Prevalence of silver resistance genes in bacteria isolated from human and horse wounds

Prevalence of silver resistance determinants and extended-spectrum β-lactamases in bacterial species causing wound infection: First report from Bangladesh

Background

The use of silver is rapidly rising in wound care and silver-containing dressings are widely used along with other antibiotics, particularly β-lactams. Consequently, concerns are being raised regarding the emergence of silver-resistance and cross-resistance to β-lactams. Therefore, this study aimed to determine the phenotypic and genotypic profiles of silver-resistance and extended-spectrum β-lactamases in isolates from chronic wounds.

Methods

317 wound swab specimens were collected from tertiary hospitals of Dhaka city and analysed for the microbial identification. The antibiotic resistance/susceptibility profiles were determined and phenotypes of silver resistant isolates were examined. The presence of silver-resistance (sil) genes (silE, silP, and silS) and extended-spectrum β-lactamases (ESBL) (CTX-M-1, NDM-1, KPC, OXA-48, and VIM-1) were explored in isolated microorganisms.

Results

A total of 501 strains were isolated with Staphylococcus aureus (24%) as the predominant organism. In 29% of the samples, polymicrobial infections were observed. A large proportion of Enterobacterales (59%) was resistant to carbapenems and a significantly high multiple antibiotic-resistance indexes (>0.2) were seen for 53% of organisms (P < 0.001). According to molecular analysis, the most prevalent types of ESBL and sil gene were CTX-M-1 (47%) and silE (42%), respectively. Furthermore, phenotypic silver-nitrate susceptibility testing showed significant minimum-inhibitory-concentration patterns between sil-negative and sil-positive isolates. We further observed co-occurrence of silver-resistance determinants and ESBLs (65%).

Conclusions

Notably, this is the first-time detection of silver-resistance along with its co-detection with ESBLs in Bangladesh. This research highlights the need for selecting appropriate treatment strategies and developing new alternative therapies to minimize microbial infection in wounds.

Unraveling the mechanisms of inhibition of silver-doped bioactive glass-ceramic particles

Infections are a major concern in orthopedics. Antibacterial agents such as silver ions are of great interest as broad-spectrum biocides and have been incorporated into bioactive glass-ceramic particles to control the release of ions within a therapeutic concentration and provide tissue regenerative properties. In this work, the antibacterial capabilities of silver-doped bioactive glass (Ag-BG) microparticles were explored to reveal the unedited mechanisms of inhibition against methicillin-resistant Staphylococcus aureus (MRSA). The antibacterial properties were not limited to the delivery of silver ions but rather a combination of antibacterial degradation by-products. For example, nano-sized debris punctured holes in bacteria membranes, osmotic effects, and reactive oxygen species causing oxidative stress and almost 40% of the inhibition. Upon successive Ag-BG treatments, MRSA underwent phenotypic and genomic mutations which were not only insufficient to develop resistance but instead, the clones became more sensitive as the treatment was re-delivered. Additionally, the unprecedented restorative functionality of Ag-BG allowed the effective use of antibiotics that MRSA resists. The synergy mechanism was mainly identified for combinations targeting cell-wall activity and their action was proven in biofilm-like and virulent conditions. Unraveling these mechanisms may offer new insights into how to tailor healthcare materials to prevent or debilitate infections and join the fight against antibiotic resistance in clinical cases.

Biocidal Activity of Tannic Acid-Prepared Silver Nanoparticles towards Pathogens Isolated from Patients with Exacerbations of Chronic Rhinosinusitis

The microbiome's significance in chronic rhinosinusitis (CRS) is unclear. Antimicrobials are recommended in acute exacerbations of the disease (AECRS). Increasing rates of antibiotic resistance have stimulated research on alternative therapeutic options, including silver nanoparticles (AgNPs). However, there are concerns regarding the safety of silver administration. The aim of this study was to assess the biological activity of tannic acid-prepared AgNPs (TA-AgNPs) towards sinonasal pathogens and nasal epithelial cells (HNEpC). The minimal inhibitory concentration (MIC) for pathogens isolated from patients with AECRS was approximated using the well diffusion method. The cytotoxicity of TA-AgNPswas evaluated using an MTT assay and trypan blue exclusion. A total of 48 clinical isolates and 4 reference strains were included in the study (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Klebsiella pneumoniae, Klebsiellaoxytoca, Acinetobacter baumannii, Serratia marcescens, Enterobacter cloacae). The results of the studies revealed that the MIC values differed between isolates, even within the same species. All the isolates were sensitive to TA-AgNPs in concentrations non-toxic to human cells during 24 h exposition. However, 48 h exposure to TA-AgNPs increased toxicity to HNEpC, narrowing their therapeutic window and enabling 19% of pathogens to resist the TA-AgNPs' biocidal action. It was concluded that TA-AgNPs are non-toxic for the investigated eukaryotic cells after short-term exposure and effective against most pathogens isolated from patients with AECRS, but sensitivity testing may be necessary before application.

Molecular characterization of resistance determinants and mobile genetic elements of ESBL producing multidrug-resistant bacteria from freshwater lakes in Kashmir, India

BACKGROUND

Antibiotic resistance conceded as a global concern is a phenomenon that emerged from the bacterial response to the extensive utilization of antimicrobials. The expansion of resistance determinants through horizontal transfer is linked with mobile genetic elements (MGEs) like transposons, insertion sequences, and integrons. Heavy metals also create consequential health hazards. Metal resistance gene in alliance with antibiotic resistance genes (ARGs) and MGEs is assisting bacteria to attain exalted quantity of resistance.

METHODOLOGY

The present work was carried out to study ARGs blaCTX-M, AmpC, qnrS, MGEs like ISecp1, TN3, TN21, and Int I by performing PCR and sequencing from Wular and Dal lakes of Kashmir; India. The genetic environment analysis of blaCTX-M-15 was carried out using PCR amplification, and sequencing approach followed by in-silico docking and mutational studies. Co-occurrence of ARGs and HMRGs was determined. Plasmid typing was done using PCR-based replicon typing (PBRT) and conjugation assay was also performed.

RESULTS

Out of 201 isolates attained from 16 locations, 33 were ESBLs producers. 30 ESBL displaying isolates were perceived positive for CTX-M gene, followed by AmpC (17), qnrS (13), ISecp1 (15), TN3 (11), TN21 (11), Int I (18), and SulI (14). The genetic environment of blaCTX-M-15 was observed as (ISEcp1-blaCTX-M-15-orf477), classical promoter-10 TACAAT and -35 TTGAA was found at the 3' region. The 3D structure of CTX-M-15 and ISEcp1 was generated and CTX-M-15-ISEcp1 (R299L) docking and mutation showed a reduction in hydrogen bonds. Co-occurrence of antibiotics and HMRGs (mer, sil, and ars) was found in 18, 14, and 8 isolates. PBRT analysis showed the presence of Inc. groups- B/O, F, I1, HI1, FIA, HI2, N, FIB, L/M. Molecular analysis of transconjugants showed the successful transfer of ARGs, MGEs, and HMRGs in the E. coli J53 AZ^R strain.

CONCLUSION

This study highlights the occurrence of ESBL producing bacteria in the aquatic environment of Kashmir India that can serve as a reservoir of ARGs. It also discussed the molecular mechanisms of MGEs which can help in containing the spread of antibiotic resistance.

First Report on the Phenotypic and Genotypic Susceptibility Profiles to Silver Nitrate in Bacterial Strains Isolated from Infected Leg Ulcers in Romanian Patients

Silver-ion-based antiseptics are widely used in treating chronic leg ulcers and, given the emergence of resistance to such compounds, the investigation of silver susceptibility and resistance profiles of pathogenic strains isolated from this type of wound is a topic of great interest. Therefore, in this study, 125 bacterial strains isolated from 103 patients with venous ulcers were investigated to elucidate their susceptibility to silver-nitrate solutions in planktonic and biofilm growth states, and the associated genetic determinants. The isolated strains, both in the planktonic and biofilm growth phases, showed high sensitivity to the standard concentration of 1/6000 silver-nitrate solution. It was noticed that even at concentrations lower than the clinical one (the first 2–3 binary dilutions in the case of planktonic cultures and the first 6–7 binary dilutions in the case of biofilms), the antiseptic solution proved to maintain its antibacterial activity. The phenotypic results were correlated with the genetic analysis, highlighting the presence of silver-resistance genes (sil operon) in only a few of the tested Staphylococcus sp. (especially in S. aureus) strains, Escherichia coli and Pseudomonas aeruginosa strains. These results demonstrate that despite its large use, this antiseptic remains a viable treatment alternative for the management of chronic leg wounds.

Unraveling the Underlying Heavy Metal Detoxification Mechanisms of Bacillus Species

The rise of anthropogenic activities has resulted in the increasing release of various contaminants into the environment, jeopardizing fragile ecosystems in the process. Heavy metals are one of the major pollutants that contribute to the escalating problem of environmental pollution, being primarily introduced in sensitive ecological habitats through industrial effluents, wastewater, as well as sewage of various industries. Where heavy metals like zinc, copper, manganese, and nickel serve key roles in regulating different biological processes in living systems, many heavy metals can be toxic even at low concentrations, such as mercury, arsenic, cadmium, chromium, and lead, and can accumulate in intricate food chains resulting in health concerns. Over the years, many physical and chemical methods of heavy metal removal have essentially been investigated, but their disadvantages like the generation of chemical waste, complex downstream processing, and the uneconomical cost of both methods, have rendered them inefficient,. Since then, microbial bioremediation, particularly the use of bacteria, has gained attention due to the feasibility and efficiency of using them in removing heavy metals from contaminated environments. Bacteria have several methods of processing heavy metals through general resistance mechanisms, biosorption, adsorption, and efflux mechanisms. Bacillus spp. are model Gram-positive bacteria that have been studied extensively for their biosorption abilities and molecular mechanisms that enable their survival as well as their ability to remove and detoxify heavy metals. This review aims to highlight the molecular methods of Bacillus spp. in removing various heavy metals ions from contaminated environments.

Clinically isolated bacteria resistance to silver-based wound dressings

OBJECTIVE

Silver has become a global treatment option with the US Food and Drug Administration providing marketing clearance for many silver-impregnated wound dressings and topical agents. However, the increased use of silver-based products across medical disciplines has raised questions concerning the development of acute silver resistance. In this study, the efficacy of previously identified silver-resistant clinical bacteria (Klebsiella pneumoniae and Enterobacter cloacae) against a variety of commercially available silver-based wound dressings was further investigated.

METHOD

To further explore the clinical significance of these isolates, multiple time-course and repeat-challenge assays were conducted with nine dressings using a panel of silver-resistant and silver-sensitive microorganisms. Silver-impregnated dressings were ranked by silver species, quantity of silver and overall efficacy.

RESULTS

Both silver-resistant strains were largely unaffected and exhibited phenotypic resistance even when exposed to the high silver concentrations found in commercially available wound dressings. In stark contrast, the majority of the dressings were able to maintain a high degree of efficacy over the course of 72 hours and during repeated bacterial challenges against silver-sensitive microorganisms.

CONCLUSION

Our findings provide additional evidence that clinically significant silver-resistance has emerged in the clinical setting. Such resistant microbes are capable of sustained silver resistance against a wide variety of silver adjuvants. These findings suggest that the further development and dissemination of these resistance mechanisms could significantly impact current practices in wound healing.

Effects of various wound dressings on microbial growth in perfused equine musculocutaneous flaps

OBJECTIVE

To compare the effect of multiple wound dressings on microbial growth in a perfused equine wound model.

SAMPLE

Abdominal musculocutaneous flaps from 16 equine cadavers.

PROCEDURES

8 full-thickness skin wound covered were created in each flap. Tissues were perfused with saline (0.9% NaCl) solution. Wounds were inoculated with methicillin-resistant Staphylococcus aureus (MRSA) or Pseudomonas aeruginosa (10⁶ CFUs), incubated, and covered with a dressing containing activated charcoal, boric acid, cadexomer iodine, calcium alginate, manuka honey, nanoparticle silver, or polyhexamethylene biguanide or with a control (nonadherent gauze) dressing. Muscle biopsy specimens were obtained at baseline (immediately prior to dressing application) and 6, 12, 18, and 24 hours later for mean bacterial load (MBL) determination. The MBLs at each subsequent time point were compared with that at baseline within dressing types, and MBLs at each time point were compared among dressing types.

RESULTS

MBLs in MRSA-inoculated wounds covered with cadexomer iodine dressings were significantly decreased from baseline at the 6- and 12-hour time points. For P aeruginosa-inoculated wounds, MBLs were significantly increased from baseline in all wounds at various times except for wounds with cadexomer iodine dressings. The MBLs of wounds with cadexomer iodine dressings were lower than all others, although not always significantly different from those for wounds with boric acid, manuka honey, nanoparticle silver, and polyhexamethylene biguanide dressings.

CONCLUSIONS AND CLINICAL RELEVANCE

In this nonviable perfused wound model, growth of MRSA and P aeruginosa was most effectively reduced or inhibited by cadexomer iodine dressings. These results and the effect of the dressings on wound healing should be confirmed with in vivo studies.

Risk and clinical impact of bacterial resistance/susceptibility to silver-based wound dressings: a systematic review

Objective:

To perform a systematic review of the literature on bacterial resistance, tolerance and susceptibility of silver within the context of wound therapy using silver-based dressings.

Methods:

A literature search was carried out using PubMed, Embase and Cochrane Library databases, the focus was whether results from microbiological experimental in vitro tests with reference strains and clinical wound isolates are reflected in clinical practice with regards to their ‘resistance’ profiles, comparable with those observed for antibiotics. The search results were allocated to six categories: resistance and resistance mechanism, in vitro tests with standard strains and wound isolates, prevalence and incidence, impact on clinical practice and impact on antibiotic therapy as well as reviews, expert opinions and consensus.

Results:

Based on all findings of the literature, it cannot be confirmed that a related clinical resistance to silver-ions in silver-based dressings has clinical impact, although endogenous and exogenous genetic resistance patterns have been described and intensively investigated. A translation of these genetic resistance-expression structures to phenotypic appearances, similar to those known for antibiotics, has not been demonstrated for silver in the literature.

Conclusion:

It can be concluded that there is no definitive evidence available and further studies should be conducted.

Silver Nanoparticles for the Therapy of Tuberculosis

Rapid emergence of aggressive, multidrug-resistant Mycobacteria strain represents the main cause of the current antimycobacterial-drug crisis and status of tuberculosis (TB) as a major global health problem. The relatively low-output of newly approved antibiotics contributes to the current orientation of research towards alternative antibacterial molecules such as advanced materials. Nanotechnology and nanoparticle research offers several exciting new-concepts and strategies which may prove to be valuable tools in improving the TB therapy. A new paradigm in antituberculous therapy using silver nanoparticles has the potential to overcome the medical limitations imposed in TB treatment by the drug resistance which is commonly reported for most of the current organic antibiotics. There is no doubt that AgNPs are promising future therapeutics for the medication of mycobacterial-induced diseases but the viability of this complementary strategy depends on overcoming several critical therapeutic issues as, poor delivery, variable intramacrophagic antimycobacterial efficiency, and residual toxicity. In this paper, we provide an overview of the pathology of mycobacterial-induced diseases, andhighlight the advantages and limitations of silver nanoparticles (AgNPs) in TB treatment.

Heritable nanosilver resistance in priority pathogen: a unique genetic adaptation and comparison with ionic silver and antibiotics

The past decade has seen the incorporation of antimicrobial nanosilver (NAg) into medical devices, and, increasingly, in everyday 'antibacterial' products. With the continued rise of antibiotic resistant bacteria, there are concerns that these priority pathogens will also develop resistance to the extensively commercialized nanoparticle antimicrobials. Herein, this work reports the emergence of stable resistance traits to NAg in the WHO-listed priority pathogen Staphylococcus aureus, which has previously been suggested to have no, or very low, capacity for silver resistance. With no native presence of genetically encoded silver defence mechanisms, the work showed that the bacterium is dependent on mutation of physiologically essential genes, including those involved in nucleotide synthesis and oxidative stress defence. While some mutations were uniquely associated with resistance to NAg, the study also found common mutations that could be protective against both NAg and ionic silver. This is consistent with the observation of NAg/ionic silver cross-resistance. These mutations were detected following withdrawal of the silver exposure, denoting heritable characteristics that allow for spread of the resistance traits even with discontinued silver use. Heritable silver resistance in priority pathogen cautions that these nanoparticle antimicrobials should only be used as needed, to preserve their efficacy for treating infections.

Consequences Of Long-Term Bacteria's Exposure To Silver Nanoformulations With Different PhysicoChemical Properties

Purpose

Resistance to antibiotics is a major problem of public health. One of the alternative therapies is silver – more and more popular because of nanotechnology development and new possibilities of usage. As a component of colloid, powder, cream, bandages, etc., nanosilver is often recommended to treat the multidrug-resistant pathogens and we can observe its overuse also outside of the clinic where different physicochemical forms of silver nanoformulations (e.g. size, shape, compounds, surface area) are introduced. In this research, we described the consequences of long-term bacteria exposure to silver nanoformulations with different physicochemical properties, including changes in genome and changes of bacterial sensitivity to silver nanoformulations and/or antibiotics. Moreover, the prevalence of exogenous resistance to silver among multidrug-resistant bacteria was determined.

Materials and Methods

Gram-negative and Gram-positive bacteria strains are described as sensitive and multidrug-resistant strains. The sensitivity of the tested bacterial strains to antibiotics was carried out with disc diffusion methods. The sensitivity of bacteria to silver nanoformulations and development of bacterial resistance to silver nanoformulations has been verified via determination of the minimal inhibitory concentrations. The presence of sil genes was verified via PCR reaction and DNA electrophoresis. The genomic and phenotypic changes have been verified via genome sequencing and bioinformatics analysis.

Results

Bacteria after long-term exposure to silver nanoformulations may change their sensitivity to silver forms and/or antibiotics, depending on the physicochemical properties of silver nanoformulations, resulting from phenotypic or genetic changes in the bacterial cell. Finally, adaptants and mutants may become more sensitive or resistant to some antibiotics than wild types.

Conclusion

Application of silver nanoformulations in the case of multiple resistance or multidrug-resistant bacterial infection can enhance or decrease their resistance to antibiotics. The usage of nanosilver in a clinic and outside of the clinic should be determined and should be under strong control. Moreover, each silver nanomaterial should be considered as a separate agent with a potential different mode of antibacterial action.

Non-antibiotic antimicrobial interventions and antimicrobial stewardship in wound care

Control of wound infection today relies largely on antibiotics, but the continual emergence of antibiotic-resistant microorganisms threatens a return to the pre-antibiotic era when physicians used antiseptics to prevent and manage infection. Some of those antiseptics are still used today, and others have become available. A diverse variety of non-antibiotic antimicrobial interventions are found on modern formularies. Unlike the mode of action of antibiotics, which affect specific cellular target sites of pathogens, many non-antibiotic antimicrobials affect multiple cellular target sites in a non-specific way. Although this reduces the likelihood of selecting for resistant strains of microorganisms, some have emerged and cross-resistance between antibiotics and antiseptics has been detected. With the prospect of a post-antibiotic era looming, ways to maintain and extend our antimicrobial armamentarium must be found. In this narrative review, current and emerging non-antibiotic antimicrobial strategies will be considered and the need for antimicrobial stewardship in wound care will be explained.

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

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 silver-resistance 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.

Appropriate use of dressings containing nanocrystalline silver to support antimicrobial stewardship in wounds

Antimicrobial resistance is an ever-increasing global concern, with the era of untreatable infection becoming a reality. Wound care is no exception, with increasing issues of antibiotic-resistant infections across different wound types and care settings. Antibiotic resistance and stewardship have been the priority for most strategic interventions so far; however, in wound care, alternative or supplementary strategies using antiseptics should be considered. Antiseptics such as silver can provide effective cidal activity across a broad range of wound pathogens, assuming they are used at the correct level for an appropriate duration. Evidence summarised in this manuscript suggests that effective antiseptics, such as nanocrystalline silver, have an increasing body of evidence in support of their use to minimise transmission of antibiotic-resistant organisms as part of institutional infection control procedures and, in addition, through appropriate early use and stewardship on local wound infections, in conjunction with local procedures, to minimise the need for systemic antibiotic therapy. Engagement, alignment, and collaboration between wound care professionals and wider related teams and governments on antimicrobial stewardship, and the potential role of antiseptics within this, will help to generate further evidence for such interventions in the fight against antimicrobial-resistant infections in wound care.

Heavy metal resistance in bacteria from animals

Resistance to metals and antimicrobials is a natural phenomenon that existed long before humans started to use these products for veterinary and human medicine. Bacteria carry diverse metal resistance genes, often harboured alongside antimicrobial resistance genes on plasmids or other mobile genetic elements. In this review we summarize the current knowledge about metal resistance genes in bacteria and we discuss their current use in the animal husbandry.

Bacterial Silver Resistance Gained by Cooperative Interspecies Redox Behavior

Silver has emerged as an important therapeutic option for wound infections in recent years due to its broad-spectrum antimicrobial activity. The silver cation (Ag⁺), but not the bulk metal (Ag⁰), is highly toxic for most microorganisms, although resistance due to genetic modification or horizontal gene transfer does occur. Pseudomonas aeruginosa, however, achieves silver resistance by producing the redox-active metabolite pyocyanin that reduces Ag⁺ to nontoxic Ag⁰ Pyocyanin also possesses broad-spectrum antimicrobial activity. Many microbial species reduce pyocyanin, which reduces molecular oxygen to antimicrobial hydrogen peroxide. In this study, it was hypothesized that both Ag⁺ and oxygen would act as competing terminal electron acceptors for pyocyanin, thus acting as a universal microbial protectant from Ag⁺ while avoiding hydrogen peroxide formation. Escherichia coli and Staphylococcus aureus efficiently reduced pyocyanin and generated hydrogen peroxide, while Ag⁺ markedly reduced the amount of hydrogen peroxide produced. Although unable to reduce directly Ag⁺ to Ag⁰ on their own, E. coli and S. aureus did so when pyocyanin was present, resulting in increased survival when exposed to Ag⁺ Coincubation experiments with either E. coli or S. aureus with P. aeruginosa demonstrated increased survival for those species to Ag⁺, but only if pyocyanin was present. These data demonstrate that microorganisms that display no intrinsic silver resistance may survive and proliferate under potentially toxic conditions, provided their environment contains a suitable redox-active metabolite-producing bacterium. Chronic wounds are often polymicrobial in nature, with pyocyanin-producing P. aeruginosa bacteria frequently being present; therefore, redox-based silver resistance may compromise treatment efforts.

Multidrug-Resistant CTX-M-(15, 9, 2)- and KPC-2-Producing Enterobacter hormaechei and Enterobacter asburiae Isolates Possessed a Set of Acquired Heavy Metal Tolerance Genes Including a Chromosomal sil Operon (for Acquired Silver Resistance)

Bacterial resistance to antibiotics is concern in healthcare-associated infections. On the other hand, bacterial tolerance to other antimicrobials, like heavy metals, has been neglected and underestimated in hospital pathogens. Silver has long been used as an antimicrobial agent and it seems to be an important indicator of heavy metal tolerance. To explore this perspective, we searched for the presence of acquired silver resistance genes (sil operon: silE, silS, silR, silC, silF, silB, silA, and silP) and acquired extended-spectrum cephalosporin and carbapenem resistance genes (bla_CTX−M and bla_KPC) in Enterobacter cloacae Complex (EcC) (n = 27) and Enterobacter aerogenes (n = 8) isolated from inpatients at a general hospital. Moreover, the genetic background of the silA (silver-efflux pump) and the presence of other acquired heavy metal tolerance genes, pcoD (copper-efflux pump), arsB (arsenite-efflux pump), terF (tellurite resistance protein), and merA (mercuric reductase) were also investigated. Outstandingly, 21/27 (78%) EcC isolates harbored silA gene located in the chromosome. Complete sil operon was found in 19/21 silA-positive EcC isolates. Interestingly, 8/20 (40%) E. hormaechei and 5/6 (83%) E. asburiae co-harbored silA/pcoD genes and bla_{CTX−M−(15,2,or9)} and/or bla_KPC−2 genes. Frequent occurrences of arsB, terF, and merA genes were detected, especially in silA/pcoD-positive, multidrug-resistant (MDR) and/or CTX-M-producing isolates. Our study showed co-presence of antibiotic and heavy metal tolerance genes in MDR EcC isolates. In our viewpoint, there are few studies regarding to bacterial heavy metal tolerance and we call attention for more investigations and discussion about this issue in different hospital pathogens.

Widespread and Indiscriminate Nanosilver Use: Genuine Potential for Microbial Resistance

In this era of increasing antibiotic resistance, the use of alternative antimicrobials such as silver has become more widespread. Superior antimicrobial activity has been provided through fabrication of silver nanoparticles or nanosilver (NAg), which imparts cytotoxic actions distinct from those of bulk silver. In the wake of the recent discoveries of bacterial resistance to NAg and its rising incorporation in medical and consumer goods such as wound dressings and dietary supplements, we argue that there is an urgent need to monitor the prevalence and spread of NAg microbial resistance. In this Perspective, we describe how the use of NAg in commercially available products facilitates prolonged microorganism exposure to bioavailable silver, which underpins the development of resistance. Furthermore, we advocate for a judicial approach toward NAg use in order to preserve its efficacy and to avoid environmental disruption.

Targeting biofilms of multidrug-resistant bacteria with silver oxynitrate

A topical antimicrobial, silver oxynitrate (Ag₇NO₁₁), has recently become available that exploits the antimicrobial activity of ionic silver but has enhanced activity because highly oxidised silver atoms are stabilised with oxygen in a unique chemical formulation. The objective of this study was to use a multifaceted approach to characterise the spectrum of antimicrobial and antibiofilm activity of a wound dressing coated with Ag₇NO₁₁ at a concentration of 0.4 mg Ag/cm². Physiochemical properties that influence efficacy were also evaluated, and Ag₇NO₁₁ was found to release a high level of Ag ions, including Ag²⁺ and Ag³⁺, without influencing the pH of the medium. Time-kill analysis demonstrated that a panel of multidrug-resistant pathogens isolated from wound specimens remained susceptible to Ag₇NO₁₁ over a period of 7 days, even with repeated inoculations of 1 × 10⁶ CFU/mL to the dressing. Furthermore, established 72-h-old biofilms of Pseudomonas aeruginosa, Staphylococcus aureus and two carbapenem-resistant Gram-negative bacteria (bla_NDM-1-positive Klebsiella pneumoniae and bla_VIM-2-positive P. aeruginosa) were disrupted and eradicated by Ag₇NO₁₁ in vitro. Ag₇NO₁₁ is a proprietary compound that exploits novel Ag chemistry and can be considered a new class of topical antimicrobial agent. Biocompatibility testing has concluded Ag₇NO₁₁ to be non-toxic for cytotoxicity, acute systemic toxicity, irritation and sensitisation.

Comparison of antibacterial effects among three foams used with negative pressure wound therapy in an ex vivo equine perfused wound model

OBJECTIVE To compare antibacterial effects among 3 types of foam used with negative-pressure wound therapy (NPWT) in an ex vivo equine perfused wound model. SAMPLES Abdominal musculocutaneous flaps from 6 equine cadavers. PROCEDURES Each musculocutaneous flap was continuously perfused with saline (0.9% NaCl) solution. Four 5-cm circular wounds were created in each flap and contaminated with 10⁶ CFUs of both Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA). After a 1-hour incubation period, 1 of 4 treatments (NPWT with silver-impregnated polyurethane foam [NPWT-AgPU], polyurethane foam [NPWT-PU], or polyvinyl alcohol foam [NPWT-PVA] or a nonadherent dressing containing polyhexamethylene biguanide without NPWT [control]) was randomly applied to each wound. An 8-mm punch biopsy specimen was obtained from each wound immediately before and at 6, 12, 18, and 24 hours after treatment application to determine the bacterial load for both P aeruginosa and MRSA. RESULTS The bacterial load of P aeruginosa for the NPWT-PVA treatment was significantly lower than that for the other 3 treatments at each sampling time after application, whereas the bacterial load for the NPWT-AgPU treatment was significantly lower than that for the NPWT-PU and control treatments at 12 hours after application. The bacterial load of MRSA for the NPWT-PVA treatment was significantly lower than that for the other 3 treatments at each sampling time after application. CONCLUSIONS AND CLINICAL RELEVANCE Results indicated that wounds treated with NPWT-PVA had the greatest decrease in bacterial load; however, the effect of that treatment on wound healing needs to be assessed in vivo.

Characterization of surface antigen protein 1 (SurA1) from Acinetobacter baumannii and its role in virulence and fitness

Acinetobacter baumannii is a Gram-negative bacillus that causes nosocomial infections, such as bacteremia, pneumonia, and meningitis and urinary tract and wound infections. In the present study, the surface antigen protein 1 (SurA1) gene of A. baumannii strain CCGGD201101 was identified, cloned and expressed, and then its roles in fitness and virulence were investigated. Virulence was observed in the human lung cancer cell lines A549 and HEp-2 at one week after treatment with recombinant SurA1. One isogenic SurA1 knock-out strain, GR0015, which was derived from the A. baumannii strain CCGGD201101 isolated from diseased chicks in a previous study, highlighted the effect of SurA1 on fitness and growth. Its growth rate in LB broth and killing activity in human sera were significantly decreased compared with strain CCGGD201101. In the Galleria mellonella insect model, the isogenic SurA1 knock-out strain exhibited a lower survival rate and decreased dissemination. These results suggest that SurA1 plays an important role in the fitness and virulence of A. baumannii.

Specific Gene Loci of Clinical Pseudomonas putida Isolates

Pseudomonas putida are ubiquitous inhabitants of soils and clinical isolates of this species have been seldom described. Clinical isolates show significant variability in their ability to cause damage to hosts because some of them are able to modulate the host’s immune response. In the current study, comparisons between the genomes of different clinical and environmental strains of P. putida were done to identify genetic clusters shared by clinical isolates that are not present in environmental isolates. We show that in clinical strains specific genes are mostly present on transposons, and that this set of genes exhibit high identity with genes found in pathogens and opportunistic pathogens. The set of genes prevalent in P. putida clinical isolates, and absent in environmental isolates, are related with survival under oxidative stress conditions, resistance against biocides, amino acid metabolism and toxin/antitoxin (TA) systems. This set of functions have influence in colonization and survival within human tissues, since they avoid host immune response or enhance stress resistance. An in depth bioinformatic analysis was also carried out to identify genetic clusters that are exclusive to each of the clinical isolates and that correlate with phenotypical differences between them, a secretion system type III-like was found in one of these clinical strains, a determinant of pathogenicity in Gram-negative bacteria.

Changes in soil bacterial communities and diversity in response to long-term silver exposure

Silver-induced selective pressure is becoming increasingly important due to the growing use of silver (Ag) as an antimicrobial agent in biomedical and commercial products. With demonstrated links between environmental resistomes and clinical pathogens, it is important to identify microbial profiles related to silver tolerance/resistance. We investigated the effects of ionic Ag stress on soil bacterial communities and identified resistant/persistent bacterial populations. Silver treatments of 50-400 mg Ag kg(-1) soil were established in five soils. Chemical lability measurements using diffusive gradients in thin-film devices confirmed that significant (albeit decreasing) labile Ag concentrations were present throughout the 9-month incubation period. Synchrotron X-ray absorption near edge structure spectroscopy demonstrated that this decreasing lability was due to changes in the Ag speciation to less soluble forms such as Ag(0) and Ag2S. Real-time PCR and Illumina MiSeq screening of 16S rRNA bacterial genes showed β-diversity changes, increasing α-diversity in response to Ag pressure, and immediate and significant reductions in 16S rRNA gene counts with varying degrees of recovery. These effects were more strongly influenced by exposure time than by Ag dose at these rates. Ag-selected dominant OTUs principally resided in known persister taxa (mainly Gram positive), including metal-tolerant bacteria and slow-growing Mycobacteria.

Unprecedented Silver Resistance in Clinically Isolated Enterobacteriaceae: Major Implications for Burn and Wound Management

Increased utilization of inorganic silver as an adjunctive to many medical devices has raised concerns of emergent silver resistance in clinical bacteria. Although the molecular basis for silver resistance has been previously characterized, to date, significant phenotypic expression of these genes in clinical settings is yet to be observed. Here, we identified the first strains of clinical bacteria expressing silver resistance at a level that could significantly impact wound care and the use of silver-based dressings. Screening of 859 clinical isolates confirmed 31 harbored at least 1 silver resistance gene. Despite the presence of these genes, MIC testing revealed most of the bacteria displayed little or no increase in resistance to ionic silver (200 to 300 μM Ag(+)). However, 2 isolates (Klebsiella pneumonia and Enterobacter cloacae) were capable of robust growth at exceedingly high silver concentrations, with MIC values reaching 5,500 μM Ag(+). DNA sequencing of these two strains revealed the presence of genes homologous to known genetic determinants of heavy metal resistance. Darkening of the bacteria's pigment was observed after exposure to high silver concentrations. Scanning electron microscopy images showed the presence of silver nanoparticles embedded in the extracellular polymeric substance of both isolates. This finding suggested that the isolates may neutralize ionic silver via reduction to elemental silver. Antimicrobial testing revealed both organisms to be completely resistant to many commercially available silver-impregnated burn and wound dressings. Taken together, these findings provide the first evidence of clinical bacteria capable of expressing silver resistance at levels that could significantly impact wound management.

Impact of polymethylmethacrylate additives on methicillin-resistant Staphylococcus pseudintermedius biofilm formation in vitro

OBJECTIVE

To evaluate the impact of gentamicin, silver, or both additives in polymethylmethacrylate (PMMA) beads on methicillin-resistant Staphylococcus pseudintermedius (MRSP) biofilm formation in vitro.

SAMPLE

4 preparations of PMMA beads (formed with no additive [control], gentamicin, silver, and gentamicin and silver).

PROCEDURES

Beads from each group were exposed to 10 MRSP isolates known to be strong biofilm formers. Following incubation, the beads were rinsed to remove planktonic bacteria, then sonicated to dislodge biofilm-associated bacteria. Resulting suspensions were serially diluted, plated on blood agar, and incubated overnight; CFUs were counted. Variance of mean CFU counts following log10 transformation was analyzed among PMMA groups.

RESULTS

None of the PMMA additives tested completely inhibited MRSP biofilm formation. There was a significant effect of gentamicin and gentamicin plus silver on this variable, compared with controls, but not of silver alone. There was no difference between gentamicin and gentamicin plus silver. When only isolates not susceptible to gentamicin were evaluated, there were no significant differences among PMMA additive groups. Within gentamicin-susceptible isolates, there was an impact of gentamicin and gentamicin plus silver, but no impact of silver alone and no difference between gentamicin and gentamicin plus silver.

CONCLUSIONS AND CLINICAL RELEVANCE

Gentamicin-impregnated PMMA was effective at reducing biofilm formation of gentamicin-susceptible MRSP isolates but had no effect on isolates not susceptible to gentamicin. Silver-impregnated PMMA had no effect on MRSP biofilm formation. Results suggested that gentamicin-impregnated PMMA may not be effective in vivo against MRSP isolates not susceptible to gentamicin. Antibacterial efficacy of silver should not be assumed without proper testing of the target bacteria and specific silver compound.

Metal tolerance in emerging clinically relevant multidrug-resistant Salmonella enterica serotype 4,[5],12:i:- clones circulating in Europe

The occurrence of acquired metal tolerance genes in emerging MDR Salmonella enterica serotype 4,[5],12:i:- clones was assessed and their associated platforms and tolerance phenotype were characterised. Salmonella 4,[5],12:i:- from different sources belonging to European, Spanish and Southern European clones were studied. Screening for copper (pcoA-pcoD/tcrB), silver/copper (silA-silE), mercury (merA), arsenic (arsB) and tellurite (terF) tolerance genes was performed by PCR/sequencing. CuSO(4)/AgNO(3) MICs were determined in aerobic/anaerobic atmospheres by agar dilution. Conjugation assays, genomic location and plasmid analysis were performed by standard procedures. Most isolates from European (98%) and Spanish (74%) clones carried silA-silE, contrasting with the Southern European clone (26%). merA/62% (European and Spanish clones) and pcoA-pcoD/50% (European clone) were also detected. merA±pco+sil were chromosomally located in the European clone, whereas in Spanish and Southern European clones sil±merA were within plasmids, both with antibiotic resistance genes. The pcoA-pcoD/silA-silE(+) isolates showed higher MICCuSO(4) in anaerobiosis than those without these genes (MIC(50)=24-28 vs. 2 mM). Different MICAgNO(3) of silA-silE(+) (MIC(50)=0.25 mM) and silA-silE(-)(MIC(50)=0.16 mM) isolates were observed in both atmospheres, with an MIC increment after prior exposure to silver (>3 vs. 0.08-0.125 mM) in aerobiosis. A high frequency of copper and silver tolerance, particularly among the two major Salmonella 4,[5],12:i:- MDR clones (European/Spanish) circulating in Europe and causing human infections, might facilitate adaptation/expansion of these strains in metal-contaminated environments, particularly copper in anaerobiosis. Furthermore, metal toxic concentrations in food-animal environments can contribute to persistence of genetic platforms carrying metal/antibiotic resistance genes in this foodborne zoonotic pathogen.

Bacterial antimicrobial metal ion resistance

Metals such as mercury, arsenic, copper and silver have been used in various forms as antimicrobials for thousands of years with until recently, little understanding of their mode of action. The discovery of antibiotics and new organic antimicrobial compounds during the twentieth century saw a general decline in the clinical use of antimicrobial metal compounds, with the exception of the rediscovery of the use of silver for burns treatments and niche uses for other metal compounds. Antibiotics and new antimicrobials were regarded as being safer for the patient and more effective than the metal-based compounds they supplanted. Bacterial metal ion resistances were first discovered in the second half of the twentieth century. The detailed mechanisms of resistance have now been characterized in a wide range of bacteria. As the use of antimicrobial metals is limited, it is legitimate to ask: are antimicrobial metal resistances in pathogenic and commensal bacteria important now? This review details the new, rediscovered and 'never went away' uses of antimicrobial metals; examines the prevalence and linkage of antimicrobial metal resistance genes to other antimicrobial resistance genes; and examines the evidence for horizontal transfer of these genes between bacteria. Finally, we discuss the possible implications of the widespread dissemination of these resistances on re-emergent uses of antimicrobial metals and how this could impact upon the antibiotic resistance problem.

Persistence of nosocomial bacteria on 2 biocidal fabrics based on silver under conditions of high relative humidity

BACKGROUND

The survival of pathogenic microorganism on fabrics in the health care environment has a important role in nosocomial infections. The use of biocidal fabrics and surfaces could reduce the prevalence of the microorganisms in the hospital environment.

METHODS

In this study, the persistence of nosocomial bacteria on 2 fabrics containing biocidal fibers (BF) in the long term following desiccation and subsequent storage was examined at 40% and 90% relative humidity (RH).

RESULTS

Very few strains survived more than 7 days at 40% RH on fabrics containing 67% BF, and only strains of Acinetobacter baumanii and Pseudomonas aeruginosa survived on fabric containing 100% BF. None of the strains tested survived 14 days on the 2 fabrics, 67% or 100% BF, under these environmental conditions. In contrast, at higher RH (∼90%), most of the strains tested showed prolonged survival on both fabrics, and all strains of Klebsiella pneumoniae, Enterobacter aerogenes, and A baumannii survived for more than 14 days; however, in a Petri dish, most of the microorganisms tested showed a higher survival even at 28 days. The gram-positive cocci and A baumannii were the most persistent bacteria on the Petri dish.

CONCLUSIONS

This study emphasizes the effect of RH on the survival of nosocomial bacteria on 2 commercially available fabrics containing biocide. Evidence of the clinical efficacy of these BF-containing fabrics is lacking.

A preliminary study of silver sodium zirconium phosphate polyurethane foam wound dressing on wounds of the distal aspect of the forelimb in horses

OBJECTIVE

To determine if application of silver sodium zirconium phosphate polyurethane semi-occlusive foam (SPF) dressing would improve measures of wound healing and decrease bacterial contamination compared with a non-adherent, absorbent dressing applied to wounds created on the distal aspect of the equine limb.

STUDY DESIGN

Controlled randomized experimental study.

ANIMALS

Adult Quarter Horse and Thoroughbred horses (n = 5).

METHODS

One 6.25 cm(2) wound was created on the dorsomedial aspect of the proximal metacarpus on each forelimb. A SPF dressing was applied to 1 randomly assigned limb as a treatment and a non-adherent, absorbent dressing was applied to the opposite limb as control. Bandages were changed every 3 days for 60 days. Granulation tissue was scored every 3 days, wound area measured every 6 days, and wound bed was cultured every 12 days.

RESULTS

SPF-treatment wounds had significantly decreased wound area and decreased granulation tissue scores when evaluated <30 days and over the 60 day study, although complete wound healing times were not significantly different. Bacteria were cultured from all wounds at varying times throughout the study.

CONCLUSIONS

The SPF wound dressing improved some measures of wound healing compared with the control dressing, most significantly during the first 30 days. This suggests that the SPF wound dressing may be useful in the early management of wounds on the equine lower limb. Further studies using the SPF dressing are needed to characterize the temporal and cellular effects on wound healing and evaluate this dressing in a clinical environment.

Pyocyanin production by Pseudomonas aeruginosa confers resistance to ionic silver

Silver in its ionic form (Ag+), but not the bulk metal (Ag0), is toxic to microbial life forms and has been used for many years in the treatment of wound infections. The prevalence of bacterial resistance to silver is considered low due to the nonspecific nature of its toxicity. However, the recent increased use of silver as an antimicrobial agent for medical, consumer, and industrial products has raised concern that widespread silver resistance may emerge. Pseudomonas aeruginosa is a common pathogen that produces pyocyanin, a redox toxin and a reductant for molecular oxygen and ferric (Fe3+) ions. The objective of this study was to determine whether pyocyanin reduces Ag+ to Ag0, which may contribute to silver resistance due to lower bioavailability of the cation. Using surface plasmon resonance spectroscopy and scanning electron microscopy, pyocyanin was confirmed to be a reductant for Ag+, forming Ag0 nanoparticles and reducing the bioavailability of free Ag+ by >95% within minutes. Similarly, a pyocyanin-producing strain of P. aeruginosa (PA14) reduced Ag+ but not a pyocyanin-deficient (ΔphzM) strain of the bacterium. Challenge of each strain with Ag+ (as AgNO3) gave MICs of 20 and 5 μg/ml for the PA14 and ΔphzM strains, respectively. Removal of pyocyanin from the medium strain PA14 was grown in or its addition to the medium that ΔphzM mutant was grown in gave MICs of 5 and 20 μg/ml, respectively. Clinical isolates demonstrated similar pyocyanin-dependent resistance to Ag+. We conclude that pseudomonal silver resistance exists independently of previously recognized intracellular mechanisms and may be more prevalent than previously considered.

Antibacterial activity of silver nanoparticles: sensitivity of different Salmonella serovars

Salmonella spp. is one of the main causes of foodborne illnesses in humans worldwide. Consequently, great interest exists in reducing its impact on human health by lowering its prevalence in the food chain. Antimicrobial formulations in the form of nanoparticles exert bactericidal action due to their enhanced reactivity resultant from their high surface/volume ratio. Silver nanoparticles (AgNPs) are known to be highly toxic to Gram-negative and Gram-positive microorganisms, including multidrug resistant bacteria. However, few data concerning their success against different Salmonella serovars are available. Aims of the present study were to test the antimicrobial effectiveness of AgNPs, against Salmonella Enteritidis, Hadar, and Senftenberg, and to investigate the causes of their different survival abilities from a molecular point of view. Results showed an immediate, time-limited and serovar-dependent reduction of bacterial viability. In the case of S. Senftenberg, the reduction in numbers was observed for up to 4 h of incubation in the presence of 200 mg/l of AgNPs; on the contrary, S. Enteritidis and S. Hadar resulted to be inhibited for up to 48 h. Reverse transcription and polymerase chain reaction experiments demonstrated the constitutive expression of the plasmidic silver resistance determinant (SilB) by S. Senftenberg, thus suggesting the importance of a cautious use of AgNPs.

Induced adaptation of Bacillus sp. to antimicrobial nanosilver

The natural ability of Bacillus sp. to adapt to nanosilver cytotoxicity upon prolonged exposure is reported for the first time. The combined adaptive effects of nanosilver resistance and enhanced growth are induced under various intensities of nanosilver-stimulated cellular oxidative stress, ranging from only minimal cellular redox imbalance to the lethal levels of cellular ROS stimulation. An important implication of the present work is that such adaptive effects lead to the ultimate domination of nanosilver-resistant Bacillus sp. in the microbiota, to which nanosilver cytotoxicity is continuously applied.

Nanosilver: application and novel aspects of toxicology

Nanomaterials are a challenge to toxicology. The high diversity of novel materials and products will require extensive expertize for evaluation and regulatory efforts. Nanomaterials are of substantial scientific and economic potential. Here, we will focus on nanosilver, a material not only with medical applications, but a rapidly increasing use in surprisingly many products. Consequently, toxicological evaluation has to cover an increasing range of complex topics. The toxicology of nanosilver is advancing rapidly; regulatory efforts by Federal Drug Agency and European Environment Protection Agencies are substantial. Current toxicological data, ranging from in vitro studies with cell lines to rodent experiments and ecological evaluation, are numerous, and many groups are providing continuously new data. However, standard classification based on nanosize only is neglecting nanoshape, which adds another level of complexity to the analysis of biological effects. A surprising neglect in nanosilver toxicology so far is the analysis of effects of nanosilver on amyloidosis. Amyloid diseases are widespread in humans and a severe health hazard. The known potential of silver to stimulate amyloidosis in rodents will require a timely and balanced evaluation of nanosilvers.

Silver as an antimicrobial: facts and gaps in knowledge

Silver has been used for centuries. Today, silver and silver nanoparticles (AgNPs) are used in a wide range of healthcare, food industry, domiciliary applications, and are commonly found in hard surface materials and textiles. Such an extensive use raises questions about its safety, environmental toxicity and the risks associated with microbial resistance and cross-resistance. If the mechanisms of antimicrobial action of ionic silver (Ag+) have been studied, there is little understanding of AgNPs interactions with microorganisms. There have been excellent reviews on the bacterial resistance mechanisms to silver, but there is a paucity of information on resistance to AgNPs. Silver toxicity and accumulation in the environment has been studied and there is a better understanding of silver concentration and species in different environmental compartments. However, owing to the increased applications of silver and AgNPs, questions remain about the presence and consequences of AgNPs in the environment. This review provides an historical perspective of silver usage, an overview of applications, and combined information of microbial resistance and toxicity. Owing the evidence provided in this review, a call for a better understanding and control of silver usage, and for tighter regulations of silver and AgNPs usage is proposed.

Subtractive hybridization yields a silver resistance determinant unique to nosocomial pathogens in the Enterobacter cloacae complex

The heterogeneity and the increasing clinical importance of the Enterobacter cloacae complex have often been discussed. However, little is known about molecular factors causing pathogenicity within this nomenspecies. Here, we analyzed the genetic differences between an avirulent plant isolate and a pathogenic strain causing an outbreak with septicemia in three patients. We identified an IncHI-2 plasmid as a major difference between these two strains. Besides resistance to several antibiotics, this plasmid encoded a silver resistance determinant. We further showed that this sil determinant was present not only in the analyzed outbreak strain but also in the vast majority of clinical isolates of the E. cloacae complex, predominantly in (sub)species that frequently cause nosocomial infections. The identified sil determinant was highly conserved within the E. cloacae complex and mediated resistance to up to 600 μM silver nitrate. As silver is often used as a disinfectant and treatment for burn wounds, we present here an important fitness factor within the clinically most prevalent subspecies of the E. cloacae complex. This provides a possible explanation for their unequal involvement in nosocomial and especially burn wound infections.

Copper and silver ion implantation of aluminium oxide-blasted titanium surfaces: proliferative response of osteoblasts and antibacterial effects

Implant infection still represents a major clinical problem in orthopedic surgery. We therefore tested the in vitro biocompatibility and antibacterial effects of copper (Cu)- and silver (Ag)-ion implantation. Discs of a commonly used titanium alloy (Ti6AlV4) with an aluminium oxide-blasted surface were treated by Cu- or Ag-ion implantation with different dosage regimen (ranging from 1e15-17 ions cm(-2) at energies of 2-20 keV). The samples were seeded with primary human osteoblasts and cell attachment and proliferation was analyzed by an MTT-assay. In comparison to the reference titanium alloy there was no difference in the number of attached viable cells after two days. After seven days the number of viable cells was increased for Cu with 1e17 ions cm(-2) at 2 and 5 keV, and for Ag with 1e16 ions cm(-2) at 5 keV while it was reduced for the highest amount of Ag deposition (1e17 ions cm(-2) at 20 keV). Antibacterial effects on S.aureus and E.coli were marginal for the studied dosages of Cu but clearly present for Ag with 1e16 ions cm(-2) at 2 and 5 keV and 1e17 ions cm(-2) at 20 keV. These results indicate that Ag-ion implantation may be a promising methodological approach for antibacterial functionalization of titanium implants.

The visualisation and speed of kill of wound isolates on a silver alginate dressing

In chronic wound management, alginate dressings are used to absorb exudate and reduce the microbial burden. Silver alginate offers the added benefit of an additional antimicrobial pressure on contaminating microorganisms. This present study compares the antimicrobial activity of a RESTORE silver alginate dressing with a silver-free control dressing using a combination of in vitro culture and imaging techniques. The wound pathogens examined included Candida albicans, Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, β-haemolytic Streptococcus, and strictly anaerobic bacteria. The antimicrobial efficacy of the dressings was assessed using log(10) reduction and 13-day corrected zone of inhibition (CZOI) time-course assays. Confocal laser scanning microscopy (CLSM) was used to visualise the relative proportions of live/dead microorganisms sequestered into the dressings over 24 hours and estimate the comparative speed of kill. The RESTORE silver alginate dressing showed significantly greater log(10) reductions and CZOIs for all microorganisms compared with the control, indicating the antimicrobial effect of ionic silver. Antimicrobial activity was evident against all test organisms for up to 5 days and, in some cases, up to 12 days following an on-going microbial challenge. Imaging bacteria sequestered in the silver-free dressing showed that each microbial species aggregated in the dressing and remained viable for more than 20 hours. Growth was not observed inside of the dressing, indicating a possible microbiostatic effect of the alginate fibres. In comparison, organisms in the RESTORE silver alginate dressing were seen to lose viability at a considerably greater rate. After 16 hours of contact with the RESTORE silver alginate dressing, >90% of cells of all bacteria and yeast were no longer viable. In conclusion, collectively, the data highlights the rapid speed of kill and antimicrobial suitability of this RESTORE silver alginate dressing on wound isolates and highlights its overwhelming ability to manage a microbial wound bioburden in the management of infected wounds.

Identification of Enterococcus faecalis bacteria resistant to heavy metals and antibiotics in surface waters of the Mololoa River in Tepic, Nayarit, Mexico

Heavy metal and antibiotic resistance have been shown to have a strong correlation in nature, and their inter-relation is an important subject of study. We report an analysis of surface waters of the Mololoa River in the municipality of Tepic, state of Nayarit, Mexico. This river has two distinctive sources of contamination: sewage waters and trash confinements. Our findings demonstrate a correlation between the river flow pattern and resistance to heavy metals or to heavy metals and antibiotics in isolated bacteria of the genus Enterococcus, specifically Enterococcus faecalis. The Mololoa River provides a model to study the relationship between water flow and generation of biodiversity, and more importantly, it constitutes a model for studying genetic diversity of bacteria affecting human health.

The effect of silver impregnation of surgical scrub suits on surface bacterial contamination

Silver-impregnated fabrics are widely used for their antibacterial and antifungal effects, including for clinical clothing such as surgical scrub suits (scrubs). This study investigated whether silver impregnation reduces surface bacterial contamination of surgical scrubs during use in a veterinary hospital. Using agar contact plates, abdominal and lumbar areas of silver-impregnated nylon or polyester/cotton scrubs were sampled for surface bacterial contamination before (0 h) and after 4 and 8 h of use. The number of bacterial colonies on each contact plate was counted after 24 and 48 h incubation at 37 °C. Standard basic descriptive statistics and mixed-effects linear regression were used to investigate the association of possible predictors of the level of bacterial contamination of the scrubs with surface bacterial counts.

Silver-impregnated scrubs had significantly lowered bacterial colony counts (BCC) at 0 h compared with polyester/cotton scrubs. However, after 4 and 8 h of wear, silver impregnation had no effect on BCC. Scrub tops with higher BCC at 0 h had significantly higher BCC at 4 and 8 h, suggesting that contamination present at 0 h persisted during wear. Sampling from the lumbar area was associated with lower BCC at all three time points. Other factors (contamination of the scrub top with a medication/drug, restraint of patients, working in the anaesthesia recovery area) also affected BCC at some time points. Silver impregnation appeared to be ineffective in reducing bacterial contamination of scrubs during use in a veterinary hospital.