Antiseptic and aseptic prophylaxis for burns: use of silver nitrate and of isolators

Disinfectants and antiseptics: mechanisms of action and resistance

Chemical biocides are used for the prevention and control of infection in health care, targeted home hygiene or controlling microbial contamination for various industrial processes including but not limited to food, water and petroleum. However, their use has substantially increased since the implementation of programmes to control outbreaks of methicillin-resistant Staphylococcus aureus, Clostridioides difficile and severe acute respiratory syndrome coronavirus 2. Biocides interact with multiple targets on the bacterial cells. The number of targets affected and the severity of damage will result in an irreversible bactericidal effect or a reversible bacteriostatic one. Most biocides primarily target the cytoplasmic membrane and enzymes, although the specific bactericidal mechanisms vary among different biocide chemistries. Inappropriate usage or low concentrations of a biocide may act as a stressor while not killing bacterial pathogens, potentially leading to antimicrobial resistance. Biocides can also promote the transfer of antimicrobial resistance genes. In this Review, we explore our current understanding of the mechanisms of action of biocides, the bacterial resistance mechanisms encompassing both intrinsic and acquired resistance and the influence of bacterial biofilms on resistance. We also consider the impact of bacteria that survive biocide exposure in environmental and clinical contexts.

Targeting Plasmids to Limit Acquisition and Transmission of Antimicrobial Resistance

Antimicrobial resistance (AMR) is a significant global threat to both public health and the environment. The emergence and expansion of AMR is sustained by the enormous diversity and mobility of antimicrobial resistance genes (ARGs). Different mechanisms of horizontal gene transfer (HGT), including conjugation, transduction, and transformation, have facilitated the accumulation and dissemination of ARGs in Gram-negative and Gram-positive bacteria. This has resulted in the development of multidrug resistance in some bacteria. The most clinically significant ARGs are usually located on different mobile genetic elements (MGEs) that can move intracellularly (between the bacterial chromosome and plasmids) or intercellularly (within the same species or between different species or genera). Resistance plasmids play a central role both in HGT and as support elements for other MGEs, in which ARGs are assembled by transposition and recombination mechanisms. Considering the crucial role of MGEs in the acquisition and transmission of ARGs, a potential strategy to control AMR is to eliminate MGEs. This review discusses current progress on the development of chemical and biological approaches for the elimination of ARG carriers.

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.

Antiseptics for burns

BACKGROUND

Burn wounds cause high levels of morbidity and mortality worldwide. People with burns are particularly vulnerable to infections; over 75% of all burn deaths (after initial resuscitation) result from infection. Antiseptics are topical agents that act to prevent growth of micro-organisms. A wide range are used with the intention of preventing infection and promoting healing of burn wounds.

OBJECTIVES

To assess the effects and safety of antiseptics for the treatment of burns in any care setting.

SEARCH METHODS

In September 2016 we searched the Cochrane Wounds Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), Ovid MEDLINE, Ovid MEDLINE (In-Process & Other Non-Indexed Citations), Ovid Embase, and EBSCO CINAHL. We also searched three clinical trials registries and references of included studies and relevant systematic reviews. There were no restrictions based on language, date of publication or study setting.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that enrolled people with any burn wound and assessed the use of a topical treatment with antiseptic properties.

DATA COLLECTION AND ANALYSIS

Two review authors independently performed study selection, risk of bias assessment and data extraction.

MAIN RESULTS

We included 56 RCTs with 5807 randomised participants. Almost all trials had poorly reported methodology, meaning that it is unclear whether they were at high risk of bias. In many cases the primary review outcomes, wound healing and infection, were not reported, or were reported incompletely.Most trials enrolled people with recent burns, described as second-degree and less than 40% of total body surface area; most participants were adults. Antiseptic agents assessed were: silver-based, honey, Aloe Vera, iodine-based, chlorhexidine or polyhexanide (biguanides), sodium hypochlorite, merbromin, ethacridine lactate, cerium nitrate and Arnebia euchroma. Most studies compared antiseptic with a topical antibiotic, primarily silver sulfadiazine (SSD); others compared antiseptic with a non-antibacterial treatment or another antiseptic. Most evidence was assessed as low or very low certainty, often because of imprecision resulting from few participants, low event rates, or both, often in single studies. Antiseptics versus topical antibioticsCompared with the topical antibiotic, SSD, there is low certainty evidence that, on average, there is no clear difference in the hazard of healing (chance of healing over time), between silver-based antiseptics and SSD (HR 1.25, 95% CI 0.94 to 1.67; I² = 0%; 3 studies; 259 participants); silver-based antiseptics may, on average, increase the number of healing events over 21 or 28 days' follow-up (RR 1.17 95% CI 1.00 to 1.37; I² = 45%; 5 studies; 408 participants) and may, on average, reduce mean time to healing (difference in means -3.33 days; 95% CI -4.96 to -1.70; I² = 87%; 10 studies; 979 participants).There is moderate certainty evidence that, on average, burns treated with honey are probably more likely to heal over time compared with topical antibiotics (HR 2.45, 95% CI 1.71 to 3.52; I² = 66%; 5 studies; 140 participants).There is low certainty evidence from single trials that sodium hypochlorite may, on average, slightly reduce mean time to healing compared with SSD (difference in means -2.10 days, 95% CI -3.87 to -0.33, 10 participants (20 burns)) as may merbromin compared with zinc sulfadiazine (difference in means -3.48 days, 95% CI -6.85 to -0.11, 50 relevant participants). Other comparisons with low or very low certainty evidence did not find clear differences between groups.Most comparisons did not report data on infection. Based on the available data we cannot be certain if antiseptic treatments increase or reduce the risk of infection compared with topical antibiotics (very low certainty evidence). Antiseptics versus alternative antisepticsThere may be some reduction in mean time to healing for wounds treated with povidone iodine compared with chlorhexidine (MD -2.21 days, 95% CI 0.34 to 4.08). Other evidence showed no clear differences and is of low or very low certainty. Antiseptics versus non-antibacterial comparatorsWe found high certainty evidence that treating burns with honey, on average, reduced mean times to healing in comparison with non-antibacterial treatments (difference in means -5.3 days, 95% CI -6.30 to -4.34; I² = 71%; 4 studies; 1156 participants) but this comparison included some unconventional treatments such as amniotic membrane and potato peel. There is moderate certainty evidence that honey probably also increases the likelihood of wounds healing over time compared to unconventional anti-bacterial treatments (HR 2.86, 95% C 1.60 to 5.11; I² = 50%; 2 studies; 154 participants).There is moderate certainty evidence that, on average, burns treated with nanocrystalline silver dressings probably have a slightly shorter mean time to healing than those treated with Vaseline gauze (difference in means -3.49 days, 95% CI -4.46 to -2.52; I² = 0%; 2 studies, 204 participants), but low certainty evidence that there may be little or no difference in numbers of healing events at 14 days between burns treated with silver xenograft or paraffin gauze (RR 1.13, 95% CI 0.59 to 2.16 1 study; 32 participants). Other comparisons represented low or very low certainty evidence.It is uncertain whether infection rates in burns treated with either silver-based antiseptics or honey differ compared with non-antimicrobial treatments (very low certainty evidence). There is probably no difference in infection rates between an iodine-based treatment compared with moist exposed burn ointment (moderate certainty evidence). It is also uncertain whether infection rates differ for SSD plus cerium nitrate, compared with SSD alone (low certainty evidence).Mortality was low where reported. Most comparisons provided low certainty evidence that there may be little or no difference between many treatments. There may be fewer deaths in groups treated with cerium nitrate plus SSD compared with SSD alone (RR 0.22, 95% CI 0.05 to 0.99; I² = 0%, 2 studies, 214 participants) (low certainty evidence).

AUTHORS' CONCLUSIONS

It was often uncertain whether antiseptics were associated with any difference in healing, infections, or other outcomes. Where there is moderate or high certainty evidence, decision makers need to consider the applicability of the evidence from the comparison to their patients. Reporting was poor, to the extent that we are not confident that most trials are free from risk of bias.

Evidence-based Practices in Infection Control

Abstract Evidence can be obtained from clinical trials and bacteriological studies. The latter consist mainly of measuring reductions in colonization, or reductions in bacterial counts on naturally or artificially contaminated surfaces, following the introduction of the measure to be tested. Controlled clinical trials usually provide the best evidence, but are infrequently carried out due to the large number of subjects required, low initial infection rates and a multiplicity of associated factors. Bacteriological studies can be carried out more easily and can often provide statistically significant results not readily available in clinical studies, but they require care in interpretation. Studies involving bacterial counts in the inanimate environment are particularly likely to give misleading results, but have often provided useful confirmatory evidence in eliminating rituals.

Orthopaedic device-related infection: current and future interventions for improved prevention and treatment

Orthopaedic and trauma device-related infection (ODRI) remains one of the major complications in modern trauma and orthopaedic surgery.Despite best practice in medical and surgical management, neither prophylaxis nor treatment of ODRI is effective in all cases, leading to infections that negatively impact clinical outcome and significantly increase healthcare expenditure.The following review summarises the microbiological profile of modern ODRI, the impact antibiotic resistance has on treatment outcomes, and some of the principles and weaknesses of the current systemic and local antibiotic delivery strategies.The emerging novel strategies aimed at preventing or treating ODRI will be reviewed. Particular attention will be paid to the potential for clinical impact in the coming decades, when such interventions are likely to be critically important.The review focuses on this problem from an interdisciplinary perspective, including basic science innovations and best practice in infectious disease. Cite this article: Moriarty TF, Kuehl R, Coenye T, et al. Orthopaedic device related infection: current and future interventions for improved prevention and treatment. EFORT Open Rev 2016;1:89-99. DOI: 10.1302/2058-5241.1.000037.

Green and ecofriendly synthesis of silver nanoparticles: Characterization, biocompatibility studies and gel formulation for treatment of infections in burns

The current study summarizes a unique green process for the synthesis of silver nanoparticles (AgNPs) by simple treatment of silver nitrate with aqueous extract of Ammania baccifera. Phytosynthesized AgNPs were characterized by various advanced analytical methods and studied for its use against infections associated with burns. Formation of AgNPs was observed by visual color change from colorless to dark brown and confirmed by UV-visible characteristic peak at 436 nm. Zeta potential, particle size and polydispersity index of nano-silver were found to be -33.1 ± 1.12, 112.6 ± 6.8 nm and 0.3 ± 0.06 respectively. XRD spectra revealed crystalline nature of AgNPs whereas TEM confirmed the presence of mixed morphology of AgNPs. The overall approach designated in the present research investigation for the synthesis of AgNPs is based on all 12 principles of green chemistry, in which no man-made chemical other than the silver nitrate was used. Synthesized nano-silver colloidal dispersion was initially tested for minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) against a panel of organisms involved in infections associated with burns (Pseudomonas aeruginosa (PA), Staphylococcus aureus (SA) and methicillin resistant S. aureus (MRSA)). MIC and MBC were found to be in range of 0.992 to 7.93 and 7.93 to 31.75 μg/mL respectively. MBC was used for formulation of AgNP gel and tested for its efficacy using agar well diffusion method against PA, SA and MRSA. Comparative bactericidal efficacy of formulated gel (0.03% w/w) and marked formulation Silverex™ ionic (silver nitrate gel 0.2% w/w) showed equal zone of inhibition against all pathogenic bacteria. Formulated AgNP gel consisting of 95% lesser concentration of silver compared to marketed formulation was found to be equally effective against all organisms. Hence, the formulated AgNP gel could serve as a better alternative with least toxicity towards the treatment presently available for infections in burns.

Management of open wounds: lessons from orthopedic oncology

The management of complex wounds remains a challenge, and although there have been many promising advances, patients often undergo a morbid and lengthy process to obtain sufficient, satisfactory healing. Sarcoma patients are especially vulnerable to soft tissue wound-healing complications. These patients are often treated with neoadjuvant radiation and/or chemotherapy and have compromised local vascularity to healing tissue. The advent and refinement of wound vacuum-assisted closure technology have been shown to have a tremendous impact. This article reviews the benefits of some novel technologies currently undergoing investigation in orthopedic oncology that will likely have applications in wound management from other causes.

Antibiotic prophylaxis for preventing burn wound infection

BACKGROUND

Infection of burn wounds is a serious problem because it can delay healing, increase scarring and invasive infection may result in the death of the patient. Antibiotic prophylaxis is one of several interventions that may prevent burn wound infection and protect the burned patient from invasive infections.

OBJECTIVES

To assess the effects of antibiotic prophylaxis on rates of burn wound infection.

SEARCH METHODS

In January 2013 we searched the Wounds Group Specialised Register; The Cochrane Central Register of Controlled Trials (CENTRAL); Ovid MEDLINE; Ovid MEDLINE - In-Process & Other Non-Indexed Citations (2013); Ovid EMBASE; EBSCO CINAHL and reference lists of relevant articles. There were no restrictions with respect to language, date of publication or study setting.

SELECTION CRITERIA

All randomised controlled trials (RCTs) that evaluated the efficacy and safety of antibiotic prophylaxis for the prevention of BWI. Quasi-randomised studies were excluded.

DATA COLLECTION AND ANALYSIS

Two review authors independently selected studies, assessed the risk of bias, and extracted relevant data. Risk ratio (RR) and mean difference (MD) were estimated for dichotomous data and continuous data, respectively. When sufficient numbers of comparable RCTs were available, trials were pooled in a meta-analysis to estimate the combined effect.

MAIN RESULTS

This review includes 36 RCTs (2117 participants); twenty six (72%) evaluated topical antibiotics, seven evaluated systemic antibiotics (four of these administered the antibiotic perioperatively and three administered upon hospital admission or during routine treatment), two evaluated prophylaxis with non absorbable antibiotics, and one evaluated local antibiotics administered via the airway.The 11 trials (645 participants) that evaluated topical prophylaxis with silver sulfadiazine were pooled in a meta analysis. There was a statistically significant increase in burn wound infection associated with silver sulfadiazine compared with dressings/skin substitute (OR = 1.87; 95% CI: 1.09 to 3.19, I(2) = 0%). These trials were at high, or unclear, risk of bias. Silver sulfadiazine was also associated with significantly longer length of hospital stay compared with dressings/skin substitute (MD = 2.11 days; 95% CI: 1.93 to 2.28).Systemic antibiotic prophylaxis in non-surgical patients was evaluated in three trials (119 participants) and there was no evidence of an effect on rates of burn wound infection. Systemic antibiotics (trimethoprim-sulfamethoxazole) were associated with a significant reduction in pneumonia (only one trial, 40 participants) (RR = 0.18; 95% CI: 0.05 to 0.72) but not sepsis (two trials 59 participants) (RR = 0.43; 95% CI: 0.12 to 1.61).Perioperative systemic antibiotic prophylaxis had no effect on any of the outcomes of this review.Selective decontamination of the digestive tract with non-absorbable antibiotics had no significant effect on rates of all types of infection (2 trials, 140 participants). Moreover, there was a statistically significant increase in rates of MRSA associated with use of non-absorbable antibiotics plus cefotaxime compared with placebo (RR = 2.22; 95% CI: 1.21 to 4.07).There was no evidence of a difference in mortality or rates of sepsis with local airway antibiotic prophylaxis compared with placebo (only one trial, 30 participants).

AUTHORS' CONCLUSIONS

The conclusions we are able to draw regarding the effects of prophylactic antibiotics in people with burns are limited by the volume and quality of the existing research (largely small numbers of small studies at unclear or high risk of bias for each comparison). The largest volume of evidence suggests that topical silver sulfadiazine is associated with a significant increase in rates of burn wound infection and increased length of hospital stay compared with dressings or skin substitutes; this evidence is at unclear or high risk of bias. Currently the effects of other forms of antibiotic prophylaxis on burn wound infection are unclear. One small study reported a reduction in incidence of pneumonia associated with a specific systematic antibiotic regimen.

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.

Activity of topical antimicrobial agents against multidrug-resistant bacteria recovered from burn patients

BACKGROUND

Topical antimicrobials are employed for prophylaxis and treatment of burn wound infections despite no established susceptibility breakpoints, which are becoming vital in an era of multidrug-resistant (MDR) bacteria. We compared two methods of determining topical antimicrobial susceptibilities.

METHODS

Isolates of Pseudomonas aeruginosa, methicillin-resistant Staphylococcus aureus (MRSA), extended spectrum beta-lactamase (ESBL) producing Klebsiella pneumoniae, and Acinetobacter baumanii-calcoaceticus (ABC) from burn patients were tested using broth microdilution and agar well diffusion to determine minimum inhibitory concentrations (MICs) and zones of inhibition (ZI). Isolates had systemic antibiotic resistance and clonality determined. MDR included resistance to antibiotics in three or more classes.

RESULTS

We assessed 22 ESBL-producing K. pneumoniae, 20 ABC (75% MDR), 20 P. aeruginosa (45% MDR), and 20 MRSA isolates. The most active agents were mupirocin for MRSA and mafenide acetate for the gram-negatives with moderate MICs/ZI found with silver sulfadiazene, silver nitrate, and honey. MDR and non-MDR isolates had similar topical resistance. There was no clonality associated with resistance patterns.

CONCLUSION

Despite several methods to test bacteria for topical susceptibility, no defined breakpoints exist and standards need to be established. We recommend continuing to use silver products for prophylaxis against gram-negatives and mafenide acetate for treatment, and mupirocin for MRSA.

Antimicrobial effect of oxidized cellulose salts

Antimicrobial properties of oxidized cellulose and its salts in linters (-L) and microsphere (-M) form (OKCEL H-L, OKCEL Zn-M, OKCEL ZnNa-L, OKCEL ZnNa-M and OKCEL Ag-L) were tested by a dilution method against a spectrum of microbial strains: Escherichia coli, Pseudomonas aeruginosa, Staphylococcus epidermidis, Bacillus licheniformis, Aspergillus niger, Penicillium chrysogenum, Rhizopus oryzae, Scopulariopsis brevicaulis, Candida albicans and Candida tropicalis. OKCEL Ag-L exhibited antimicrobial activity in the range 0.1-3.5% w/v against all the bacteria and fungi involved in this study. Strong inhibition by OKCEL ZnNa-M was observed for Staphylococcus epidermidis, Bacillus licheniformis, Rhizopus oryzae, Candida albicans and Candida tropicalis in the range 0.5-2.0% w/v. Antimicrobial effects of oxidized cellulose and its salts in textile form were investigated by a diffusion and dilution method against the spectrum of above-cited microbial strains extended by Clostridium perfringens. Generally, OKCEL Ag-T, OKCEL Zn-T and OKCEL H-T showed high antimicrobial activity against populations of Pseudomonas aeruginosa, Bacillus licheniformis and Staphylococcus epidermidis. OKCEL Zn-T was the only sample suppressing the growth of species.

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.

Silver nitrate cautery in aphthous stomatitis: a randomized controlled trial

BACKGROUND

Aphthous stomatitis is a painful, recurrent disease of the oral mucous membrane. Silver nitrate sticks have been used for a long time to provide pain relief for the duration of an aphthous ulceration, with only one application. Silver nitrate causes chemical cauterization and increases the depth of injury.

OBJECTIVES

To study the effect of chemical cautery with silver nitrate in reducing pain of aphthous ulceration and to determine if this treatment shortens or prolongs healing.

METHODS

In a randomized, patient-blinded, placebo-controlled study, 97 patients with painful minor oral aphthous ulceration were randomized to receive silver nitrate cautery or placebo. The severity of pain was rated on a three-category scale (severe, mild, none) and was recorded each day until the seventh day after the procedure. The lesion size was recorded at the time of the procedure and on the seventh day afterwards. In the treatment group, the ulcer was gently painted with a silver nitrate stick until it turned white. In the placebo group, the ulcer was gently painted with a placebo stick.

RESULTS

In the treatment group, 33 of 47 patients (70%) evaluated and in the placebo group, four of 38 patients (11%) evaluated had reduction in severity of pain 1 day after the procedure. The difference was statistically significant (P < 0.001). On the seventh day after the procedure, the ulcers were completely re-epithelialized in 39 patients (83%) in the treatment group and in 34 patients (89%) in the placebo group. The difference was not statistically significant (P = 0.39).

CONCLUSIONS

The results of our study showed that one application of silver nitrate can decrease the severity of pain in aphthous ulceration without significantly shortening or prolonging healing time. We did not observe any side-effects in our study. The effect is rapid and lasts for the duration of the lesion. The treatment is simple and cost-effective in patients with infrequent recurrences.

The epidemiology of burn wound infections: then and now

Burn wound infections are a serious complication of thermal injury. Although pneumonia is now the most important infection in patients with burns, burn wound infection remains a serious complication unique to the burn recipient. The methods for managing thermal injury have evolved during the past 50 years. This evolution has been accompanied by changes in the etiology, epidemiology, and approach to prevention of burn wound infections. In the 1950s, 1960s, and 1970s and into the mid-1980s, burn wounds were treated by the exposure method, with application of topical antimicrobials to the burn wound surface and gradual debridement with immersion hydrotherapy. As early burn wound excision and wound closure became the focal point of burn wound management, accompanied by a change from immersion hydrotherapy to showering hydrotherapy, the rate of burn wound infection appeared to decrease. Few epidemiologic studies have been done since this change in the approach to management of thermal injury. There are few data on the epidemiology of burn wound infections from the era of early excision and closure. Data are needed on infection rates for excised and closed burn wounds, the etiologies of these infections, and the epidemiology and the prevention of such infections. Additional studies are needed on the indications for topical and antimicrobial prophylaxis and selective decontamination of the digestive tract.

Silver. I: Its antibacterial properties and mechanism of action

Silver products have two key advantages: they are broad-spectrum antibiotics and are not yet associated with drug resistance. This article, the first in a two-part series, describes the main mechanism of action of this metallic element.

Microbiological contamination of drinking water in a commercial household water filter system

The microbiological quality of filtered water in a commercial water filter system (Brita) was tested in households and in two laboratories. In 24 of 34 filters used in households, bacterial counts increased in the filtered water up to 6,000 cfu/ml. In 4 of 6 filters tested in the laboratory, bacterial counts in the fresh filtrate were higher than in tap water after approximately one week of use both at room temperature and at 4 degrees C, suggesting growth or biofilm formation in the filter material. In some cases colony counts in the filtered water were 10,000 times those in tap water. The filter material of 5 of 13 new commercial filters was contaminated with bacteria or moulds. National or international regulatory agencies should ensure that water filters marketed for domestic use do not allow deterioration in the microbiological quality of drinking water.

Physiological and toxicological changes in the skin resulting from the action and interaction of metal ions

The human environment contains more than 50 metal or metalloid elements. At least 15 are recognized as trace elements, with zinc, calcium, copper, magnesium, and iron having specific roles in skin morphogenesis and function. The present review focuses on the presumed role of metal ions in the skin, their competition for carrier proteins, and membrane receptors. Evidence presented shows that the balance of trace metal ions is critical for normal skin and repair mechanisms following injury. Xenobiotic ions can impair this balance, leading to pathological change. The skin acts as an organ of elimination of excess trace metals and xenobiotic ions from the body, but mechanisms of voidance vary for different metals. Metal ions are an important cause of allergies, and evidence is presented to show that the majority of metals or metal compounds can induce allergic changes. Except for chromium and nickel, which are among the most common human allergens, animal models have provided little information. At least cadmium, thorium, lead, chromium, nickel, beryllium, and arsenic and proven or putative carcinogens in animals or humans on the basis of cytological or epidemiological evidence. However, only arsenic exhibits a clear predilection for the skin. Other metals such as gold can induce subcutaneous sarcoma following injection, but the relevance of this observation in terms of human occupational risk is discounted.

An epidemiological study assessing the relative importance of airborne and direct contact transmission of microorganisms in a medical intensive care unit

A prospective epidemiological survey was carried out over a period of seven weeks in a medical intensive care unit. Bacteria from patients, staff and air were monitored and the transmission of isolated microorganisms was followed. Handwashing samples revealed pathogenic bacteria in 30.8% of physicians (average number of colony forming units: 71,300 per hand) and 16.6% of nurses (39,800 cfu per hand). Air cultures yielded pathogens in 15% of sampling periods and nine of 53 patients were found to be colonized with Gram-negative bacteria, Staphylococcus aureus or Candida spp. The spectrum of bacteria recovered from patients and air was generally different, whereas strains recovered from patients and their attendants' hands were indistinguishable on multiple occasions. The results of this study confirm that direct contact is the principal pathway of microbial transmission, whereas little evidence for a significant role of airborne transmission is shown. The call for more extensive air-filtering and ventilation systems in medical intensive care units is not supported by the results shown in this communication.

Heavy metal resistance in clinical isolates of Pseudomonas aeruginosa

One hundred clinical isolates of Pseudomonas aeruginosa were checked for their sensitivity towards silver nitrate. Majority of the isolates were resistant at 20 mg/L and the resistance decreased with increasing concentration of silver nitrate, only 5% of the organisms showed resistance above 70 mg/L. These silver-resistant isolates were further checked for their resistance towards mercury and cadmium at 20 mg/L of concentration and the level of resistance was found to be 33 and 40%, respectively. A correlation between silver ion resistance and concurrent mercury and cadmium ion resistance was observed, suggesting a possible linkage between resistance towards various metal ions.

Infection control during neutropenia

The first principle of infection prevention in neutropenic patients is to ensure that every effort is made to prevent impairment of the host's defences or any disturbance of the ecological balance of the patient's microbial flora. The second principle is that potential or established sources of infection should be sought and ideally treated before any immunosuppressive therapy is instituted. The third principle is to define the extent to which a particular patient can be expected to benefit from special measures such as protective isolation, sterile or low-pathogen food, decontamination, granulocyte transfusions, passive or active immunization, or antimicrobial prophylaxis aimed at a specific micro-organism such as Pneumocystis carinii or Mycobacterium tuberculosis. A programme for the prevention of infections in neutropenic patients will fail if any of these three principles is ignored.

Infections in burned patients

Prevention and treatment of burn wound infection requires knowledge of the epidemiology of such infections. Prevention of infection rests on removal of reservoirs or sources of microorganisms from the burn patient's environment and interruption of transfer of microorganisms to the surface of the wound. When prevention fails and burn wound infection develops, successful therapy may depend on an understanding of the epidemiology of the burn wound during therapy. Contrary to the oft stated concept that antibiotics penetrate the avascular burn wound poorly, our study demonstrated that gentamicin and tobramycin achieved therapeutic concentrations in burn wound tissue. As in other types of infections, susceptible microorganisms were eradicated and resistant microorganisms persisted. Of most importance was the observation that resistant microorganisms may repopulate the wound within four days of starting therapy. It would appear that failure of therapy is not due to failure of antibiotics to penetrate the burn wound but rather to rapid development of superinfection during therapy.

Evaluation of phenoxetol-chlorhexidine cream as a prophylactic antibacterial agent in burns

A controlled clinical trial was conducted to compare the value of a cream containing 2% phenoxetol and 0.2% chlorhexidine as a prophylactic agent against wound infection in patients with burns affecting up to 15% total body surface area. The acquisition of bacteria was similar in the two treatment groups but the incidence of Staphylococcus aureus in the burns treated with phenoxetol-chlorhexidine cream significantly lower. The incidence of gram-negative bacilli was low in the two treatment groups, and no wound yielded Pseudomonas aeruginosa. Unlike preparations containing silver, phenoxetol-chlorhexidine does not cause electrolyte imbalance or stain materials with which it comes into contact, and it did not produce adverse effects during this trial.

Attempts to control clothes-borne infection in a burn unit, 2. Clothing routines in clinical use and the epidemiology of cross-colonization

Previous investigations have shown that cross-contamination in a burn unit is mainly clothes-borne. New barrier garments have been designed and tried experimentally. The aim of the present study was to investigate the effects of different clothing routines on cross-contamination. In a long-term study, the rates and routes of colonizations with Staphylococcus aureus, Streptococcus groups A, B, C, F, and G and Pseudomonas aeruginosa were examined. The exogenous colonization rates were, with S. aureus 77%, with Streptococcus species 52% and with Ps. aeruginosa 32%. The colonization rate with Ps. aeruginosa was higher in patients with larger burns. Patients dispersed Streptococcus and Ps. aeruginosa as well as S. aureus into the air of their rooms in considerable amounts, but dispersers were not more important as sources of cross-colonization than non-dispersers. In comparison of clothing routines, there was no difference in overall colonization rates. The newly designed barrier garment that was made from apparently particle-tight material did not reduce the transfer of bacteria from patient to patient. A less rigid routine than that previously used did not increase the risk of cross-contamination. A thorough change of barrier dress after close contact nursing delayed the first exogenous S. aureus colonization from day 6 to day 14 after admission. This routine might be recommended for clinical use. Otherwise, methods must be developed for adequate selection of materials intended for barrier garments.

Attempts to control clothes-borne infection in a burn unit, 3. An open-roofed plastic isolator or plastic aprons to prevent contact transfer of bacteria

An open-roofed plastic isolator was built in a single patient isolation room in a burn unit. It was designed to prevent contact contamination only, as this had been shown to be the important route of cross-colonization in the unit. To exclude any possible effect on airborne transfer of bacteria, the isolator was first examined by means of an airborne particle tracer of the same size as bacteria-carrying particles. Such experiments indicated that the isolator might prevent some transfer out of but not into the isolator. This was not confirmed in simulated nursing experiments nor in a patient study, where the air counts of bacteria were practically the same inside and outside the isolator wall. Two patients only were nursed in the isolator. Both patients acquired exogenous colonizations from other patients, one with Ps. aeruginosa and the other with S. aureus. Nursing in the isolator was difficult and staff-demanding. In simulated nursing experiments, plastic aprons and gauntlets as the only protective measures against contact contamination gave as much protection to a mock patient as did the isolator. S. aureus were released from nurses' clothes more easily during work with the isolator than in open nursing with aprons and gauntlets. In conclusion, the isolator did not seem to be a realistic alternative to impermeable clothes such as plastic aprons as a means of preventing clothes-borne cross-contamination between burn patients.

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.

Isolation care of infection-prone burn patients

An experimental and clinical study of spread of colonisation between burn patients, and their susceptibility to infection, was performed. Burn patients' polymorphonuclear neutrophil granulocytes (PMN) functioned poorly, particularly during the second week after injury which coincided with maximum growth of bacteria in the burn wound. Patients with large burns often dispersed S. aureus and Ps. aeruginosa but also beta-hemolytic Streptococcus to the air of their rooms. Airborne transfer of these bacteria was practically eliminated by nursing in single isolation rooms with plenum ventilation. In such rooms, cross-contamination was carried mainly via clothes. Patients with small burns sometimes were important sources of such contamination although they dispersed little bacteria to the air. A thorough change of barrier dress after close contact nursing delayed the first exogenous S. aureus colonisation until after the time of greatest impairment in PMN functions. A further reduction in cross-contamination would be possible with barrier garments impermeable to fluids and bacteria on points of contact, as shown in experiments with plastic apron as protective dress. Measurements of penetration through fabrics of particles suspended in air, commercially used, did not correlate to the performance of garments made from the fabrics in experimental nursing and clinical use. Bacteria were shown to penetrate fabrics through rubbing, particularly when wet where the microcolonies present on the cloth were separated into smaller units. An instrument was designed which measured such penetration, and was used to select fabrics for barrier garments. Tightly fitting barrier garments increased the disperal of bacteria from clothes worn underneath them. The wearing of barrier garments should therefore be restricted to close contact nursing. An open-roofed plastic patient isolator was designed and built. It did not appreciably reduce cross-contamination and gave psychological and practical problems. It seemed not to be a realistic alternative to better protective garments in isolation rooms.