The role of melanin in Aspergillus tolerance to biocides and photosensitizers.

Cationic biocides are widely utilized for surface disinfection. Photosensitizers such as toluidine blue O (TBO) produce reactive oxygen species following light excitation and are being investigated as novel biocides for similar applications. Aspergillus brasiliensis conidia contain melanin which protects against environmental stressors. The negative charge and antioxidant properties of melanin may confer resistance to photosensitizers and other biocides. In this study, the yeasticidal and fungicidal activity benzalkonium chloride (BZC), sodium dichloroisocyanurate (NaDCC) and TBO with red light were examined using quantitative suspension tests. All three biocides were highly effective against Candida albicans and > 5·0 log10 reductions in viability were attainable within 5 minutes. Wild-type A. brasiliensis conidia were highly tolerant to treatment and 0·4 log10 reductions in viability were observed within the same time frame when treated with TBO or BZC. NaDCC was markedly more effective. Inhibition of melanin biosynthesis by culturing with 100 µg ml-1 kojic acid resulted in a hypopigmented phenotype with significantly increased sensitivity to all three biocides. These observations indicate that melanin is a significant contributor towards A. brasiliensis tolerance of biocides and photosensitizers and demonstrate that cationic biocides are poorly suited to applications where the control of A. brasiliensis is required.

Effect of Exposure to Chlorhexidine Residues at "During Use" Concentrations on Antimicrobial Susceptibility Profile, Efflux, Conjugative Plasmid Transfer, and Metabolism of Escherichia coli.

There is no standardized protocol to predict the concentration levels of microbicides that are left on surfaces as a result of the use of these products, and there is no standardized method to predict the potential risk that such levels pose to emerging antibacterial resistance. The ability to distinguish between selection and adaption processes for antimicrobial resistance in bacteria and the impact of different concentrations of microbicide exposure have not been fully investigated to date. This study considers the effect of exposure to a low concentration of chlorhexidine digluconate (CHX) on selected phenotypes of Escherichia coli and relates the findings to the risk of emerging antimicrobial resistance. A concentration of 0.006 mg/ml CHX is a realistic "during use" exposure concentration measured on surfaces. At this concentration, it was possible for CHX-susceptible bacteria to survive, adapt through metabolic alterations, exhibit a transient decrease in antimicrobial susceptibility, and express stable clinical cross-resistance to front-line antibiotics. Efflux activity was present naturally in tested isolates, and it increased in the presence of 0.00005 mg/ml CHX but ceased with 0.002 mg/ml CHX. Phenotypic microarray assays highlighted a difference in metabolic regulation at 0.00005 mg/ml and 0.002 mg/ml CHX; more changes occurred after growth with the latter concentration. Metabolic phenotype changes were observed for substrates involved with the metabolism of some amino acids, cofactors, and secondary metabolites. It was possible for one isolate to continue transferring ampicillin resistance in the presence of 0.00005 mg/ml CHX, whilst 0.002 mg/ml CHX prevented conjugative transfer. In conclusion, E. coli phenotype responses to CHX exposure are concentration dependent, with realistic residual CHX concentrations resulting in stable clinical cross-resistance to antibiotics.

Understanding the risk of emerging bacterial resistance to over the counter antibiotics in topical sore throat medicines.

AIMS: The aims of this study were to explore the development of bacterial resistance and cross-resistance in four common human pathogens following realistic exposure to antibiotics found in over-the-counter (OTC) sore throat medicines: gramicidin, neomycin, bacitracin and tyrothricin. METHODS AND RESULTS: Bacterial exposure to in-use (concentration in the product before use) and diluted concentration (i.e. during use) of antibiotic where conducted in broth for 24 h or until growth was visible. The changes in bacterial susceptibility profile before and after exposure was determined using standardized ISO microdilution broth. Antibiotic testing was performed according to EUCAST guidelines. We demonstrated that test bacteria were able to survive exposure to the in-use concentrations of some antibiotics used in OTC medicines. Exposure to during use concentrations of bacitracin resulted in stable increase in minimal inhibitory concentration (MIC) (>8-fold) in Staphylococcus aureus and Acinetobacter baumannii. Exposure to tyrothricin resulted in a stable increase in MIC (2·4-fold) in Klebsiella pneumoniae, and exposure to neomycin resulted in a stable increase MIC (5000-fold higher than the baseline) in Streptococcus pyogenes. Clinical cross-resistance to other antibiotics (ciprofloxacin, fusidic acid, gentamicin, cefpodoxime, amoxicillin/clavulanic acid and cefotaxime) was also demonstrated following exposure to bacitracin or tyrothricin. Bacitracin exposure lead to a stable bacterial resistance after 10 passages. CONCLUSIONS: Our results indicate that OTC antibiotic medicines have the potential to drive resistance and cross-resistance in vitro. SIGNIFICANCE AND IMPACT OF THE STUDY: Tackling antibiotic resistance is a high worldwide priority. It is widely accepted that the overuse and misuse of antibiotics increase the risk of the development and spread of antibiotic resistance within communities. A number of OTC sore throat products, widely available across the world for topical use in respiratory indications, contain locally delivered antibiotics. Our findings showed that these antibiotics in OTC medicines present a risk for emerging cross-resistance in a number of bacterial respiratory pathogens.

Use of a small-scale, portable test chamber for determining the bactericidal efficacy of aerosolized glycol formulations.

This study aimed to understand the efficacy and mechanisms of action of an aerosolized glycol-ethanol formulations against bacteria. We validated a small-scale in-house test chamber to determine the microbicidal efficacy of four aerosolized formulations combining dipropylene glycol and ethanol against Staphylococcus aureus and Escherichia coli embedded in alginate. The aerosolized glycol/ethanol formulation decreased bacterial viability by 3 log10 and was more efficacious than an ethanol only control formulation. Electron microscopic examination indicated extensive structural damage in both bacteria, and membrane damage was confirmed with potassium release in S. aureus and DNA release in E. coli. The development of a small test chamber facilitated the measurement of the microbicidal efficacy and experiments to understand the mechanism of action of an aerosolized microbicidal formulation. SIGNIFICANCE AND IMPACT OF THE STUDY: There is an increased interest in developing effective microbicidal-aerosolized formulations. The development of a small in-house test chamber allowed the measurement of the microbicidal efficacy of an aerosolized glycol/ethanol formulation at a low cost. We showed that a glycol/ethanol aerosolized formulation caused extensive structural damage in Gram-negative and -positive bacteria resulting in a 3 log10 reduction in viability.

Artificial dry surface biofilm models for testing the efficacy of cleaning and disinfection.

Dry surface biofilms (DSB) harbouring pathogens are widespread in healthcare settings, are difficult to detect and are resistant to cleaning and disinfection interventions. Here, we describe a practical test protocol to palliate the lack of standard efficacy test methods for DSB. Staphylococcus aureus DSB were produced over a 12-day period, grown with or without the presence of organic matter, and their composition and viability were evaluated. Disinfectant treatment was conducted with a modified ASTM2967-15 test and reduction in viability, transferability and biofilm regrowth post-treatment were measured. Dry surface biofilms produced over a 12-day period had a similar carbohydrates, proteins and DNA content, regardless of the presence or absence of organic matter. The combination of sodium hypochlorite (1000 ppm) and a microfiber cloth was only effective against DSB in the absence of organic load. With the increasing concerns of the uncontrolled presence of DSB in healthcare settings, the development of effective intervention model in the presence of organic load is appropriate for the testing of biocidal products, while the use of three parameters, log10 reduction, transferability and regrowth, provides an accurate and practical measurement of product efficacy. SIGNIFICANCE AND IMPACT OF THE STUDY: The widespread presence of biofilms on dry surfaces in healthcare settings has been recently documented. These dry surface biofilms (DSB) present an unprecedented challenge to cleaning and disinfection processes. Here, we describe a practical efficacy protocol based on an in vitro Staphylococcus aureus DSB model. The protocol measures reduction in viability, transferability and biofilm regrowth post-treatment to provide altogether a practical assessment of product efficacy against dry surface biofilms.

Assessing the activity of microbicides against bacterial spores: knowledge and pitfalls.

Bacterial endospores (spores) have a higher intrinsic resistance to microbicides as compared to other microbial forms, most likely due to their impermeable outer layers and low water content. Though structural differences between the spores of various bacterial species may account for observed variations in their resistance to microbicides, flaws in methods for testing the sporicidal activity of microbicides often exaggerate the differences. This has major implications when considering the selection of one or more surrogates to assess microbicides against clinically relevant spore-formers such as Clostridium difficile. The mounting significance of Cl. difficile as a pathogen is leading to a corresponding increase in the number of commercially available microbicidal formulations claiming activity against its spores without proper differentiation between the product's sporistatic and sporicidal actions. In this review we critically assess the situation and the implications of product claims on the field use of microbicidal products.

Phytochemical profiling as a solution to palliate disinfectant limitations.

The indiscriminate use of biocides for general disinfection has contributed to the increased incidence of antimicrobial tolerant microorganisms. This study aims to assess the potential of seven phytochemicals (tyrosol, caffeic acid, ferulic acid, cinnamaldehyde, coumaric acid, cinnamic acid and eugenol) in the control of planktonic and sessile cells of Staphylococcus aureus and Escherichia coli. Cinnamaldehyde and eugenol showed antimicrobial properties, minimum inhibitory concentrations of 3-5 and 5-12 mM and minimum bactericidal concentrations of 10-12 and 10-14 mM against S. aureus and E. coli, respectively. Cinnamic acid was able to completely control adhered bacteria with effects comparable to peracetic acid and sodium hypochlorite and it was more effective than hydrogen peroxide (all at 10 mM). This phytochemical caused significant changes in bacterial membrane hydrophilicity. The observed effectiveness of phytochemicals makes them interesting alternatives and/or complementary products to commonly used biocidal products. Cinnamic acid is of particular interest for the control of sessile cells.

Best practice in healthcare environment decontamination.

There is now strong evidence that surface contamination is linked to healthcare-associated infections (HCAIs). Cleaning and disinfection should be sufficient to decrease the microbial bioburden from surfaces in healthcare settings, and, overall, help in decreasing infections. It is, however, not necessarily the case. Evidence suggests that there is a link between educational interventions and a reduction in infections. To improve the overall efficacy and appropriate usage of disinfectants, manufacturers need to engage with the end users in providing clear claim information and product usage instructions. This review provides a clear analysis of the scientific evidence supporting the role of surfaces in HCAIs and the role of education in decreasing such infections. It also examines the debate opposing the use of cleaning versus disinfection in healthcare settings.

Bacillus subtilis vegetative isolate surviving chlorine dioxide exposure: an elusive mechanism of resistance.

AIMS: Oxidizing agents such as chlorine dioxide are widely used microbicides, including for disinfection of medical equipment. We isolated a Bacillus subtilis isolate from a washer-disinfector whose vegetative form demonstrated unique resistance to chlorine dioxide (0·03%) and hydrogen peroxide (7·5%). The aim of this study was to understand the mechanisms of resistance expressed by this isolate. METHODS AND RESULTS: A range of resistance mechanisms were investigated in the B. subtilis isolate and a reference B. subtilis strain (ATCC 6051) to include bacterial cell aggregation, the presence of profuse exopolysaccharide (EPS), and the expression of detoxification enzymes. The basis of resistance of the isolate to high concentrations of oxidizing agents was not linked to the presence of endospores. Although, the presence of EPS, aggregation and expression of detoxification enzymes may play a role in bacterial survival to low concentrations of chlorine dioxide, it is unlikely that the mechanisms helped tested to survive the bactericidal effect of higher oxidizer concentrations. CONCLUSIONS: Overall, the mechanisms conferring resistance to chlorine dioxide and hydrogen peroxide remains elusive. Based on recent advances in the mode of action of oxidizing agents and notably hydrogen peroxide, we postulate that additional efficient intracellular mechanisms may be involved to explain significant resistance to in-use concentrations of commonly used high-level disinfectants. SIGNIFICANCE AND IMPACT OF STUDY: The isolation of a highly resistant vegetative Gram-positive bacterium to a highly reactive oxidizing agent is worrying. Understanding the mechanisms conferring such resistance is essential to effectively control such bacterial isolates. Here, we postulate that there are still mechanisms of bacterial resistance that have not been fully characterized.

Stability and purity of a bacteriophage cocktail preparation for nebulizer delivery.

UNLABELLED: The aim of this study was to determine the stability and purity of a phage cocktail to be delivered by nebulization. A cocktail of three phages active against Pseudomonas aeruginosa isolates from cystic fibrosis patients was developed for a potential nebulized formulation. The individual phages were examined for their retention of activity over time, while the phage cocktail was analysed for bacterial contaminant and endotoxin level according to regulatory requirements for nebulized products. The phage cocktail was nebulized using a Porta-neb nebulizer connected to an Anderson cascade impactor. The three phages retained activity over a period of 180 days storage at room temperature and at 4°C. Nebulized phages were recovered in the lower stages of the cascade impactor indicative of potential delivery deep into the lungs. The phage cocktail met bacterial limits but the endotoxin levels measured with the Limulus amoebocyte lysate (LAL) test remained considerably in excess of acceptable levels even following purification. These findings suggest that nebulization of phage is a viable delivery option; although, there is a need for appropriate depyrogenation strategies to remove bacterial endotoxins from phage-based preparations to meet regulatory requirements. SIGNIFICANCE AND IMPACT OF THE STUDY: With increasing reports of bacterial resistance to antibiotics and the lack of new antibiotics being produced, bacteriophage therapy is becoming an attractive alternative. There has been no published report on the quality assurance of bacteriophage product to date. This is the first study on the quality assurance of a Pseudomonas aeruginosa phage cocktail following pharmacopoeial requirements. The presence of bacterial endotoxin was found to be the key stumbling block for meeting regulatory criteria.

Impact of artificial accelerated ageing of PVC surfaces and surface degradation on disinfectant efficacy.

BACKGROUND: Standardized efficacy surface tests for disinfectants are performed on pristine surfaces. There is a growing interest in understanding the impact of surface ageing on disinfectant activity, owing for example to the increased usage of ultraviolet (UV) radiation and oxidative chemistries for surface decontamination. This acknowledges that general surface 'wear and tear' following UV radiation and oxidative biocide exposure may impact biocidal product efficacy. METHODS: PVC surfaces were aged through thermal and UV-A radiation (340 nm wavelength) following the use of standard ageing surface protocols to simulate natural surface degradation. Surface roughness, contact angle and scanning electron microscopy were performed to evaluate physical changes in PVC surfaces before and after artificial ageing. The efficacy of five pre-impregnated disinfectant wipes were evaluated using the ASTM E2967-15 on stainless-steel (control) and PVC surfaces (aged and non-aged). RESULTS: The type of formulation and the organism tested remained the most significant factors impacting disinfectant efficacy, compared with surface type. Both thermal ageing and UV-A exposure of PVC surfaces clearly showed signs of surface degradation, notably an increase in surface roughness. Physical changes were observed in the roughness of PVC after artificial ageing. A difference in disinfectant efficacy dependent on aged PVC surfaces was observed for some, but not all formulations. CONCLUSION: We showed that surface type and surface ageing can affect biocidal product efficacy, although in a non-predictable manner. More research is needed in this field to ascertain whether surface types and aged surfaces should be used in standardized efficacy testing.

The effect of cationic microbicide exposure against Burkholderia cepacia complex (Bcc); the use of Burkholderia lata strain 383 as a model bacterium.

AIM: The extensive use of microbicides in a wide range of applications has been questioned with regard to their role in the development of bacterial resistance to antimicrobials. This study aims to measure the phenotypic and genotypic changes in Burkholderia lata strain 383 exposed to chlorhexidine gluconate (CHG) and benzalkonium chloride (BZC), two commonly used cationic microbicides. METHODS AND RESULTS: The susceptibility of B. lata strain 383 to CHG and BZC and a range of antibiotics was determined using standardized MIC, MBC and antibiotic susceptibility testing protocols before and after short-term exposure to a low microbicide concentration. Measurements were performed on four separate occasions over a 1-year period. Changes in gene expression were investigated using quantitative real-time PCR. Although the susceptibility profile to CHG and BZC was not altered, a change in antibiotic susceptibility profile was observed for ceftazidime, and for imipenem and ciprofloxacin in 2/4 repeats. An outer membrane protein and ABC transporter were found to be significantly upregulated following treatment with BZC and CHG, respectively. CONCLUSIONS: The comparison of MIC and MBC results following microbicide exposure with baseline data offered a prospective protocol to quantify any change in bacterial susceptibility profile. However, the use of a standardized antibiotic susceptibility protocol with B. lata strain 383 showed some inconsistencies in results between repeats. SIGNIFICANCE AND IMPACT OF THE STUDY: With ever-increasing interest in the impact of microbicides on emerging antimicrobial resistance in bacteria growing, this study demonstrated that comparing susceptibility profile obtained after exposure to microbicides with baseline susceptibility values could play a role in establishing the potential risk of microbicide resistance and cross-resistance development and also in the development of a protocol that allows the prediction of microbicide resistance.

Evaluating the antimicrobial efficacy of long-lasting hand sanitizers on skin.

BACKGROUND: The microbicidal efficacy of hand sanitizer formulations is usually measured through standardized quantitative suspension tests and fingerpad tests; these cannot evaluate long-lasting formulations or are impractical due to biological risks, high cost, or time required for testing. With increased numbers of long-lasting microbicidal activity claims of commercially available hand sanitizers, alternative testing strategies are required. AIM: To explore the use of a standardized ex-vivo pig skin model to reproducibly measure long-lasting efficacy of an alcohol-free hand sanitizer formulation. METHODS: The microbicidal efficacy of an alcohol-free hand sanitizer was tested against Staphylococcus aureus, Escherichia coli and Klebsiella pneumoniae, and the enveloped virus SARS-CoV-2 with quantitative suspension tests (EN13727 and EN14476) with a contact time of 5 min. The product was then tested over a 6 h period using an ex-vivo pig skin model with a modified version of PAS 2424 to simulate the impact of skin abrasion. FINDINGS: Quantitative suspension tests yielded a >5 log10 reduction for all organisms tested within a 5 min contact time. Pig skin tests showed reduced but consistent efficacy at all time points and indicated no significant impact of abrasion on efficacy. CONCLUSION: The use of the ex-vivo pig skin model provides a potentially viable and convenient model system to test long-lasting hand sanitizer formulations, providing a path for sustainable hand sanitizer formulation claims of activity on skin.

Bacterial spore structures and their protective role in biocide resistance.

The structure and chemical composition of bacterial spores differ considerably from those of vegetative cells. These differences largely account for the unique resistance properties of the spore to environmental stresses, including disinfectants and sterilants, resulting in the emergence of spore-forming bacteria such as Clostridium difficile as major hospital pathogens. Although there has been considerable work investigating the mechanisms of action of many sporicidal biocides against Bacillus subtilis spores, there is far less information available for other species and particularly for various Clostridia. This paucity of information represents a major gap in our knowledge given the importance of Clostridia as human pathogens. This review considers the main spore structures, highlighting their relevance to spore resistance properties and detailing their chemical composition, with a particular emphasis on the differences between various spore formers. Such information will be vital for the rational design and development of novel sporicidal chemistries with enhanced activity in the future.

Dry surface biofilms: what you need to know.

Environmental dry surface biofilms are a new type of biofilm found on dry surfaces, that are not visible to the human eye. Dry surface biofilms harbour multidrug-resistant organisms, are resistant to cleaning and disinfection and cannot be detected by wet or dry swabbing, so may play an important role in the persistence of pathogens in the healthcare environment.

Impact of material properties in determining quaternary ammonium compound adsorption and wipe product efficacy against biofilms.

BACKGROUND: Disinfectant wipes containing quaternary ammonium compounds (QACs) are widely used within health care. Viscose remains a popular material for these products, although limited information is available concerning its impact on performance against biofilms when compared with alternatives. AIM: To identify disinfectant wipe materials and surface properties which optimize product performance against biofilms. METHODS: Biofilm eradication performance of two commercial viscose-QAC wipes was determined against Staphylococcus aureus and Acinetobacter baumannii dry surface biofilms (DSBs) using an ASTM E2967-based procedure. Additionally, five materials were impregnated with a commercial liquid formulation containing didecyldimethylammonium chloride (DDAC). Following 24 h of storage, eradication performance and DDAC content of extracted liquid were determined and compared with material properties, including zeta potential, hydrophobicity and surface area. FINDINGS: Under stringent test conditions, eradication of DSBs by commercial products was no greater than equivalent materials impregnated with water. Extract from one viscose-based product contained 89% less DDAC than the impregnation solution, indicating extensive adsorption. Of the other tested materials, viscose performed worst; nearly 70% of DDAC had depleted from material extracts within 24 h. In contrast, DDAC depletion from polypropylene extracts was only 25%, and DSB eradication was >100 times greater than viscose. Biofilm eradication performance against both species correlated with the DDAC content of extracts, which, in turn, correlated with zeta potential and hydrophobicity. CONCLUSION: Biofilm eradication performance of QAC-based wipes was significantly greater when selecting thermoplastic substrates over viscose. However, these materials are non-sustainably sourced and non-biodegradable. This study highlights a need to develop new wipe products that are more effective against biofilms.

Review of decontamination protocols for shared non-critical objects in 35 policies of UK NHS acute care organizations.

BACKGROUND: Decontamination of non-critical objects shared by patients is key in reducing hospital-acquired infections (HAIs), but it is a complex process that needs precise guidance from UK National Health Service (NHS) acute care organizations (ACOs). AIM: To review the indications given by NHS ACOs' policies regarding the decontamination of shared non-critical devices. METHODS: Detailed lists of decontamination protocols for shared non-critical objects were retrieved from cleaning, disinfection and decontamination policies of 35 NHS ACOs. Three parameters were considered for each object: decontamination method, decontamination frequency, and person responsible for decontamination. FINDINGS: In total, 1279 decontamination protocols regarding 283 different shared non-critical objects were retrieved. Of these, 689 (54%) did not indicate the person responsible for decontamination, and only 425 (33%) were complete, giving indications for all three parameters analysed. Only 2.5% (32/1279) of decontamination protocols were complete and identical in two policies. In policies where cleaning represented the major decontamination method, chemical disinfection was rarely mentioned and vice versa. General agreement among policies was found for four main decontamination methods (detergent and water, detergent wipes, disinfectant wipes, and use of disposable items), two decontamination frequencies (between events and daily) and two responsible person designations (nurses and domestic staff). CONCLUSIONS: Decontamination protocol policies for shared non-critical objects had some similarities but did not concur on how each individual object should be decontaminated. The lack of clear indications regarding the person responsible for the decontamination process put at risk the ability of policies to serve as guidance.

Rapid and quantitative automated measurement of bacteriophage activity against cystic fibrosis isolates of Pseudomonas aeruginosa.

INTRODUCTION: Pseudomonas aeruginosa is an opportunistic pathogen and is the main cause of respiratory infection in cystic fibrosis patients. Most strains prevalent within the UK are resistant to two or more antibiotics leading to the search for new therapeutic strategies including the use of bacteriophages. METHODS AND RESULTS: The infectivity of four bacteriophages was increased using an enhancement protocol based on the use of pomegranate rind extract. Their efficacy against 14 Ps. aeruginosa strains was measured using a qualitative streak test and a novel quantitative assay based on the Bioscreen C microbial growth analyzer. Streak test analysis illustrated an increase in the lytic activity of enhanced bacteriophages, whereas Bioscreen analysis showed that both enhanced and unenhanced bacteriophages failed to meet acceptable levels of activity in c. 50% of strains tested. CONCLUSIONS: The quantitative Bioscreen C analyzer showed comparable but not identical results in phage activity and identified significant bacterial re-growth by 20 h postinfection. SIGNIFICANCE AND IMPACT OF THE STUDY: With the resurgence of interest in bacteriophage therapy against infectious bacterial diseases, a rapid high throughput quantitative method for screening phage activity and bacterial resistance is required. The use of the Bioscreen C analyzer meets these criteria and was shown to be more stringent than the traditional streak test.

How dirty is your QWERTY? The risk of healthcare pathogen transmission from computer keyboards.

INTRODUCTION: Healthcare environmental surfaces may be contaminated with micro-organisms that cause healthcare-associated infections (HCAIs). Special attention is paid to near-patient surfaces but sites outside the patient zone receive less attention. This paper presents data on keyboard contamination and the risk of pathogen transmission from keyboards. METHODS: Keyboards from nursing stations in three hospitals and a dental practice were analysed for bacterial contamination. Surfaces were pre-treated to remove planktonic bacteria so that any remaining bacteria were presumed to be associated with biofilm. Bacterial transfer from keyboard keys was studied following wiping with sterile water or sodium hypochlorite. The presence of multi-drug-resistant organisms (MDROs) was sought using selective culture. RESULTS: Moist swabbing did not detect bacteria from any keyboard samples. Use of enrichment broth, however, demonstrated MDROs from most samples. Gram-negative bacteria were recovered from almost half (45%) of the samples, with meticillin-resistant Staphylococcus aureus, vancomycin-resistant enterococcus and MDR Acinetobacter spp. recovered from 72%, 31% and 17% of samples, respectively. Isolates were transferred from 69% of samples after wiping with sterile water, and from 54% of samples after wiping with 1000 ppm sodium hypochlorite. DISCUSSION: While moist swabbing failed to detect bacteria from keyboards, pathogens were recovered using enrichment culture. Use of water- or NaOCl-soaked wipes transferred bacteria from most samples tested. This study implies that hospital keyboards situated outside the patient zone commonly harbour dry surface biofilms (DSBs) that offer a potential reservoir for transferable pathogens. While the role of keyboards in transmission is uncertain, there is a need to pursue effective solutions for eliminating DSBs from keyboards.

Polyhexamethylene biguanide exposure leads to viral aggregation.

AIMS: This study reports the activity of two biguanides against MS2 bacteriophage used as a surrogate virus for nonenveloped mammalian viruses and provides an explanation as to their apparent limited efficacy. METHODS AND RESULTS: When tested in a standard suspension test, two polyhexamethylene biguanides (PHMB), VANTOCIL TG and COSMOCIL CQ, reduced the viability of MS2 by only 1-2 log(10) PFU ml(-1). Exposure time up to 30 min did not affect the activity of the biguanides, although both PHMB were shown to strongly interact with MS2 proteins. CONCLUSIONS: Inactivation kinetics and change in virus hydrophobicity suggested that PHMB induces the formation of viral aggregates. This hypothesis was supported using dynamic light scattering that showed an increase in viral aggregates sizes (up to 500 nm) in a concentration-dependent manner. SIGNIFICANCE AND IMPACT OF THE STUDY: It has been reported that viral aggregation is responsible for virus survival to the biocide exposure. Here, this might be the case, because the virucidal activity of the biguanides was modest and viral aggregation important. The formation of viral aggregates during virus exposure to PHMB was unlikely to overestimate the virucidal potential of the biguanides.