Effects of chronic triclosan exposure upon the antimicrobial susceptibility of 40 ex-situ environmental and human isolates

In vitro response of THP-1 derived macrophages to antimicrobially effective PHMB-coated Ti6Al4V alloy implant material with and without contamination with S. epidermidis and P. aeruginosa

AIM

Periprosthetic joint infections are a devastating complication after arthroplasty, leading to rejection of the prosthesis. The prevention of septic loosening may be possible by an antimicrobial coating of the implant surface. Poly (hexamethylene) biguanide hydrochloride [PHMB] seems to be a suitable antiseptic agent for this purpose since previous studies revealed a low cytotoxicity and a long-lasting microbicidal effect of Ti6Al4V alloy coated with PHMB. To preclude an excessive activation of the immune system, possible inflammatory effects on macrophages upon contact with PHMB-coated surfaces alone and after killing of S. epidermidis and P. aeruginosa are analyzed.

METHODS

THP-1 monocytes were differentiated to M0 macrophages by phorbol 12-myristate 13-acetate and seeded onto Ti6Al4V surfaces coated with various amounts of PHMB. Next to microscopic immunofluorescence analysis of labeled macrophages after adhesion on the coated surface, measurement of intracellular reactive oxygen species and analysis of cytokine secretion at different time points without and with previous bacterial contamination were conducted.

RESULTS

No influence on morphology of macrophages and only slight increases in iROS generation were detected. The cytokine secretion pattern depends on the surface treatment procedure and the amount of adsorbed PHMB. The PHMB coating resulted in a high reduction of viable bacteria, resulting in no significant differences in cytokine secretion as reaction to coated surfaces with and without bacterial burden.

CONCLUSION

Ti6Al4V specimens after alkaline treatment followed by coating with 5-7 μg PHMB and specimens treated with H2O2 before PHMB-coating (4 μg) had the smallest influence on the macrophage phienotype and thus are considered as the surface with the best cytocompatibility to macrophages tested in the present study.

Assessing the Risk of Resistance to Cationic Biocides incorporating Realism-based and Biophysical Approaches

The control of microorganisms is a key objective in disease prevention and in medical, industrial, domestic, and food-production environments. Whilst the effectiveness of biocides in these contexts is well-evidenced, debate continues about the resistance risks associated with their use. This has driven an increased regulatory burden, which in turn could result in a reduction of both the deployment of current biocides and the development of new compounds and formulas. Efforts to balance risk and benefit are therefore of critical importance and should be underpinned by realistic methods and a multi-disciplinary approach, and through objective and critical analyses of the literature. The current literature on this topic can be difficult to navigate. Much of the evidence for potential issues of resistance generation by biocides is based on either correlation analysis of isolated bacteria, where reports of treatment failure are generally uncommon, or laboratory studies that do not necessarily represent real biocide applications. This is complicated by inconsistencies in the definition of the term resistance. Similar uncertainties also apply to cross-resistance between biocides and antibiotics. Risk assessment studies that can better inform practice are required. The resulting knowledge can be utilised by multiple stakeholders including those tasked with new product development, regulatory authorities, clinical practitioners, and the public. This review considers current evidence for resistance and cross-resistance and outlines efforts to increase realism in risk assessment. This is done in the background of the discussion of the mode of application of biocides and the demonstrable benefits as well as the potential risks.

Auto-Disinfectant Acrylic Paints Functionalised with Triclosan and Isoborneol-Antibacterial Assessment

Environmental surface contamination with microorganisms is a serious concern worldwide. Triclosan and isoborneol present good antimicrobial activity. Their immobilisation to paint substrates allows for development of a material that stays effective over a longer time. In this work, we disclosed the preliminary studies to evaluate the antimicrobial activity of the active molecule after being functionalised with isocyanates for further immobilisation on the paint substrate. Overall, the newly developed non-release antimicrobial coating provides an effective way of preventing the spread of diseases and has been proven to inhibit bacterial growth and with a considerable antimicrobial activity towards S. aureus, E. coli, and K. variicola at the tested concentrations.

Antibiotic-resistant Escherichia coli and Klebsiella spp. in greywater reuse systems and pond water used for agricultural irrigation in the West Bank, Palestinian Territories

Treating and reusing greywater for agricultural irrigation is becoming increasingly prevalent in water-scarce regions such as the Middle East. However, the potential for antibiotic-resistant bacteria to be introduced into food systems or the environment via greywater reuse is a potential area of concern. It is known that off-grid treated greywater often has elevated levels of bacteria, however, little is known regarding the prevalence of antibiotic-resistant bacteria in this water source. To address this knowledge gap, samples (n = 61) of off-grid, household greywater (influent), treated greywater effluent, and irrigation pond water were collected between October 2017 and June 2018 from four farms in the West Bank, Palestinian Territories. Samples were tested for pH, turbidity, dissolved oxygen, electrical conductivity, and oxidation reduction potential. Standard membrane filtration was used to enumerate presumptive Escherichia coli, and isolates (n = 88) were purified, confirmed using 16S rRNA sequencing, and subjected to antimicrobial susceptibility testing using microbroth dilution. The majority of influent (76.5%) and effluent (70.6%) samples had detectable presumptive E. coli. Interestingly, the majority of the isolates were confirmed as Klebsiella sp. (n = 37), followed by E. coli (n = 32), and the remainder were classified as other Enterobacteriaceae (n = 19). A higher percentage of effluent isolates were fully susceptible to all tested antibiotics when compared to influent isolates (28.6% vs 18.6%). Resistance was most commonly observed against ampicillin (69.3% of all isolates), trimethoprim-sulfamethoxazole (11.4%), tetracycline (9.1%), and cefazolin (7.9%), and 7.9% of isolates were observed to be multidrug-resistant. While most water quality parameters were within Israeli and Palestinian wastewater reuse requirements, E. coli levels in effluent violated available standards. These findings suggest that, despite observed decreases in bacteria and an overall decrease in isolates expressing antibiotic resistance from influent to effluent, off-grid greywater treatment systems are still a potential source of both susceptible and antibiotic-resistant bacteria in the agricultural environment.

Synergistic and antagonistic interactions of triclosan with various antibiotics in bacteria

Triclosan (TCS), a well-studied antimicrobial compound and an environmental pollutant, is present in many household products. A systematic survey of TCS-antibiotic-bacteria interactions is lacking. We wish to understand the origin of such interactions by testing 16 phylogenetically well-characterized bacteria for their sensitivities to 6 different classes of antibiotics with or without the presence of TCS. Our results show that TCS interacts synergistically with some antibiotics against some Bacilli species. TCS could also interact antagonistically with other antibiotics against certain bacteria, including pathogens such as Pseudomonas aeruginosa and Stenotrophomonas maltophilia. Antagonism between drugs often coincided with the concomitant enhanced removal of Ethidium bromide (EtBr) from the cells. Enterococcus faecalis shows a unique response to TCS. High levels of TCS inhibits E. faecalis. Cells survive at lower TCS concentrations, and these cells can remove EtBr more readily than unexposed cells. At even lower TCS concentration, cell-growth is inhibited again, causing the culture to exhibit a unique extra inhibition zone around the TCS-disk. The TCS-antibiotic-bacteria interaction profiles of some bacteria do not follow their bacterial phylogenetic relations. This suggests that such interactions may be related to horizontal gene transfer among different bacteria.

Associations between sensitivity to antibiotics, disinfectants and heavy metals in natural, clinical and laboratory isolates of Escherichia coli

Bacteria in nature often encounter non-antibiotic antibacterials (NAAs), such as disinfectants and heavy metals, and they can evolve resistance via mechanisms that are also involved in antibiotic resistance. Understanding whether susceptibility to different types of antibacterials is non-randomly associated across natural and clinical bacteria is therefore important for predicting the spread of resistance, yet there is no consensus about the extent of such associations or underlying mechanisms. We tested for associations between susceptibility phenotypes of 93 natural and clinical Escherichia coli isolates to various NAAs and antibiotics. Across all compound combinations, we detected a small number of non-random associations, including a trio of positive associations among chloramphenicol, triclosan and benzalkonium chloride. We investigated genetic mechanisms that can explain such associations using genomic information, genetic knockouts and experimental evolution. This revealed some mutations that are selected for by experimental exposure to one compound and confer cross-resistance to other compounds. Surprisingly, these interactions were asymmetric: selection for chloramphenicol resistance conferred cross-resistance to triclosan and benzalkonium chloride, but selection for triclosan resistance did not confer cross-resistance to other compounds. These results identify genetic changes involved in variable cross-resistance across antibiotics and NAAs, potentially contributing to associations in natural and clinical bacteria.

Triclosan exposure induces varying extent of reversible antimicrobial resistance in Aeromonas hydrophila and Edwardsiella tarda

Triclosan (TCS) is a biocide commonly used in household and personal care items to prevent the microbial growth and is currently considered as an emerging pollutant. It has a ubiquitous distribution which can substantially contribute towards antimicrobial resistance. The present study was designed to evaluate the effect of different concentrations of TCS exposure on the antibiotic sensitivity of aquatic bacteria. Aeromonas hydrophila ATCC^® 49140^™ and Edwardsiella tarda ATCC^® 15947^™ exposed to TCS for short (30 min) and long duration (serial passages). The agar-disc diffusion assay during the serial passages of TCS exposure and subsequent exposure withdrawal showed clinically insignificant changes in the zone of inhibition for six selected antibiotics in both bacterial strains at all exposure concentrations. Four folds concentration-dependent increase in the minimum inhibitory concentrations (MICs) of TCS was observed in both the strains following TCS exposure. Similarly, a concentration-dependent increase in the MICs of oxytetracycline (OTC) up to 4 folds in A. hydrophila, and up to 8 folds in E. tarda, was also documented during the TCS exposure. In all the cases, withdrawal of TCS exposure effectively reduced the MICs of TCS and OTC in blank passages suggesting a decline in acquired resistance. The frequencies of mutation during 30 min TCS exposure for E. tarda and A. hydrophila ranged between >10^-6 and 10^-7 levels. Nevertheless, the TCS exposure did not cause any detectable mutation on the fabV gene of A. hydrophila indicating that the TCS may elicit phenotypic adaptation or other resistance mechanism. Although the reduction in MICs due to exposure withdrawal did not restore the bacterial susceptibility up to the initial level, the study proved that the reduced TCS use could significantly help reduce the antimicrobial-resistance and cross-resistance in pathogenic bacteria.

Effect of a Glyphosate-Containing Herbicide on Escherichia coli and Salmonella Ser. Typhimurium in an In Vitro Rumen Simulation System

Glyphosate (N-(phosphonomethyl)glycine) is the most-used herbicide worldwide. Many studies in the past have shown that residues of the herbicide can be found in many cultivated plants, including those used as livestock feed. Sensitivity to glyphosate varies with bacteria, particularly those residing in the intestine, where microbiota is exposed to glyphosate residues. Therefore, less susceptible pathogenic isolates could have a distinct advantage compared to more sensitive commensal isolates, probably leading to dysbiosis. To determine whether the ruminal growth and survival of pathogenic Escherichia coli or Salmonella serovar Typhimurium are higher when glyphosate residues are present in the feed, an in vitro fermentation trial with a "Rumen Simulation System" (RUSITEC) and a glyphosate-containing commercial formulation was performed. Colony forming units of E. coli and Salmonella ser. Typhimurium decreased steadily in all fermenters, regardless of the herbicide application. Minimum inhibitory concentrations of the studied Salmonella and E. coli strains did not change, and antibiotic susceptibility varied only slightly but independent of the glyphosate application. Overall, application of the glyphosate-containing formulation in a worst-case concentration of 10 mg/L neither increased the abundance for the tested E. coli and Salmonella strain in the in vitro fermentation system, nor promoted resistance to glyphosate or antibiotics.

Minimum Inhibitory Concentration of Glyphosate and of a Glyphosate-Containing Herbicide Formulation for Escherichia coli Isolates - Differences Between Pathogenicand Non-pathogenic Isolates and Between Host Species

Glyphosate is the most extensively used herbicide in the world. However, concerns regarding its safety, side effects, and impact on other organisms have increased in recent years. This is the first study to analyze a large set of recent and historical Escherichia coli isolates varying in pathogenicity and beta-lactam resistance from different host species for their susceptibility to glyphosate isopropylamine salt (IPA), the active ingredient of the herbicide, and to a complete glyphosate-containing formulation (Roundup LB Plus). For this, minimum inhibitory concentrations (MIC) were determined for 238 E. coli isolates by broth microdilution in Mueller Hinton I media followed by the statistical analyses using Mann-Whitney-U test, multivariable analysis of variance (ANOVA) and a multivariable proportional-odds ordinal regression model. While the overall MIC distribution was narrow and lacked a highly resistant sub-population for both substances, statistical analyses revealed small but significant associations between glyphosate resistance levels and different factors tested. Mean MIC values for the entire dataset showed a higher level of resistance to the complete glyphosate-containing formulation (40 mg/ml IPA) than to pure glyphosate (10 mg/ml IPA) in E. coli. Isolates that originated from poultry had significantly higher MIC values for both pure glyphosate and the complete formulation. Pathogenic and non-extended-spectrum beta-lactamase (non-ESBL) E. coli isolates each showed significantly higher MIC values compared to commensals and ESBL-producing E. coli in pure glyphosate, but not in the complete formulation. Recently sampled isolates showed statistically higher MICs than the isolates of the historic standard E. coli collection of reference in pure glyphosate, when tested by nonparametric Mann-Whitney-U test, but not in the multivariable model. Further investigations are necessary to confirm whether these associations have a casual relationship with the glyphosate use or are the consequence of co-selection due to the increased application rates of antibiotics, heavy metals or other biocides. A possible accumulation of pathogenic bacteria in livestock animals fed with glyphosate-containing feed should also be considered.

Antimicrobial Chemicals Associate with Microbial Function and Antibiotic Resistance Indoors

The ubiquitous use of antimicrobial chemicals may have undesired consequences, particularly on microbes in buildings. This study shows that the taxonomy and function of microbes in indoor dust are strongly associated with antimicrobial chemicals—more so than any other feature of the buildings. Moreover, we identified links between antimicrobial chemical concentrations in dust and culturable bacteria that are cross-resistant to three clinically relevant antibiotics. These findings suggest that humans may be influencing the microbial species and genes that are found indoors through the addition and removal of particular antimicrobial chemicals.

Humans purposefully and inadvertently introduce antimicrobial chemicals into buildings, resulting in widespread compounds, including triclosan, triclocarban, and parabens, in indoor dust. Meanwhile, drug-resistant infections continue to increase, raising concerns that buildings function as reservoirs of, or even select for, resistant microorganisms. Support for these hypotheses is limited largely since data describing relationships between antimicrobials and indoor microbial communities are scant. We combined liquid chromatography-isotope dilution tandem mass spectrometry with metagenomic shotgun sequencing of dust collected from athletic facilities to characterize relationships between indoor antimicrobial chemicals and microbial communities. Elevated levels of triclosan and triclocarban, but not parabens, were associated with distinct indoor microbiomes. Dust of high triclosan content contained increased Gram-positive species with diverse drug resistance capabilities, whose pangenomes were enriched for genes encoding osmotic stress responses, efflux pump regulation, lipid metabolism, and material transport across cell membranes; such triclosan-associated functional shifts have been documented in laboratory cultures but not yet from buildings. Antibiotic-resistant bacterial isolates were cultured from all but one facility, and resistance often increased in buildings with very high triclosan levels, suggesting links between human encounters with viable drug-resistant bacteria and local biocide conditions. This characterization uncovers complex relationships between antimicrobials and indoor microbiomes: some chemicals elicit effects, whereas others may not, and no single functional or resistance factor explained chemical-microbe associations. These results suggest that anthropogenic chemicals impact microbial systems in or around buildings and their occupants, highlighting an emergent need to identify the most important indoor, outdoor, and host-associated sources of antimicrobial chemical-resistome interactions.

IMPORTANCE The ubiquitous use of antimicrobial chemicals may have undesired consequences, particularly on microbes in buildings. This study shows that the taxonomy and function of microbes in indoor dust are strongly associated with antimicrobial chemicals—more so than any other feature of the buildings. Moreover, we identified links between antimicrobial chemical concentrations in dust and culturable bacteria that are cross-resistant to three clinically relevant antibiotics. These findings suggest that humans may be influencing the microbial species and genes that are found indoors through the addition and removal of particular antimicrobial chemicals.

Multiple drug resistance and biocide resistance in Escherichia coli environmental isolates from hospital and household settings

Background

Antibiotic resistance of environmental Escherichia coli in hospitals could be increased due to extensive use of biocides resulting in serious infections. In this study, the prevalence of antibiotic resistance of environmental isolates of E. coli from hospitals and household settings were evaluated and compared. In addition, the association between biocide minimum inhibitory concentration (MIC) and multiple drug resistance (MDR) was investigated.

Methods

Environmental samples were collected from different homes and hospitals in Amman, Jordan. The isolates were identified phenotypically and by PCR. Antibiotic susceptibility tests and MIC of selected biocides were performed on the isolates. Screening for blaCTX-M group 1 was also performed.

Results

Of 21 E. coli strains isolated, 47.6% were MDR and 67.9% were phenotypically identified as extended spectrum beta-lactamase (ESBL) producers. The occurrence of these ESBL isolates was comparable between household and hospital settings (P > 0.05). The MIC values of the biocides tested against all isolates were well below the in-use concentration of biocides. Moreover, the MICs of biocides were comparable between isolates from households and those from hospitals (P > 0.05). No association was found between MDR and biocide MIC (P > 0.05). Most of ESBL isolates harboured blaCTX-M 1.

Conclusions

The extensive use of biocides in hospitals is not associated with MDR nor does it affect the MIC of biocides against E.coli.

A novel method to detect bacterial resistance to disinfectants

In clinical practice, the important hygienic prevention of bacterial pathogen spread is disinfection of potentially contaminated area. Benzalkonium bromide and chlorhexidine acetate are commonly used disinfectants with a broad spectrum of anti-microbial effect. It is vital to inhibit the spread of pathogen in hospital. However, a large number of pathogens with the decreased antiseptic susceptibility have been isolated from clinical samples which showed an increased minimal inhibitory concentration (MIC) against those antiseptics. These resistant pathogens are the major causes for nosocomial cross-infections in hospital. The present study demonstrated the utility of Oxford plate assay system in determining the potential disinfectant resistance of bacteria. The microbiological assay is based on the inhibitory effect of tested disinfectants upon the strains of Staphylococcus aureus and Escherichia coli. Statistical analysis of the bioassay results indicated the linear correlation (r = 0.87–0.99, P < 0.01) between the diameter of growth inhibition zone and the log dosage of the tested disinfectants. Moreover, comparison of inhibitory efficacy of benzalkonium bromide upon 29 S. aureus strains isolated from clinical samples by both Oxford plate method and broth dilution method showed that the diameter of growth inhibition zone has significantly negative correlation with the minimal inhibitory concentration (MIC) (r = −0.574, P < 0.001). These results suggest that the Oxford plate is a simple and time-saving method in detecting potential clinical disinfectant resistance and its usefulness for routine surveillance of pathogenic resistance to disinfectants warrants further investigation.

Variable Effects of Exposure to Formulated Microbicides on Antibiotic Susceptibility in Firmicutes and Proteobacteria

Microbicides are broad-spectrum antimicrobial agents that generally interact with multiple pharmacological targets. While they are widely deployed in disinfectant, antiseptic, and preservative formulations, data relating to their potential to select for microbicide or antibiotic resistance have been generated mainly by testing the compounds in much simpler aqueous solutions. In the current investigation, antibiotic susceptibility was determined for bacteria that had previously exhibited decreased microbicide susceptibility following repeated exposure to microbicides either in formulation with sequestrants and surfactants or in simple aqueous solution. Statistically significant increases in antibiotic susceptibility occurred for 12% of bacteria after exposure to microbicides in formulation and 20% of bacteria after exposure to microbicides in aqueous solutions, while 22% became significantly less susceptible to the antibiotics, regardless of formulation. Of the combinations of a bacterium and an antibiotic for which British Society for Antimicrobial Chemotherapy breakpoints are available, none became resistant. Linear modeling taking into account phylogeny, microbicide, antibiotic, and formulation identified small but significant effects of formulation that varied depending on the bacterium and microbicide. Adaptation to formulated benzalkonium chloride in particular was more likely to increase antibiotic susceptibility than adaptation to the simple aqueous solution. In conclusion, bacterial adaptation through repeated microbicide exposure was associated with both increases and decreases in antibiotic susceptibility. Formulation of the microbicide to which the bacteria had previously adapted had an identifiable effect on antibiotic susceptibility, but it effect was typically small relative to the differences observed among microbicides. Susceptibility changes resulting in resistance were not observed.

IMPORTANCE

The safety of certain microbicide applications has been questioned due to the possibility that microbicide exposure could select for microbicide and antibiotic resistance. Evidence that this may happen is based mainly on in vitro experiments where bacteria have been exposed to microbicides in aqueous solution. Microbicides are, however, normally deployed in products formulated with surfactants, sequestrants, and other compounds. While this may influence the frequency and extent of susceptibility changes, few studies reported in the literature have assessed this. In the current investigation, therefore, we have investigated changes in antibiotic susceptibility in bacteria which exhibited decreased microbicide susceptibility following repeated exposure to microbicides in simple aqueous solutions and in formulation. We report that the microbicide formulation had an identifiable effect on antibiotic susceptibility, but it was typically small relative to the differences observed among microbicides. We did not observe susceptibility changes resulting in resistance.

Occurrence of Stenotrophomonas maltophilia in agricultural soils and antibiotic resistance properties

The occurrence of Stenotrophomonas maltophilia was monitored in organic amendments and agricultural soils from various sites in France and Tunisia. S. maltophilia was detected in horse and bovine manures, and its abundance ranged from 0.294 (±0.509) × 10(3) to 880 (±33.4) × 10(3) CFU (g drywt)(-1) of sample. S. maltophilia was recovered from most tested soil samples (104/124). Its abundance varied from 0.33 (±0.52) to 414 (±50) × 10(3) CFU (g drywt)(-1) of soil and was not related to soil characteristics. Antibiotic resistance properties of a set of environmental strains were compared to a clinical set, and revealed a high diversity of antibiotic resistance profiles, given both the numbers of resistance and the phenotypes. Manure strains showed resistance phenotypes, with most of the strains resisting between 7 and 9 antibiotics. While French soil strains were sensitive to most antibiotics tested, some Tunisian strains displayed resistance phenotypes close to those of clinical French strains. Screening for metal resistance among 66 soil strains showed a positive relationship between antibiotic and metal resistance. However, the prevalence of antibiotic resistance phenotypes in the studied sites was not related to the metal content in soil samples.

Co-Selection of Resistance to Antibiotics, Biocides and Heavy Metals, and Its Relevance to Foodborne Pathogens

Concerns have been raised in recent years regarding co-selection for antibiotic resistance among bacteria exposed to biocides used as disinfectants, antiseptics and preservatives, and to heavy metals (particularly copper and zinc) used as growth promoters and therapeutic agents for some livestock species. There is indeed experimental and observational evidence that exposure to these non-antibiotic antimicrobial agents can induce or select for bacterial adaptations that result in decreased susceptibility to one or more antibiotics. This may occur via cellular mechanisms that are protective across multiple classes of antimicrobial agents or by selection of genetic determinants for resistance to non-antibiotic agents that are linked to genes for antibiotic resistance. There may also be relevant effects of these antimicrobial agents on bacterial community structure and via non-specific mechanisms such as mobilization of genetic elements or mutagenesis. Notably, some co-selective adaptations have adverse effects on fitness in the absence of a continued selective pressure. The present review examines the evidence for the significance of these phenomena, particularly in respect of bacterial zoonotic agents that commonly occur in livestock and that may be transmitted, directly or via the food chain, to human populations.

Effects of Formulation on Microbicide Potency and Mitigation of the Development of Bacterial Insusceptibility

Risk assessments of the potential for microbicides to select for reduced bacterial susceptibility have been based largely on data generated through the exposure of bacteria to microbicides in aqueous solution. Since microbicides are normally formulated with multiple excipients, we have investigated the effect of formulation on antimicrobial activity and the induction of bacterial insusceptibility. We tested 8 species of bacteria (7 genera) before and after repeated exposure (14 passages), using a previously validated gradient plating system, for their susceptibilities to the microbicides benzalkonium chloride, benzisothiozolinone, chlorhexidine, didecyldimethyl ammonium chloride, DMDM-hydantoin, polyhexamethylene biguanide, thymol, and triclosan in aqueous solution (nonformulated) and in formulation with excipients often deployed in consumer products. Susceptibilities were also assessed following an additional 14 passages without microbicide to determine the stability of any susceptibility changes. MICs and minimum bactericidal concentrations (MBC) were on average 11-fold lower for formulated microbicides than for nonformulated microbicides. After exposure to the antimicrobial compounds, of 72 combinations of microbicide and bacterium there were 19≥4-fold (mean, 8-fold) increases in MIC for nonformulated and 8≥4-fold (mean, 2-fold) increases in MIC for formulated microbicides. Furthermore, there were 20≥4-fold increases in MBC (mean, 8-fold) for nonformulated and 10≥4-fold (mean, 2-fold) increases in MBC for formulated microbicides. Susceptibility decreases fully or partially reverted back to preexposure values for 49% of MICs and 72% of MBCs after further passage. In summary, formulated microbicides exhibited greater antibacterial potency than unformulated actives and susceptibility decreases after repeated exposure were lower in frequency and extent.

Altered Competitive Fitness, Antimicrobial Susceptibility, and Cellular Morphology in a Triclosan-Induced Small-Colony Variant of Staphylococcus aureus

Staphylococcus aureus can produce small-colony variants (SCVs) that express various phenotypes. While their significance is unclear, SCV propagation may be influenced by relative fitness, antimicrobial susceptibility, and the underlying mechanism. We have investigated triclosan-induced generation of SCVs in six S. aureus strains, including methicillin-resistant S. aureus (MRSA). Parent strains (P0) were repeatedly passaged on concentration gradients of triclosan using a solid-state exposure system to generate P10. P10 was subsequently passaged without triclosan to generate X10. Susceptibility to triclosan and 7 antibiotics was assessed at all stages. For S. aureus ATCC 6538, SCVs were further characterized by determining microbicide susceptibility and competitive fitness. Cellular morphology was examined using electron microscopy, and protein expression was evaluated through proteomics. Triclosan susceptibility in all SCVs (which could be generated from 4/6 strains) was markedly decreased, while antibiotic susceptibility was significantly increased in the majority of cases. An SCV of S. aureus ATCC 6538 exhibited significantly increased susceptibility to all tested microbicides. Cross-wall formation was impaired in this bacterium, while expression of FabI, a target of triclosan, and IsaA, a lytic transglycosylase involved in cell division, was increased. The P10 SCV was 49% less fit than P0. In summary, triclosan exposure of S. aureus produced SCVs in 4/6 test bacteria, with decreased triclosan susceptibility but with generally increased antibiotic susceptibility. An SCV derived from S. aureus ATCC 6538 showed reduced competitive fitness, potentially due to impaired cell division. In this SCV, increased FabI expression could account for reduced triclosan susceptibility, while IsaA may be upregulated in response to cell division defects.

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.

Antibiotic-resistant bacteria: a challenge for the food industry

Antibiotic-resistant bacteria were first described in the 1940s, but whereas new antibiotics were being discovered at a steady rate, the consequences of this phenomenon were slow to be appreciated. At present, the paucity of new antimicrobials coming into the market has led to the problem of antibiotic resistance fast escalating into a global health crisis. Although the selective pressure exerted by the use of antibiotics (particularly overuse or misuse) has been deemed the major factor in the emergence of bacterial resistance to these antimicrobials, concerns about the role of the food industry have been growing in recent years and have been raised at both national and international levels. The selective pressure exerted by the use of antibiotics (primary production) and biocides (e.g., disinfectants, food and feed preservatives, or decontaminants) is the main driving force behind the selection and spread of antimicrobial resistance throughout the food chain. Genetically modified (GM) crops with antibiotic resistance marker genes, microorganisms added intentionally to the food chain (probiotic or technological) with potentially transferable antimicrobial resistance genes, and food processing technologies used at sub-lethal doses (e.g., alternative non-thermal treatments) are also issues for concern. This paper presents the main trends in antibiotic resistance and antibiotic development in recent decades, as well as their economic and health consequences, current knowledge concerning the generation, dissemination, and mechanisms of antibacterial resistance, progress to date on the possible routes for emergence of resistance throughout the food chain and the role of foods as a vehicle for antibiotic-resistant bacteria. The main approaches to prevention and control of the development, selection, and spread of antibacterial resistance in the food industry are also addressed.

Antibacterial-coated suture in reducing surgical site infection in breast surgery: a prospective study

Background. To reduce the incidence of microbial colonization of suture material, Triclosan- (TC-)coated suture materials have been developed. The aim of this study was to assess the incidence of suture-related complications (SRC) in breast surgery with and without the use of TC-coated sutures. Methods. We performed a study on two consecutive periods: 92 patients underwent breast surgery with conventional sutures (Group 1) and 98 with TC-coated sutures (Group 2). We performed subgroups analyses and developed a model to predict SRC in Group 1 and tested its clinical efficacy in Group 2 using a nomogram-based approach. Results. The SRC rates were 13% in Group 1 and 8% in Group 2. We found that some subgroups may benefit from TC-coated sutures. The discrimination obtained from a logistic regression model developed in Group 1 and based on multifocality, age and axillary lymphadenectomy was 0.88 (95% CI 0.77-0.95) (P < 10(-4)). There was a significant difference in Group 2 between predicted probabilities and observed percentages (P < 10(-5)). The predicted and observed proportions of complications in the high-risk group were 38% and 13%, respectively. Conclusion. This study used individual predictions of SRC and showed that using TC-coated suture may prevent SRC. This was particularly significant in high-risk patients.

The frequency of antibiotic-resistant bacteria in homes differing in their use of surface antibacterial agents

Antibacterial agents are common in household cleaning and personal care products, but their long-range impacts on commensal and pathogenic household bacteria are largely unknown. In a one-time survey of 38 households from Boston, MA [19] and Cincinnati, OH [18], 13 kitchen and bathroom sites were sampled for total aerobic bacteria and screened for gram phenotype and susceptibility to six antibiotic drug families. The overall bacterial titers of both user (2 or more antibacterial cleaning or personal care products) and non-user (0 or 1 product) rooms were similar with sponges and sink drains consistently showing the highest overall titers and relatively high titers of antibiotic-resistant bacteria. The mean frequency of resistant bacteria ranged from ≤20 % to as high as 45 % and multi-drug resistance was common. However, no significant differences were noted between biocide users and non-users. The frequency of pathogen recovery was similar in both user and non-user groups.

Attenuated virulence and biofilm formation in Staphylococcus aureus following sublethal exposure to triclosan

Subeffective exposure of Staphylococcus aureus to the biocide triclosan can reportedly induce a small-colony variant (SCV) phenotype. S. aureus SCVs are characterized by low growth rates, reduced pigmentation, and lowered antimicrobial susceptibility. While they may exhibit enhanced intracellular survival, there are conflicting reports regarding their pathogenicity. The current study reports the characteristics of an SCV-like strain of S. aureus created by repeated passage on sublethal triclosan concentrations. S. aureus ATCC 6538 (the passage 0 [P0] strain) was serially exposed 10 times to concentration gradients of triclosan to generate strain P10. This strain was then further passaged 10 times on triclosan-free medium (designated strain ×10). The MICs and minimum bactericidal concentrations of triclosan for P0, P10, and ×10 were determined, and growth rates in biofilm and planktonic cultures were measured. Hemolysin, DNase, and coagulase activities were measured, and virulence was determined using a Galleria mellonella pathogenicity model. Strain P10 exhibited decreased susceptibility to triclosan and characteristics of an SCV phenotype, including a considerably reduced growth rate and the formation of pinpoint colonies. However, this strain also had delayed coagulase production, had impaired hemolysis (P < 0.01), was defective in biofilm formation and DNase activity, and displayed significantly attenuated virulence. Colony size, hemolysis, coagulase activity, and virulence were only partially restored in strain ×10, whereas the planktonic growth rate was fully restored. However, ×10 was at least as defective in biofilm formation and DNase production as P10. These data suggest that although repeated exposure to triclosan may result in an SCV-like phenotype, this is not necessarily associated with increased virulence and adapted bacteria may exhibit other functional deficiencies.

Stenotrophomonas maltophilia: an emerging global opportunistic pathogen

Stenotrophomonas maltophilia is an emerging multidrug-resistant global opportunistic pathogen. The increasing incidence of nosocomial and community-acquired S. maltophilia infections is of particular concern for immunocompromised individuals, as this bacterial pathogen is associated with a significant fatality/case ratio. S. maltophilia is an environmental bacterium found in aqueous habitats, including plant rhizospheres, animals, foods, and water sources. Infections of S. maltophilia can occur in a range of organs and tissues; the organism is commonly found in respiratory tract infections. This review summarizes the current literature and presents S. maltophilia as an organism with various molecular mechanisms used for colonization and infection. S. maltophilia can be recovered from polymicrobial infections, most notably from the respiratory tract of cystic fibrosis patients, as a cocolonizer with Pseudomonas aeruginosa. Recent evidence of cell-cell communication between these pathogens has implications for the development of novel pharmacological therapies. Animal models of S. maltophilia infection have provided useful information about the type of host immune response induced by this opportunistic pathogen. Current and emerging treatments for patients infected with S. maltophilia are discussed.

Antimicrobial sutures and prevention of surgical site infection: assessment of the safety of the antiseptic triclosan

This article is based on a second Hygienist Panel meeting held in London on 16-17 June 2010. The Panel discussed the current use of antimicrobials and care bundles in the prevention of surgical site infection; the need to comply with good antibiotic stewardship, to reduce the risk of antibiotic-resistant and emergent organisms; and the need to revisit the use of antiseptics. The discussion was driven by concerns of the use of triclosan, which had been raised by a publication from the Scientific Committee on Consumer Products of the Directorate General for Health and Consumers, European Commission. Uncertainties that excessive use of triclosan for preservation and in cosmetics could select naturally resistant environmental organisms or induce reduced triclosan-susceptibility or antibiotic resistance were considered. It was concluded that the uses of triclosan with demonstrable health benefits, as in some medical applications (such as antimicrobial sutures), need to be distinguished from those where there is no proven benefit, such as its use in certain consumer products. The addition of triclosan to a product must be substantiated in any claim of preventive or therapeutic health benefit. Triclosan is the most widely studied biocide and this same level of information should be available for other topically used antimicrobials, which are widely used in surgical practice and chronic wound care.

Triclosan - an update

The discovery in 1998 that triclosan has a site-specific action in the bacterial cell as an inhibitor of NADH- or NADPH-dependent enoyl-acyl carrier protein reductase led to a lively debate in the scientific press. The thesis of this debate was that such a mode of action may allow triclosan to induce resistance and cross-resistance in bacterial cells. The debate last saw review in 2004, and this paper aims at updating our knowledge in this area, given recent research on the topic.

Characterization of triclosan-resistant mutants reveals multiple antimicrobial resistance mechanisms in Rhodospirillum rubrum S1H

Antimicrobial resistance mechanisms were identified in 11 spontaneous high- and low-level triclosan resistance (Tcs(r)) mutants of Rhodospirillum rubrum S1H by genotyping complemented with transcriptional analyses, antibiotic resistance screening, and membrane permeability analyses. High-end Tcs(r) (MIC = 8 mg/liter) was the result of a FabI1(G98V) mutation. This point mutation led to an even higher level of Tcs(r) (MIC > or = 16 mg/liter) in combination with constitutive upregulation of mexB and mexF efflux pump homologs. Hence, a mechanistic synergy of constitutive efflux pump expression and a FabI1 point mutation could prevent TCS-induced cell permeabilization, which was shown to occur between 4 and 8 mg/liter TCS in the R. rubrum S1H parent strain. Low-level Tcs(r) mutants constitutively upregulated the emrAB, mexAB, and/or mexF homolog. The mutants that overexpressed emrAB also derepressed the micropollutant-upregulated factors mufA1 and mufM. In some cases, low-level Tcs(r) decreased innate resistance to ampicillin and tetracycline, while in others, a triclosan-induced antibiotic cross-resistance was shown for chloramphenicol and carbenicillin. This study showed that the TCS resistance degree is dependent of the initial exposure concentration in Rhodospirillum rubrum S1H and that similar resistance degrees can be the result of different defense mechanisms, which all have distinct antibiotic cross-resistance profiles.

Sensitizing potential of triclosan and triclosan-based skin care products in patients with chronic eczema

Triclosan is a lypophilic chlorophenol biocide with broad-spectrum antibacterial and antifungal activity. Triclosan-based topical products have been shown to be tolerated and beneficial in atopic dermatitis. The aim of this study was to evaluate the sensitizing potential of triclosan and triclosan-based creams in patients affected by eczematous dermatitis. Two hundred and seventy-five patients affected by chronic eczema (allergic contact dermatitis, irritant contact dermatitis, atopic eczema, nummular eczema, stasis dermatitis) were patch tested with standard patch test series as well as triclosan and triclosan-based products. Standard patch test series resulted positive in 164 patients (61%), with nickel sulfate, house dust mites, fragrance mix, propolis, thimerosal, myroxylon pereira, potassium dichromate, wool alcohols, and p-phenylenediamine the most common sensitizing haptens. Only two patients developed positive reactions to triclosan (0.7%) and four (1.4%) to triclosan-based products. The present study's results confirm that triclosan is well tolerated and has a very low sensitizing potential even in high-risk patients affected by eczema.

Toxicity of triclosan, penconazole and metalaxyl on Caulobacter crescentus and a freshwater microbial community as assessed by flow cytometry

Biocides are widely used for domestic hygiene, agricultural and industrial applications. Their widespread use has resulted in their introduction into the environment and raised concerns about potential deleterious effects on aquatic ecosystems. In this study, the toxicity of the biocides triclosan, penconazole and metalaxyl were evaluated with the freshwater bacterium Caulobacter crescentus and with a freshwater microbial community using a combination of single- and double-stain flow cytometric assays. Growth of C.  crescentus and the freshwater community were repressed by triclosan but not by penconazole or metalaxyl at concentrations up to 250 μM. The repressive effect of triclosan was dependent on culture conditions. Caulobacter crescentus was more sensitive to triclosan when grown with high glucose at high cell density than when grown directly in sterilized lake water at low cell density. This suggests that the use of conventional growth conditions may overestimate biocide toxicity. Additional experiments showed that the freshwater community was more sensitive to triclosan than C.  crescentus, with 10 nM of triclosan being sufficient to repress growth and change the phylogenetic composition of the community. These results demonstrate that isolate-based assays may underestimate biocide toxicity and highlight the importance of assessing toxicity directly on natural microbial communities. Because 10 nM of triclosan is within the range of concentrations observed in freshwater systems, these results also raise concerns about the risk of introducing triclosan into the environment.

In vitro study of the effect of cationic biocides on bacterial population dynamics and susceptibility

Cationic biocides (CBs) are widely used in domestic and public hygiene and to control biofouling and microbial contamination in industry. The increased use of biocides has led to concern regarding possible reductions in biocide effectiveness. Domestic drain microcosms were stabilized for 5 months and then exposed to polyhexamethylene biguanide (PHMB) at 0.1, 0.2, and 0.4g liter(-1) over 6 months and characterized throughout by differential culture, together with eubacterial-specific PCR-denaturing gradient gel electrophoresis. Additionally, MICs and minimal bactericidal concentrations (MBCs) for bacteria previously isolated from a domestic drain (n = 18) and the human skin (n = 13) were determined before, during, and after escalating, sublethal exposure (14 passages) to two quaternary ammonium compounds (QAC1 and QAC2), the bisbiguanide chlorhexidine (CHX), and PHMB. Exposure of the drain microcosm to PHMB did not decrease the total viable count although significant (P < 0.01) decreases in recovery were observed for the gram-positive cocci with associated clonal expansion of pseudomonads (from ca. 0.1% of the population to ca. 10%). This clonal expansion was also manifested as elevations in bacteria that could grow in the presence of PHMB, CHX, and QAC1. Decreases in susceptibility (greater than twofold) occurred for 10/31 of the test bacteria for QAC1, 14/31 for QAC2, 10/31 for CHX, and 7/31 for PHMB. Exposure of microcosms to PHMB targeted gram-positive species and caused the clonal expansion of pseudomonads. In terms of prolonged-sublethal passage on CBs, exposure to all the biocides tested resulted in susceptibility decreases for a proportion of test bacteria, but refractory clones were not generated.

Reduced Susceptibility of Proteus mirabilis to triclosan

Clinical isolates of Proteus mirabilis causing catheter encrustation and blockage are susceptible to the biocide triclosan (MICs of 0.2 mg/liter). Studies with laboratory models of the bladder have demonstrated that the inflation of catheter retention balloons with triclosan solutions rather than water results in the diffusion of triclosan from the balloons into the surrounding urine and the inhibition of catheter encrustation by P. mirabilis. The aim of this study was to test whether the exposure of P. mirabilis to triclosan under laboratory conditions resulted in the selection of strains with reduced susceptibilities to this biocide. Exposure to triclosan in agar was shown to select mutants with MICs elevated from 0.2 mg/liter up to 80 mg/liter. In a selection of 14 of these strains, the decreased susceptibility was found to be stable and not associated with increased resistance to antibiotics. Experiments with the laboratory models demonstrated that inflation of the catheter balloons with triclosan (10 mg/ml) prevented encrustation and blockage by the parent strain P. mirabilis B2 (MIC, 0.2 mg/liter) and the mutant strain M48 (MIC, 2.0 mg/liter) but had no effect on crystalline biofilm formation by strain M55 (MIC, 40 mg/liter). These results suggest that, in any clinical trial or subsequent clinical use of the strategy, it will be important to monitor the urinary flora of the catheterized patients for P. mirabilis strains with reduced susceptibility to triclosan. The emergence of these strains could undermine the ability of the triclosan strategy to control catheter encrustation.

Consumer antibacterial soaps: effective or just risky?

BACKGROUND

Much has been written recently about the potential hazards versus benefits of antibacterial (biocide)-containing soaps. The purpose of this systematic literature review was to assess the studies that have examined the efficacy of products containing triclosan, compared with that of plain soap, in the community setting, as well as to evaluate findings that address potential hazards of this use--namely, the emergence of antibiotic-resistant bacteria.

METHODS

The PubMed database was searched for English-language articles, using relevant keyword combinations for articles published between 1980 and 2006. Twenty-seven studies were eventually identified as being relevant to the review.

RESULTS

Soaps containing triclosan within the range of concentrations commonly used in the community setting (0.1%-0.45% wt/vol) were no more effective than plain soap at preventing infectious illness symptoms and reducing bacterial levels on the hands. Several laboratory studies demonstrated evidence of triclosan-adapted cross-resistance to antibiotics among different species of bacteria.

CONCLUSIONS

The lack of an additional health benefit associated with the use of triclosan-containing consumer soaps over regular soap, coupled with laboratory data demonstrating a potential risk of selecting for drug resistance, warrants further evaluation by governmental regulators regarding antibacterial product claims and advertising. Further studies of this issue are encouraged.

Common therapeutic approaches for the control of oral biofilms: microbiological safety and efficacy

Triclosan is widely employed in many consumer and healthcare products. The increasing employment of triclosan in a range of consumer products where there is no proven benefit for hygiene has been severely criticised. Laboratory studies demonstrate theoretical risks that the wide-scale use of triclosan might compromise its efficacy as well as the activity of third-party antibiotics. The precautionary principle would dictate against the use of triclosan, at least in those products where there was no demonstrable health benefit. The theoretical risks, however, are not supported by either field or clinical studies, or by laboratory studies using bacterial microcosms. Numerous clinical studies, as well as historical data, demonstrate the clinical benefits of hygiene adjuncts such as triclosan and triclosan/copolymer in oral care products where these compensate for deficiencies in mechanical hygiene (brushing and flossing). The balance of risk and benefit is firmly in favour of the continued use of dentifrices (toothpastes) and mouthwashes containing active agents such as triclosan.

Antimicrobial susceptibility of Listeria monocytogenes from food products

This study was conducted to determine the susceptibility of Listeria monocytogenes isolated from food products to antimicrobial agents commonly used for treatment of infections with gram-positive bacteria, and to disinfectants. A total of 114 L. monocytogenes retail isolates were tested for susceptibility to ceftiofur, chloramphenicol, ciprofloxacin, erythromycin, florfenicol, penicillin, spectinomycin, streptomycin, tetracycline, tiamulin, trimethoprim, and co-trimoxazole, and the disinfectants benzalkonium chloride and triclosan, by determination of minimum inhibitory concentrations (MICs). All isolates were resistant to ceftiofur, but susceptible to the other antibiotics. A single isolate had a MIC of 4 mg/L for ciprofloxacin. For tiamulin. the MIC values were around the breakpoint used. Most isolates had MICs for triclosan at 16 mg/L. The MICs for benzalkonium chloride formed a bimodal distribution, with 105 isolates having a MIC of 4 mg/L and 9 isolates MICs of 16 and 32 mg/L. This study showed that Danish isolates of L. monocytogenes have not developed or acquired resistance to antimicrobial agents used for treatment or disinfection, except for benzalkonium chloride. The MICs for triclosan was high compared to other gram-positive bacteria, suggesting that triclosan might not be useful against L. monocytogenes if incorporated in materials in the food industry.