The efficacy of silver dressings and antibiotics on MRSA and MSSA isolated from burn patients

Abstract

In this study our objectives were (1) to investigate whether meticillin-resistant Staphylococcus aureus (MRSA) showed an increased tolerance to silver wound dressings compared with meticillin-sensitive S. aureus (MSSA); and (2) to evaluate the effects of bacterial phenotypic states of MRSA and MSSA, and pH, on the activity of silver wound dressings and two antibiotics, ampicillin and clindamycin. Twenty MRSA strains and 10 MSSA strains isolated from burns patients in South Africa were evaluated for their susceptibility to a silver alginate and a silver carboxymethyl cellulose wound dressing, employing a corrected zone of inhibition assay, conducted on Mueller Hinton agar and a poloxamer-based biofilm model. When exposed to the two silver dressings, all 30 S. aureus strains showed susceptibility. Possible enhanced antimicrobial efficacy of the silver dressings occurred when pH was lowered to 5.5, compared with a pH of 7.0. When all S. aureus were grown in the biofilm phenotypic state and exposed to both silver dressings and antibiotics, enhanced tolerance was noted. Susceptibility to silver was overall higher for MRSA when compared with MSSA. This study showed that the effect of pH and bacterial phenotypic state must be considered when the antimicrobial activity of silver wound dressings is being investigated. It is evident from the data generated that both pH and the bacterial phenotypic state are factors that induce changes that affect both antimicrobial performance and bacterial susceptibility.

Silver and Alginates: Role in Wound Healing and Biofilm Control

“…44 In this study the objectives were to investigate whether MRSA demonstrated an increased tolerance to silver wound dressings compared with MSSA and to evaluate the effects of bacterial phenotypic states of MRSA and MSSA, and pH, on the activity of silver wound dressings and two antibiotics, ampicillin and clindamycin. Twenty MRSA and 10 MSSA isolates from burns patients in South Africa were evaluated for their susceptibility to a silver alginate and a silver carboxy methyl cellulose wound dressing, employing a CZOI assay, conducted on Mueller Hinton agar (MHA) and a poloxamer-based biofilm model.…”

The increased killing of biofilms in vitro by combining topical silver dressings with topical negative pressure in chronic wounds

“…A variety of silver forms exist are powders, foams, hydrocolloids, hydrogels, polymeric films and meshes. When in solution, reactive silver ions (Ag + ) are formed and induce toxicity to many of the structural components of the bacterial cell wall, and biochemical pathways such as the respiratory cytochromes, and DNA and RNA alterations to prevent transcription and cellular division (30). The results are more complex for the members of the staphylococcal group that remain a significant contributor to chronic wounds.…”

“…In the literature, there is little evidence for the development of silver resistance; so we investigated the potential of combining a biofilm disrupting technology with a chemical silver treatment. Experimental work by KCI (27) has shown a consistent release of non-ionic silver particles from the silver foam for the first 72 hours (29). We, therefore, compared the efficacy of silver foam and black foam with and without concurrent TNP treatment at 3 days.…”

In Vitro Assessment of the Antibacterial Potential of Silver Nano-Coatings on Cotton Gauzes for Prevention of Wound Infections

“…Silver plays an important role in the management of burn wounds by reducing the microbial growth within a wound dressing and wound bed. The antimicrobial properties of silver-impregnated wound dressings against Gram-positive and Gram-negative bacteria have been demonstrated in several in vivo studies [14,15,16]. …”