The increasing threat of silver-resistance in clinical isolates from wounds and burns

Infection and Drug Resistance Dovepress open access to scientific and medical research Infection and Drug Resistance downloaded from https://www.dovepress.com/ by 88.198.20.149 on 28-Sep-2019 For personal use only. Open Access Full Text Article ORIGINAL RESEARCH The increasing threat of silver-resistance in clinical isolates from wounds and burns This article was published in the following Dove Press journal: Infection and Drug Resistance Alaa El-Dien MS Hosny 1 Salwa A Rasmy 1 Dina S Aboul-Magd 2 Mona T Kashef 1 Zeinab E El-Bazza 2 1 Microbiology and Immunology Department, Faculty of Pharmacy, Cairo University, Cairo, Egypt; 2Drug Radiation Research Department, National Center for Radiation Research and Technology, Atomic Energy Authority, Cairo, Egypt Purpose: The widespread use of silver-containing compounds has led to emergence of silver-resistant bacteria. Few studies are available on the detectability of plasmid-mediated silver-resistance in developing countries. Therefore, we aimed to detect silver-resistance in isolates from wounds and burns, and to genetically characterize plasmid-mediated silverresistance genes (sil genes). Methods: One hundred and fifty clinical isolates were obtained from burns and wounds. They were identified using the suitable Analytical Profile Index and MicroScan identification systems. Their antimicrobial susceptibility was tested by the disk diffusion and broth microdilution methods. Their silver nitrate (AgNO3) minimum inhibitory concentration (MIC) was determined using the broth macrodilution method. The presence of different sil genes on plasmids extracted from silver-resistant isolates and the replicon types of the extracted plasmids were investigated using polymerase chain reaction (PCR). The ability of these plasmids to impart silver-resistance was tested by transformation. Results: All except two isolates were multidrug-resistant. Nineteen silver-resistant bacterial isolates (12.6%) were detected; with AgNO3 MIC ≥512 µg/mL. They were identified as Klebsiella pneumoniae (n=7), Staphylococcus aureus (n=4), Escherichia coli (n=2), Enterobacter cloacae (n=2), Pseudomonas aeruginosa (n=2) and Acinetobacter baumannii (n=2). PCR revealed the presence of different sil genes on the extracted plasmids. Plasmid transformation resulted in the transfer of silver-resistance to the resulting transformants. The extracted plasmids had different replicon types. Conclusion: Plasmid-mediated silver-resistance was detected for the first time, in clinical P. aeruginosa, A. baumannii and S. aureus isolates; in addition to its detection in K. pneumoniae, E. coli and Enterobacter cloacae. Therefore, strict monitoring on the use of silver compounds in medical settings is required; with implementation of an approved standardized method for silver-resistance detection. Keywords: multidrug-resistance, plasmid-mediated, replicon type, sil genes Introduction Correspondence: Mona T Kashef Department of Microbiology and Immunology, Faculty of Pharmacy, Cairo University, Kasr El-Eini St, Cairo 11562, Egypt Tel +2 022 363 9307 Fax +2 022 362 8426 Email 1985 submit your manuscript | www.dovepress.com Infection and Drug Resistance 2019:12 1985–2001 DovePress © 2019 Hosny et al. This work is published and licensed by Dove Medical Press Limited. The full terms of this license are available at https://www.dovepress.com/terms. php and incorporate the Creative Commons Attribution – Non Commercial (unported, v3.0) License (http://creativecommons.org/licenses/by-nc/3.0/). By accessing the work you hereby accept the Terms. Non-commercial uses of the work are permitted without any further permission from Dove Medical Press Limited, provided the work is properly attributed. For permission for commercial use of this work, please see paragraphs 4.2 and 5 of our Terms (https://www.dovepress.com/terms.php). http://doi.org/10.2147/IDR.S209881 Powered by TCPDF (www.tcpdf.org) The silver cation (Ag+) has been employed long ago as an antimicrobial agent (eg, AgNO3 solution and silver sulfadiazine cream), for its microbicidal properties, minimum toxicity to human cells and therapeutic activity; especially in the prevention and treatment of burns and chronic wounds infections.1 Silver ions cause respiration inhibition, membrane damage and destruction of the proton motive force in sensitive organisms; through their interaction with thiol groups present in membrane proteins or enzymes and consequently the respiratory chain enzymes.2 It can also generate reactive oxygen species that interfere with DNA replication3 and increase membrane permeability.4 Dovepress Infection and Drug Resistance downloaded from https://www.dovepress.com/ by 88.198.20.149 on 28-Sep-2019 For personal use only. Hosny et al Silver-impregnated dressings and antimicrobial coatings are used in infection management and stimulation of wound healing.5,6 Also, silver is used as a component in dental amalgam and silver-impregnated medical devices, such as catheters and heart valves.7 The widespread and uncontrolled use of silver may result in increasing the rate of bacterial resistance to silver-containing compounds where silver-resistant bacteria are as problematic as antibiotic-resistant ones.8 Acquired silver-resistance can be of endogenous (mutational) or exogenous (horizontally acquired) origin. Endogenous resistance to silver in Gram-negative bacteria can arise from derepression of the chromosomal Cus system and loss of outer membrane porins.9,10 Also, derepression of the expression of silver-resistance genes (sil genes), integrated into Escherichia coli chromosome, has been reported to result in silver-resistance after stepwise adaptation in laboratory.11 Staehlin and colleagues12 have described a heavy metal homeostasis/resistance island, named as Copper homeostasis and silver resistance island (CHASRI), which was assembled and dispersed within members of Enterobacteriaceae family. Recently, CHASRI was found to be equally distributed in the plasmids and chromosomes of Enterobacteriaceae and was able to provide silver-resistance after mutation in CusS and/or silS genes of the CHASRI island.13 Exogenous silver-resistance was documented to be due to acquisition plasmid-encoded sil system.14,15 The first encountered exogenous (horizontally acquired) silver-resistance was detected in a bacterial strain of Salmonella enterica serovar Typhimurium that caused an outbreak on a burns ward in 1975; causing the death of three patients.16 Later, this resistance phenotype was detected in other bacterial species.17,18 The first described plasmid was isolated from this Salmonella strain and named pMG101. The silver-resistance determinant comprises nine Open Reading Frames (ORFs) defining three transcriptional units (silE, silS, silR, silC, silF, silB, silA, ORF105 and silP).8 These acquired silver-resistance genes are usually located on plasmids of the incompatibility group HI2 (IncHI2).19 Silver-resistance, whethe (...truncated)