Drug resistance in relation to use of silver sulphadiazine cream in a burns unit

Resistance of Bacteria to Biocides

Biocides and formulated biocides are used worldwide for an increasing number of applications despite tightening regulations in Europe and in the United States. One concern is that such intense usage of biocides could lead to increased bacterial resistance to a product and cross-resistance to unrelated antimicrobials including chemotherapeutic antibiotics. Evidence to justify such a concern comes mostly from the use of health care-relevant bacterial isolates, although the number of studies of the resistance characteristics of veterinary isolates to biocides have increased the past few years. One problem remains the definition of "resistance" and how to measure resistance to a biocide. This has yet to be addressed globally, although the measurement of resistance is becoming more pressing, with regulators both in Europe and in the United States demanding that manufacturers provide evidence that their biocidal products will not impact on bacterial resistance. Alongside in vitro evidence of potential antimicrobial cross-resistance following biocide exposure, our understanding of the mechanisms of bacterial resistance and, more recently, our understanding of the effect of biocides to induce a mechanism(s) of resistance in bacteria has improved. This article aims to provide an understanding of the development of antimicrobial resistance in bacteria following a biocide exposure. The sections provide evidence of the occurrence of bacterial resistance and its mechanisms of action and debate how to measure bacterial resistance to biocides. Examples pertinent to the veterinary field are used where appropriate.

Metal Resistance and Its Association With Antibiotic Resistance

Antibiotic resistance is recognised as a major global threat to public health by the World Health Organization. Currently, several hundred thousand deaths yearly can be attributed to infections with antibiotic-resistant bacteria. The major driver for the development of antibiotic resistance is considered to be the use, misuse and overuse of antibiotics in humans and animals. Nonantibiotic compounds, such as antibacterial biocides and metals, may also contribute to the promotion of antibiotic resistance through co-selection. This may occur when resistance genes to both antibiotics and metals/biocides are co-located together in the same cell (co-resistance), or a single resistance mechanism (e.g. an efflux pump) confers resistance to both antibiotics and biocides/metals (cross-resistance), leading to co-selection of bacterial strains, or mobile genetic elements that they carry. Here, we review antimicrobial metal resistance in the context of the antibiotic resistance problem, discuss co-selection, and highlight critical knowledge gaps in our understanding.

Burn Wound Sepsis

Wound sepsis remains perhaps the most feared sequela in the patient who has suffered major burn injuries and leads to overwhelming mortality among patients with extensive burn wounds. The presence of large areas of devitalized, necrotic tissue, coupled with the profound immunosuppression that usually follows major injury, sets the stage for rapid microbial proliferation in the wound; when microbes invade subjacent, previously vi able tissues, invasive burn wound sepsis is defined. Top ical antimicrobial drugs probably have only a limited effect in preventing wound sepsis, and organisms now frequently emerge that are resistant to the commonly used topical agents. Salient factors in the diagnosis and treatment of invasive wound sepsis are discussed in this review. Prevention of wound sepsis, however, is one of the primary objectives of current burn care. Early burn wound excision and immediate wound closure with autograft or a suitable biologic dressing has emerged as the best means for prevention of generalized wound sepsis.

Is reduced susceptibility to disinfectants and antiseptics a risk in healthcare settings? A point/counterpoint review

BACKGROUND

Given the breadth and depth of antiseptic use, it is surprising how few large-scale studies have been undertaken into the consequences of their use, particularly in clinical practice. Depending on your point of view, this may either reflect an assurance that reduced susceptibility to antiseptics, and notably whether this confers cross-resistance to systemically administered antimicrobial agents, is not an issue of concern, or relative ignorance about the potential threat.

AIM

This point/counterpoint review offers a differentiated perspective and possible answers to the question, 'Should we be worried about reduced susceptibility to disinfectants and antiseptics in healthcare settings?'.

METHODS

This topic was the subject of a debate by MHW (point) and SH (counterpoint) during the SHEA Spring Conference 2013: Advancing healthcare epidemiology and the role of the environment, held in Atlanta, GA, USA on 4(th) May 2013. This review is a general representation of the main themes presented during the debate, rather than a systematic review of the literature.

FINDINGS

There are examples of reduced susceptibility to antiseptics in clinical practice; however, to date, there is no strong evidence that reduced susceptibility to antiseptics is a major clinical problem. Given the growing number of potential indications for use of biocidal active ingredients, the potential for emergence of reduced susceptibility remains a concern.

CONCLUSIONS

Changes in the clinical use of antiseptics should be matched with surveillance studies to understand whether there are unintended microbiological or clinical consequences, including the selection of bacterial strains that can survive exposure to antiseptics.

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.

Effects of three different topical antibacterial dressings on Acinetobacter baumannii-contaminated full-thickness burns in rats

In this animal study, three topical antibacterial dressings, Acticoat, chlorhexidine acetate 0.5% and silver sulfadiazine 1%, were compared in the treatment of Acinetobacter baumannii contamination of burns. All treatments were effective and prevented the organism invading the muscle and causing systemic infection, so there were significant differences between the results of the treatment groups and the control group. Mean eschar concentrations did not differ significantly between the silver sulfadiazine and chlorhexidine acetate groups, but there were significant differences between these and the Acticoat group, indicating that Acticoat eliminated A. baumannii from the tissues more effectively.

Bacterial resistance to biocides in the healthcare environment: should it be of genuine concern?

The emergence of bacterial resistance following exposure in healthcare facilities has been a recurrent topic of interest over the last 10 years. The overwhelming and increasing body of evidence from studies in vitro showed that bacteria have an immense capacity to respond to chemical stress brought upon by biocides. Empirically two major types of mechanisms have been described: intrinsic and acquired. However, the increasing documented response from bacteria exposed to biocide in conditions close to those found in practice suggests that intrinsic resistance does not adequately describe bacterial survival mechanisms, and that other terms such as biofilm resistance and environmental resistance would be therefore more appropriate. In addition, such terms are more relevant when describing in-situ conditions. The lack of evidence of bacterial resistance in practice and the inability to correlate emerging bacterial resistance from in-vitro experiments with practical situations is a major drawback when attempting to ascertain whether emerging bacterial resistance in healthcare facilities is of genuine concern. Microbial resistance to high or in-use concentration of biocides has been described in practice, although it remains uncommon. The efficacy of biocides in eliminating bacterial contaminants within healthcare facilities has to be questioned with the widespread and increasing use of products containing low concentrations of biocide or possessing low bactericidal activity, as is the selection of less susceptible bacteria following such exposure.

Antimicrobial biocides in the healthcare environment: efficacy, usage, policies, and perceived problems

Biocides are heavily used in the healthcare environment, mainly for the disinfection of surfaces, water, equipment, and antisepsis, but also for the sterilization of medical devices and preservation of pharmaceutical and medicinal products. The number of biocidal products for such usage continuously increases along with the number of applications, although some are prone to controversies. There are hundreds of products containing low concentrations of biocides, including various fabrics such as linen, curtains, mattresses, and mops that claim to help control infection, although evidence has not been evaluated in practice. Concurrently, the incidence of hospital-associated infections (HAIs) caused notably by bacterial pathogens such as methicillin-resistant Staphylococcus aureus (MRSA) remains high. The intensive use of biocides is the subject of current debate. Some professionals would like to see an increase in their use throughout hospitals, whereas others call for a restriction in their usage to where the risk of pathogen transmission to patients is high. In addition, the possible linkage between biocide and antibiotic resistance in bacteria and the role of biocides in the emergence of such resistance has provided more controversies in their extensive and indiscriminate usage. When used appropriately, biocidal products have a very important role to play in the control of HAIs. This paper discusses the benefits and problems associated with the use of biocides in the healthcare environment and provides a constructive view on their overall usefulness in the hospital setting.

Generally overlooked fundamentals of bacterial genetics and ecology

Several important aspects of the antimicrobial resistance problem have not been treated extensively in previous monographs on this subject. This section very briefly updates information on these topics and suggests how this information is of value in assessing the contributions of human and agricultural use of antimicrobial agents on the problem of increasing antimicrobial resistance. The overall themes are (1) that propagation of resistance is an ecological problem, and thus (2) that ameliorating this problem requires recognition of long-established information on the commensal microbiota of mammals, as well as that of recent molecular understanding of the genetic agents involved in the movement of resistance genes.

The assessment and management of burns

Each year many people seek medical advice or hospital treatment for burn or scald injuries. There is limited data on the number of burns patients seen in primary care, however a recent national survey suggested that there are 250,000 presentations of burn injuries to primary care teams in the UK per year (National Burn Care Review, 2001). This article discusses the nursing management of burns in the community, outlining the initial assessment of the burns patient in terms of trauma management, and focusing primarily on those patients with non-complex burns. A full patient assessment incorporates the patient's general condition, the type, cause, depth and extent of the burn and the effects on the individual patient. Good patient management is an essential element of care and the focus of this is the management of pain, prevention of infection, provision of evidence based wound care and onward referrals as appropriate. However not all patients can be managed solely in the community and the nurse needs to know when to refer and to whom to refer. The article outlines the recommendations from the National Burn Care Review in terms of patient referral.

Case 40: ward management. Ward sister who failed to manage her ward appropriately

This article reviews the factors that impinge on the application of topical medications in wound care. The role of systemic and topical antibiotics in wound care is reviewed. Similarly, two antiseptics — iodine and silver, of great current interest in wound management — are scrutinized. The value of these topical agents in the management of wound bioburden should be ascertained from the perspective of understanding the advantages and disadvantages of their use and not established from what is currently the trend.

Antiseptics and disinfectants: activity, action, and resistance

Antiseptics and disinfectants are extensively used in hospitals and other health care settings for a variety of topical and hard-surface applications. A wide variety of active chemical agents (biocides) are found in these products, many of which have been used for hundreds of years, including alcohols, phenols, iodine, and chlorine. Most of these active agents demonstrate broad-spectrum antimicrobial activity; however, little is known about the mode of action of these agents in comparison to antibiotics. This review considers what is known about the mode of action and spectrum of activity of antiseptics and disinfectants. The widespread use of these products has prompted some speculation on the development of microbial resistance, in particular whether antibiotic resistance is induced by antiseptics or disinfectants. Known mechanisms of microbial resistance (both intrinsic and acquired) to biocides are reviewed, with emphasis on the clinical implications of these reports.

Evaluation of the penetration strength, bactericidal efficacy and spectrum of action of several antimicrobial creams against isolated microorganisms in a burn centre

The antibacterial activity of eight antiseptic creams: 1 per cent silver sulphadiazine; 0.2 per cent nitrofurazone; 0.1, 0.5 and 1 per cent chlorhexidine; 2.2 per cent cerium nitrate; 10 per cent povidone iodine; and 1 per cent silver sulphadiazine with 2.2 per cent cerium nitrate were evaluated in vitro. The evaluation included the minimum inhibitory concentration (MIC) against 100 microorganisms isolated from burn patients, the chronology of the bacterial activity against Ps. aeruginosa and Staph. aureus and the penetration strength of the creams through a novel in vitro model contaminated with 17 microorganisms of different species isolated from burn patients. The results revealed that 0.5 per cent or 1 per cent chlorhexidine, 2.2 per cent cerium nitrate, and 1 per cent silver sulphadiazine with 2.2 per cent cerium nitrate were the creams which were effective at the highest dilutions. 0.5 per cent chlorhexidine and 10 per cent povidone iodine had the greater bactericidal activity. Finally, 0.2 per cent nitrofurazone showed greater penetration strength within the eschar model in comparison with the weaker penetration of 0.5 per cent and 1 per cent chlorhexidine and the absence of penetration by the rest of the antibacterial creams.

An evaluation of the antibacterial activities of combinations of sulfonamides, trimethoprim, dibromopropamidine, and silver nitrate compared with their uptakes by selected bacteria

Modifications of antibacterial activity have been demonstrated using combinations of two antibacterials from trimethoprim, sulfonamides (sulfadiazine, sulfamerazine, and silver sulfadiazine), silver nitrate, and dibromopropamidine isethionate, either formulated in a cream base or dissolved in peptone water. The creams were evaluated using the agar cup diffusion method in isosensitest agar. The peptone water solutions provided fractional inhibitory concentrations for combinations of the antibacterial substances. The test organisms were Pseudomonas aeruginosa, Enterobacter cloacae, and Staphylococcus aureus. Bacterial uptakes of antibacterial combinations, determined by either an HPLC assay method or an atomic absorption method, combined with dry cell weight determinations, indicated that enhancement of activity of the antibacterial combinations against P. aeruginosa (two strains) and E. cloacae were related to marked increases in the bacterial uptake of the chemical agents. Decreases in activity were related to decreased uptake of either dibromopropamidine and/or silver ions. The effect of the trimethoprim and the sulfonamides was shown to depend on their effect on bacterial folate synthesis. It is suggested that partial blockade of the folate synthetic pathway leads to an effect on cell permeability which results in increased uptake of antibacterials. Dibromopropamidine isethionate also has an effect on cell permeability which produces an increased bacterial uptake of a second antibacterial present in the medium. These findings provide further explanation of how subinhibitory concentrations of trimethoprim and sulfonamide combinations are synergistic against a wide range of bacteria even when certain bacteria are resistant to either member of the combination.

Factors influencing the performance of temporary skin substitutes

Advances in our knowledge of the wound healing process has led to the development of various synthetic skin substitutes, which when applied to the wound surface provide a microclimate conducive to healing. The requirements of an ideal temporary skin substitute are presented. This review also provides an updated account of the preclinical evaluation procedures utilized to assess these demands, particularly important parameters such as water vapour permeability, adherence to excised wound surface, oxygen permeability, mechanical properties, microbial permeability and exudate soaking capacity.

Plasticized polyvinyl chloride film as a primary burns dressing: a microbiological study

Twenty-four patients were studied after the application of plasticized polyvinyl chloride (PVC) film as a temporary burns dressing. The burns were assessed as being partial thickness (nine patients) and full thickness (15 patients) in depth and involving 2 per cent to 35 per cent of the body surface area. Microbiological cultures were performed on the exudate beneath the plasticized PVC film and then at each dressing change until the burn was healed. Bacterial isolates showed no unexpected organisms and there was no predominant organism to suggest contamination from the plasticized PVC film. Indeed, bacteria were only rarely isolated from the initial exudate (three of 37 burn wounds), and subsequent bacterial cultures did not differ from those normally found in burn wounds. In addition, incorporation of the plasticized PVC film into nutrient broth and agar with Staph, aureus and Ps. aeruginosa did not influence the recovery of these organisms, indicating that plasticized PVC film does not exert any antibacterial effect.

Experimental study on topical antimicrobial agents in burns

Numerous organic silver salts have been tested against a virulent strain of Pseudomonas aeruginosa which had been deliberately applied to the scalded tails of mice and deeper scald wounds on the backs of rabbits. Silver pipemidate was found to be more effective than silver sulphadiazine in treating these infected wounds.

Topical therapy for burns

Topical antimicrobial agents can prevent or minimize burn infections and should be used from the outset in all patients who are at significant risk from sepsis--either because of their wound severity or associated comorbid factors. All of the currently available topical agents have shortcomings; some of them have appreciable toxicity. The recent shift in emphasis toward early surgical closure of extensive deep burns in great part has resulted from appreciation of the inadequacies of currently available topical agents. Topical agents cannot substitute for timely and comprehensive physiologic support of burned patients.

Antimicrobial cream susceptibility testing

Utilizing a recently described rapid needle extrusion method for determining the sensitivities of burn wound isolates, we have compiled data on the resistance patterns of over 250 isolates from our burn unit. Major isolate groups were Staphylococcus aureus, Pseudomonas aeruginosa, various Enterobacteriaceae and Enterococci. Excellent correlation was exhibited between the inhibitory zone sizes and the minimal inhibitory concentration for 120 organisms tested. Utilizing the needle extrusion sensitivities to facilitate the selection of the burn creams, a significant reduction in the microbiologic flora of the burn wound was noted. The utilization of this technique in the selection of burn creams deserves controlled trials to assess whether changes in topical therapy might alter clinical outcome.

Tissue deposition of silver following topical use of silver sulphadiazine in extensive burns

Silver sulphadiazine has been applied to the burn wounds of 509 patients during the past 10 years. Eleven patients with burns covering more than 20 per cent of the body surface showed silver deposits in the mucosa of the lips, gingiva and cheeks. The colour of the burn wound was also slightly darker than in patients not treated with silver compounds. This darker colour spontaneously disappeared during the year following discharge from hospital. The pathogenesis of silver deposition has been discussed in relation to other published studies.

Protection against Pseudomonas aeruginosa infection in a murine burn wound sepsis model by passive transfer of antitoxin A, antielastase, and antilipopolysaccharide

The protective capacity of passively transferred immunoglobulin G (IgG) fractions from antitoxin (AT-IgG), antielastase (AE-IgG), and antilipopolysaccharide (ALPS-IgG) against Pseudomonas aeruginosa infection was evaluated in a murine burn wound sepsis model. Complete protection was afforded by homologous ALPS-IgG against intermediate challenge doses (10 50% lethal doses) of P. aeruginosa PA220, whereas AT-IgG and AE-IgG offered no significant protection (P less than 0.5). The simultaneous transfer of AT-IgG or AE-IgG with ALPS-IgG gave no additional protection above that seen with ALPS-IgG alone. The transfer of ALPS-IgG did not dramatically alter bacterial multiplication in the skin at the site of infection. However, bacteremia and infection of the liver were prevented. In parallel experiments, AT-IgG or AE-IgG did not significantly alter either the course of the infection or the number of bacteria seen in the blood, liver, or skin when compared with controls. ALPS-IgG administered 24 h before infection, at the time of infection, or 4 h postinfection provided complete protection. Even when ALPS-IgG was transferred at a time when the infection was well established locally in the skin (8 h postinfection), highly significant protection (P greater than 0.999) was obtained. Protection afforded by ALPS-IgG was serotype specific. These results indicate that antibody to lipopolysaccharide is of critical importance for protection against P. aeruginosa challenge in a relevant animal model.

Changing patterns of Pseudomonas aeruginosa antibiotic sensitivity

Using a sample of 71 Pseudomonas aeruginosa infected burns patients admitted to the Burns Injury Unit of the Royal Brisbane Hospital within an 11-year period the pattern of sensitivity of the organism to 18 antibiotics was studied longitudinally looking at first and last cultures (either pus, blood or sputum) separately. Only 5 antibiotics reflected a significant change (towards resistance) in sensitivity patterns (chloramphenicol, gentamycin, kanamycin, tetracycline, achromycin). Six of the other 13 antibiotics showed a trend towards increasing resistance but the changes were not statistically significant (polymyxin B, carbenicillin, sulphanomides, cotrimoxazole, streptomycin, teramycin). The other 7 antibiotics showed no change, all but one (colistin) being resistant throughout.

Controlled trials of a polyvalent pseudomonas vaccine in burns

A polyvalent pseudomonas vaccine has been tested in controlled clinical trials at two burns units, in Birmingham and New Delhi, in children and adults with burns more than 15% full skin thickness. None of the vaccinated patients in either trial showed blood cultures containing Pseudomonas aeruginosa, and vaccinees showed raised titres of protective antibody and increased phagocytic activity against Ps. aeruginosa. In the New Delhi unit, where death from Ps. aeruginosa infection is common, the mortality in adults was reduced from 40.6% (13/32) in the unvaccinated group to 6.6% (2/30) in the vaccinated group, and in children from 20.8% (5/24) in the unvaccinated group to 4.8% (1/21) in the vaccinated group.

Gentamicin- and silver-resistant pseudomonas in a burns unit

In 1977-8 gentamicin-resistant strains of Pseudomonas aeruginosa became very common in a burns unit, over 90% being resistant at the peak of the outbreak. Some strains were also resistant to silver nitrate, though silver resistance was not found in any other strains of Ps aeruginosa isolated. Unlike the gentamicin resistance, the silver resistance was unstable, and strains became sensitive on repeated subculture. All the gentamicin-resistant strains of Ps aeruginosa were of the same serotype (O:11, H:2,5). Though gentamicin resistance could be transferred in vitro from resistant strains of Ps aeruginosa to one sensitive strain of Ps aeruginosa, there was no evidence of in-vivo transfer of gentamicin resistance between strains of pseudomonas in the patients' burns, nor was there evidence of transfer of gentamicin resistance between Ps aeruginosa and enterobacteria. Carbenicillin-resistant and gentamicin-resistant Ps aeruginosa were sometimes found in the same burns, but no gentamicin-carbenicillin (doubly) resistant strains were found among the 986 strains tested during the outbreak. The outbreak of gentamicin-resistant Ps aeruginosa from burns was not reduced by stopping treatment with gentamicin and its analogues but only by segregating all patients with Ps aeruginosa in one of the two wards of the unit and admitting new patients only to the other ward.

Clinical comparison of maphenide and silver sulphadiazine

A series of 645 consecutive burn injuries are analysed. There were 175 patients in the control group, 156 in the Maphenide (Sulfamylon) group and 314 in the Silver Sulphadiazine (S. S. D.) group. The Maphenide group and S.S.D. group are compared statistically with the control group. S.S.D. proved superior in relation to clinical infection rate and culture rate in reduction of Pseudomonas and Staphylococcus. Other culture rates were analysed. There were significant reductions in both groups for E. coli and Candida albicans. Pneumonias were significantly increased in both groups and the mortality rate reduced with S.S.D. Overall S.S.D. gave better results than Maphenide.