated from wounds and nasal cavities of humans and animals, and also to determine the susceptibility of sil-positive and sil-negative MRSA isolates to a silver-containing Hydrofiber (SCH) wound dressing, on planktonic silE-positive and silE-negative MRSA. Polymerase chain reaction was used to determine the presence of three silver-resistance (sil) genes, silE, silP and silS in 33 MRSA and 8 methicillin-resistant staphylococci (MR-CNS). SilP and silS genes were absent in all isolates tested; however, two MRSA strains were found to contain the silE gene, together with one isolate of MR-CNS. Phenotypic resistance of the silE-positive strains and their susceptibility to the SCH dressing was evaluated using the zone of inhibition test on Mueller Hinton agar, and confocal laser microscopy using a live/dead fluorescent stain. Results confirmed that the SCH dressing was effective in killing all MRSA strains with and without the silE gene. First, this study showed that the prevalence of sil genes was low in the isolates investigated; and secondly, that the presence of a silver-resistance gene (silE) in MRSA and MR-CNS did not afford protection to the organism in the presence of a SCH wound dressing. The use of topical antiseptics in chronic wound care should be considered before the use of antibiotics that can result in their overuse and the risk of further resistance.

Assessing the effect of an antimicrobial wound dressing on biofilms.

To date the effect of silver-containing wound dressings on biofilms, known to be present in chronic wounds, has not been determined or documented. In this current study, we aimed to determine the antimicrobial effect of a silver-containing dressing on biofilms grown in a chambered slide model. Before the addition of a wound dressing onto a 24-hour biofilm, composed of either Pseudomonas aeruginosa, Enterobacter cloacae, Staphylococcus aureus, or a mixed bacterial community, a fluorescent dye was applied. This enabled the viability of sessile bacteria to be monitored in real-time, using a rapid form of confocal laser scanning microscopy over a contact time period of 48 hours. By analyzing all the three-dimensional data generated from the confocal time-lapse sequences, 90% of all sessile bacteria within the biofilm were observed to progressively turn red (i.e., died) within 24 hours. Total bacterial kill in the biofilm was achieved after 48 hours. This research has shown that the dressing was effective in killing the tested bacteria evident in both the tested mono and polymicrobial biofilms, which provides valuable evidence that this dressing may have an effect on biofilms found in recalcitrant chronic wounds.