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Laboratory Research
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Prevalence of silver resistant bacteria isolated from chronic wounds Steven Percival, PhD, Moses K. Nutekpor , Jayne Dolman, Philip G. Bowler, Christine A. Cochrane, ConvaTec Wound Therapeutics, Deeside, Flintshire, UK Concerns associated with the overuse of silver and the subsequent emergence of bacterial resistance are now being expressed in wound care. Consequently the aim of this study was to determine if silver-resistant bacteria are associated with chronic wounds and assess the prevalence of silver resistance genes in these isolates. A collection of 140 clinical isolates obtained from chronic wounds were used in this study. Investigations for silver resistant genes were carried out by polymerase chain reaction (PCR). Attempts were made to screen a gene from each of the three transcriptional units of the silver resistance system, namely silE, and silS and silP were also selected. Positive controls consisted of recombinant clones of E. coli (J53) containing fragments of PMG101 plasmid. A partial Sau3AI library of pMG101 was constructed in the BamHI site of pUC19 to obtain pKM1 plasmid with ampicillin marker and cloned into E. coli DH5a, which showed partial resistance to Ag+. The fragment of the PMG101 plasmid contained silS and silE genes, hence these were used as positive controls. For silP gene, an EcoRI digest in the EcoRI site of pUC19 (pKM3) with ampicillin marker was cloned into E. coli DH5a and used as the positive control. Plasmid preparations of the cloned E. coli served as a second positive control. E. coli J53 without a plasmid was used as the negative control for all the genes. Two isolates were identified as being sil positive. Both isolates were identified as Enterobacter cloacae and found to be positive for silP, silE and silS. To date, silver resistance appears to be more prevalent in enteric bacteria that are not recognised as wound pathogens. |
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