title: 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.
authors.affiliation: Department of Pathology, Biofilm Laboratory, Medical School, West Virginia University, Morgantown, West Virginia, USA. steve.percival@admedsol.com
authors.forename: Steven L
authors.initials: SL
authors.lastname: Percival
authors.forename: John G
authors.initials: JG
authors.lastname: Thomas
authors.forename: Will
authors.initials: W
authors.lastname: Slone
authors.forename: Sara
authors.initials: S
authors.lastname: Linton
authors.forename: Linda
authors.initials: L
authors.lastname: Corum
authors.forename: Tyler
authors.initials: T
authors.lastname: Okel
mesh_terms: D000667:Ampicillin / Q000494:pharmacology; D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001458:Bandages; D018441:Biofilms; D002056:Burns / Q000382:microbiology*; D002981:Clindamycin / Q000494:pharmacology; D003470:Culture Media; D006801:Humans; D006863:Hydrogen-Ion Concentration; D066298:In Vitro Techniques; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification; D008826:Microbial Sensitivity Tests; D012834:Silver / Q000494:pharmacology*; D018030:Silver Compounds / Q000494:pharmacology; D013211:Staphylococcus aureus / Q000187:drug effects* / Q000302:isolation & purification
chemical_list: D000900:Anti-Bacterial Agents; D003470:Culture Media; D018030:Silver Compounds; D012834:Silver; D002981:Clindamycin; D000667:Ampicillin