Specific variations of fatty acid composition of Pseudomonas aeruginosa ATCC 15442 induced by quaternary ammonium compounds and relation with resistance to bactericidal activity

Biocides in the Hospital Environment: Application and Tolerance Development

Hospital-acquired infections are a rising problem with consequences for patients, hospitals, and health care workers. Biocides can be employed to prevent these infections, contributing to eliminate or reduce microorganisms' concentrations at the hospital environment. These antimicrobials belong to several groups, each with distinct characteristics that need to be taken into account in their selection for specific applications. Moreover, their activity is influenced by many factors, such as compound concentration and the presence of organic matter. This article aims to review some of the chemical biocides available for hospital infection control, as well as the main factors that influence their efficacy and promote susceptibility decreases, with the purpose to contribute for reducing misusage and consequently for preventing the development of resistance to these antimicrobials.

Phenotypic, genotypic, and metabolic resistance mechanisms of ESKAPE bacteria to chemical disinfectants: a systematic review and meta-analysis

BACKGROUND

The presence of resistant ESKAPE pathogens to antimicrobials including chemical disinfectants (ChDs) is a serious threat to public health worldwide. In the present study, we systematically reviewed published reports on mechanisms beyond ChD resistance of ESKAPE bacteria.

RESEARCH DESIGN AND METHODS

Several databases without date limitations were searched. Studies focused on the ChD resistance/tolerance mechanisms of ESKAPE bacteria were included. Meta-analysis was done to assess the frequency of tolerance and genes in ESKAPE clinical isolates. By screening of initial 6733 records, finally, 41 studies were included.

RESULTS

The overall tolerance to at least one ChD was 48.6%. Pseudomonas aeruginosa and Acinetobacter baumannii were highly ChD-resistant. In several studies, phenotypic changes including changes in general morphology, pump function, cell surface, and membrane, as well as metabolic changes were observed after ChD addition. The resistance gene frequency was 70.2% for norfloxacin efflux pump genes, 40.6% for qac major facilitator superfamily genes, and 22.2% for qac small multidrug resistance genes.

CONCLUSION

We systematically reviewed the effect of various mechanisms in the resistance process of ESKAPE bacteria to ChDs. However, except for the impact of genes, the numbers of studies investigating other mechanisms were very limited, demanding carrying out more studies in this field.

Quaternary ammonium disinfectants and antiseptics: tolerance, resistance and potential impact on antibiotic resistance

BACKGROUND

Due to the substantial increase in the use of disinfectants containing quaternary ammonion compounds (QACs) in healthcare and community settings during the COVID-19 pandemic, there is increased concern that heavy use might cause bacteria to develop resistance to QACs or contribute to antibiotic resistance. The purpose of this review is to briefly discuss the mechanisms of QAC tolerance and resistance, laboratory-based evidence of tolerance and resistance, their occurrence in healthcare and other real-world settings, and the possible impact of QAC use on antibiotic resistance.

METHODS

A literature search was conducted using the PubMed database. The search was limited to English language articles dealing with tolerance or resistance to QACs present in disinfectants or antiseptics, and potential impact on antibiotic resistance. The review covered the period from 2000 to mid-Jan 2023.

RESULTS

Mechanisms of QAC tolerance or resistance include innate bacterial cell wall structure, changes in cell membrane structure and function, efflux pumps, biofilm formation, and QAC degradation. In vitro studies have helped elucidate how bacteria can develop tolerance or resistance to QACs and antibiotics. While relatively uncommon, multiple episodes of contaminated in-use disinfectants and antiseptics, which are often due to inappropriate use of products, have caused outbreaks of healthcare-associated infections. Several studies have identified a correlation between benzalkonium chloride (BAC) tolerance and clinically-defined antibiotic resistance. The occurrence of mobile genetic determinants carrying multiple genes that encode for QAC or antibiotic tolerance raises the concern that widespread QAC use might facilitate the emergence of antibiotic resistance. Despite some evidence from laboratory-based studies, there is insufficient evidence in real-world settings to conclude that frequent use of QAC disinfectants and antiseptics has promoted widespread emergence of antibiotic resistance.

CONCLUSIONS

Laboratory studies have identified multiple mechanisms by which bacteria can develop tolerance or resistance to QACs and antibiotics. De novo development of tolerance or resistance in real-world settings is uncommon. Increased attention to proper use of disinfectants is needed to prevent contamination of QAC disinfectants. Additional research is needed to answer many questions and concerns related to use of QAC disinfectants and their potential impact on antibiotic resistance.

Biocide-tolerance and antibiotic-resistance in community environments and risk of direct transfers to humans: Unintended consequences of community-wide surface disinfecting during COVID-19?

During the current pandemic, chemical disinfectants are ubiquitously and routinely used in community environments, especially on common touch surfaces in public settings, as a means of controlling the virus spread. An underappreciated risk in current regulatory guidelines and scholarly discussions, however, is that the persisting input of chemical disinfectants can exacerbate the growth of biocide-tolerant and antibiotic-resistant bacteria on those surfaces and allow their direct transfers to humans. For COVID-19, the most commonly used disinfecting agents are quaternary ammonium compounds, hydrogen peroxide, sodium hypochlorite, and ethanol, which account for two-thirds of the active ingredients in current EPA-approved disinfectant products for the novel coronavirus. Tolerance to each of these compounds, which can be either intrinsic or acquired, has been observed on various bacterial pathogens. Of those, mutations and horizontal gene transfer, upregulation of efflux pumps, membrane alteration, and biofilm formation are the common mechanisms conferring biocide tolerance in bacteria. Further, the linkage between disinfectant use and antibiotic resistance was suggested in laboratory and real-life settings. Evidence showed that substantial bacterial transfers to hands could effectuate from short contacts with surrounding surfaces and further from fingers to lips. While current literature on disinfectant-induced antimicrobial resistance predominantly focuses on municipal wastes and the natural environments, in reality the community and public settings are most severely impacted by intensive and regular chemical disinfecting during COVID-19 and, due to their proximity to humans, biocide-tolerant and antibiotic-resistant bacteria emerged in these environments may pose risks of direct transfers to humans, particularly in densely populated urban communities. Here we highlight these risk factors by reviewing the most pertinent and up-to-date evidence, and provide several feasible strategies to mitigate these risks in the scenario of a prolonging pandemic.

Activity of Liquid and Volatile Fractions of Essential Oils against Biofilm Formed by Selected Reference Strains on Polystyrene and Hydroxyapatite Surfaces

Biofilms are surface-attached, structured microbial communities displaying higher tolerance to antimicrobial agents in comparison to planktonic cells. An estimated 80% of all infections are thought to be biofilm-related. The drying pipeline of new antibiotics efficient against biofilm-forming pathogens urges the search for alternative routes of treatment. Essential Oils (EOs), extracted from medicinally important plants, are a reservoir of bioactive compounds that may serve as a foothold in investigating novel antibiofilm compounds. The aim of this study was to compare antimicrobial activity of liquid and volatile fractions of tested EOs against biofilm-forming pathogens using different techniques. In this research, we tested five EOs, extracted from Syzygium aromaticum L., Boswelia serrata Roxb., Juniperus virginiana L., Pelargonium graveolens L. and Melaleuca alternifolia Cheel., against planktonic and biofilm forms of five selected reference strains, namely Staphylococcus aureus, Enterococcus faecalis, Klebsiella pneumoniae, Pseudomonas aeruginosa, Escherichia coli, and Candida albicans. To obtain cohesive results, we applied four various methodological approaches: to assess the activity of the liquid fraction of EOs, disc diffusion and the microdilution method were applied; to test EOs’ volatile fraction, the AntiBioVol assay and modified Antibiofilm Dressing Activity Measurement (A.D.A.M.) were used. The molecular composition and dynamics of antimicrobial substances released from specific EOs was measured using Gas Chromatography–Mass Spectrometry (GC-MS). The antimicrobial potency of EO’s volatile fraction against biofilm formed by tested strains differed from that of the liquid fraction and was related to the molecular weight of volatile compounds. The liquid fraction of CW-EO and volatile fraction of F-EO acted in the strongest manner against biofilm of C. albicans. The addition of 0.5% Tween 20 to liquid phase, enhanced activity of G-EO against E. coli and K. pneumoniae biofilm. EO activity depended on the microbial species it was applied against and the chosen assessment methodology. While all tested EOs have shown a certain level of antimicrobial and antibiofilm effect, our results indicate that the choice of EO to be applied against a specific biofilm-forming pathogen requires careful consideration with regard to the above-listed aspects. Nevertheless, the results presented in this research contribute to the growing body of evidence indicating the beneficial effects of EOs, which may be applied to fight biofilm-forming pathogens.

Multifunctional cationic surfactants with a labile amide linker as efficient antifungal agents-mechanisms of action

Our research aimed to expand the knowledge of relationships between the structure of multifunctional cationic dicephalic surfactants with a labile linker-N,N-bis[3,3-(dimethylamine)propyl]alkylamide dihydrochlorides and N,N-bis[3,3-(trimethylammonio)propyl]alkylamide dibromides (alkyl: n-C₉H₁₉, n-C₁₁H₂₃, n-C₁₃H₂₇, n-C₁₅H₃₁)-and their possible mechanism of action on fungal cells using the model organism Saccharomyces cerevisiae. General studies performed on surfactants suggest that in most cases, their main mechanism of action is based on perforation of the cell membranes and cell disruption. Experiments carried out in this work with cationic dicephalic surfactants seem to modify our understanding of this issue. It was found that the investigated compounds did not cause perforation of the cell membrane and could only interact with it, increasing its permeability. The surfactants tested can probably penetrate inside the cells, causing numerous morphological changes, and contribute to disorders in the lipid metabolism of the cell resulting in the formation of lipid droplet aggregates. This research also showed that the compounds cause severe oxidative stress within the cells studied, including increased production of superoxide anion radicals and mitochondrial oxidative stress. Dicephalic cationic surfactants due to their biodegradability do not accumulate in the environment and in the future may be used as effective antifungal compounds in industry as well as medicine, which will be environmentally friendly. KEY POINTS: • Dicephalic cationic surfactants do not induce disruption of the cell membrane. • Surfactants could infiltrate into the cells and cause accumulation of lipids. • Surfactants could cause acute oxidative stress in yeast cells. • Compounds present multimodal mechanism of action. Graphical abstract.

Biological activity of quaternary ammonium salts and resistance of microorganisms to these compounds

Quaternary ammonium salts (QASs) are ubiquitous in nature, being found in organisms ranging from microorganisms to vertebrates (e.g., glycine betaine, carnitine) where they have important cellular functions. QASs are also obtained by chemical synthesis. These compounds, due to their diverse chemical structure (e.g. monomeric QAS or gemini) and their biological properties, are widely used in medicine (as disinfectants, drugs, and DNA carriers), industry, environmental protection and agriculture (as preservatives, biocides, herbicides and fungicides). Discussed chemical compounds reduce the adhesion of microorganisms to various biotic and abiotic surfaces and cause the eradication of biofilms produced by pathogenic microorganisms. The properties of these chemicals depend on their chemical structure (length of the alkyl chain, linker and counterion), which has a direct impact on the physicochemical and biological activity of these compounds. QASs by incorporation into the membranes, inhibit the activity of proteins (H⁺-ATPase) and disrupt the transport of substances to the cell. Moreover, in the presence of QASs, changes in lipid composition (qualitative and quantitative) of plasma membrane are observed. The widespread use of disinfectants in commercial products can induce resistance in microorganisms to these surfactants and even to antibiotics. In this article we discuss the biological activity of QASs as cationic surfactants against microorganisms and their resistance to these compounds.

Sulfenate Esters of Simple Phenols Exhibit Enhanced Activity against Biofilms

The recalcitrance exhibited by microbial biofilms to conventional disinfectants has motivated the development of new chemical strategies to control and eradicate biofilms. The activities of several small phenolic compounds and their trichloromethylsulfenyl ester derivatives were evaluated against planktonic cells and mature biofilms of Staphylococcus epidermidis and Pseudomonas aeruginosa. Some of the phenolic parent compounds are well-studied constituents of plant essential oils, for example, eugenol, menthol, carvacrol, and thymol. The potency of sulfenate ester derivatives was markedly and consistently increased toward both planktonic cells and biofilms. The mean fold difference between the parent and derivative minimum inhibitory concentration against planktonic cells was 44 for S. epidermidis and 16 for P. aeruginosa. The mean fold difference between the parent and derivative biofilm eradication concentration for 22 tested compounds against both S. epidermidis and P. aeruginosa was 3. This work demonstrates the possibilities of a new class of biofilm-targeting disinfectants deploying a sulfenate ester functional group to increase the antimicrobial potency toward microorganisms in biofilms.

Resistance of Bacteria to Biocides

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

Light-activated phenalen-1-one bactericides: efficacy, toxicity and mechanism compared with benzalkonium chloride

Aim: Five photoactive compounds with variable elongated alkyl-substituents in a phenalen-1-one structure were examined in view of structural similarity to the antimicrobial agent benzalkonium chloride (BAC). Methods: All phenalen-1-ones and BAC were evaluated for their antimicrobial properties against Staphylococcus aureus, methicillin-resistant S. aureus, Escherichia coli, Pseudomonas aeruginosa and for their eukaryotic toxicity against normal human epidermal keratinocyte (NHEK) cells to narrow down the BAC-like effect and the photodynamic effect depending on the chemical structure. All compounds were investigated for effective concentration ranges, where a bacterial reduction of 5 log10 is achieved, while an NHEK survival of 80% is ensured. Results: Effective concentration ranges were found for four out of five photoactive compounds, but not for BAC and the compound with BAC-like alkyl chain length. Conclusion: Chain length size and polar area of the respective head-groups of phenalen-1-one compounds or BAC showed an influence on the incorporation inside lipid membranes and thus, head-groups may have an impact on the toxicity of antimicrobials.

Prevention of biofilm formation by polyquaternary polymer

OBJECTIVE

Biofilm formation has been linked to device-associated infections in otolaryngology. This study was conducted to determine if a microbicidal polyquaternary polymer, poly diallyl-dimethylammonium chloride (pDADMAC) could prevent biofilm development by pathogens that commonly cause implant infections, Staphylococcus aureus and Pseudomonas aeruginosa.

METHODS AND MATERIALS

This study was prospective and controlled in vitro microbiological study. Polyurethane tubes (20 per treatment) with and without a polyquaternary polymer coating were briefly exposed to plasma or saline, then to S. aureus or P. aeruginosa. Polyurethane tubes were incubated in growth media. After 4 days, antibiotics were added to kill planktonic bacteria. S. aureus or P. aeruginosa bacterial counts and scanning electron microscopy (SEM) were performed.

RESULTS

S. aureus biofilm counts were reduced by 8 logs on tubes with polyquaternary polymer coating compared to the control tubes, either with plasma (3.67E+01 ± 7.30E+01 vs 1.08E+09 ± 4.81E+08; P < 0.0001) or without plasma (3.70E+00 ± 1.10E+01 vs 6.50E+08 ± 2.79E+08; P < 0.0001). P. aeruginosa biofilm formation was also reduced on tubes with polyquaternary polymer, either with plasma (2.90E+07 ± 1.71E+07 vs 9.16E+08 ± 4.43E+08; P < 0.0001) or without plasma (2.50E+07 ± 9.54E+06 vs 3.35E+08 ± 2.18E+08; P < 0.001), but the reduction was only 1 log. On control tubes, plasma promoted S. aureus (1.08E+09 ± 4.81E+08 vs 6.05E+08 ± 2.79E+08; P < 0.0001) and P. aeruginosa (9.16E+08 ± 4.43E+08 vs 3.35E+08 ± 2.18E+08; P < 0.0001) bacterial counts but not on the tubes coated with polyquaternary polymer.

CONCLUSIONS

Incorporation of the microbicidal polyquaternary polymer, pDADMAC, into polyurethane dramatically inhibits S. aureus biofilm formation. Further research is warranted to evaluate the efficacy and safety of this technology in otolaryngologic implants.

Adaptive tolerance to phenolic biocides in bacteria from organic foods: Effects on antimicrobial susceptibility and tolerance to physical stresses

The aim of the present study was to analyze the effects of step-wise exposure of biocide-sensitive bacteria from organic foods to phenolic biocides triclosan (TC) and hexachlorophene [2,2'-methylenebis(3,4,6-trichlorophenol)] (CF). The analysis included changes in the tolerance to the biocide itself, the tolerance to other biocides, and cross-resistance to clinically important antibiotics. The involvement of efflux mechanisms was also studied as well as the possible implication of modifications in cytoplasmic membrane fluidity in the resistance mechanisms. The influence of biocide tolerance on growth capacity of the adapted strains and on subsequent resistance to other physical stresses has also been analyzed. Repeated exposure of bacteria from organic foods to phenolic biocides resulted in most cases in partially increased tolerance to the same biocide, to dissimilar biocides and other antimicrobial compounds. Nine TC-adapted strains and six CF-adapted strains were able to develop high levels of biocide tolerance, and these were stable in the absence of biocide selective pressure. Most strains adapted to TC and one CF-adapted strain showed significantly higher anisotropy values than their corresponding wildtype strains, suggesting that changes in membrane fluidity could be involved in biocide adaptation. Exposure to gradually increasing concentrations of CF induced a decrease in heat tolerance. Biocide adaptation had no significant effects of gastric acid or bile resistance, suggesting that biocide adaptation should not influence survival in the gastrointestinal tract.

Coordinated response of phospholipids and acyl components of membrane lipids in Pseudomonas putida A (ATCC 12633) under stress caused by cationic surfactants

The present study assessed the role of membrane components of Pseudomonas putida A (ATCC 12633) under chemical stress conditions originated by treatment with tetradecyltrimethylammonium bromide (TTAB), a cationic surfactant. We examined changes in fatty acid composition and in the fluidity of the membranes of cells exposed to TTAB at a specific point of growth as well as of cells growing with TTAB. The addition of 10-50 mg TTAB l(-1) promoted an increase in the saturated/unsaturated fatty acid ratio. By using fluorescence polarization techniques, we found that TTAB exerted a fluidizing effect on P. putida A (ATCC 12633) membranes. However, a complete reversal of induced membrane fluidification was detected after 15 min of incubation with TTAB. Consistently, the proportion of unsaturated fatty acids was lower in TTAB-treated cells as compared with non-treated cells. In the presence of TTAB, the content of phosphatidylglycerol increased (120 %), whilst that of cardiolipin decreased (60 %). Analysis of the fatty acid composition of P. putida A (ATCC 12633) showed that phosphatidylglycerol carried the major proportion of saturated fatty acids (89 %), whilst cardiolipin carried an elevated proportion of unsaturated fatty acids (18 %). The increase in phosphatidylglycerol and consequently in saturated fatty acids, together with a decrease in cardiolipin content, enabled greater membrane resistance, reversing the fluidizing effect of TTAB. Therefore, results obtained in the present study point to changes in the fatty acid profile as an adaptive response of P. putida A (ATCC 12633) cells to stress caused by a cationic surfactant.

Biocide tolerance in bacteria

Biocides have been employed for centuries, so today a wide range of compounds showing different levels of antimicrobial activity have become available. At the present time, understanding the mechanisms of action of biocides has also become an important issue with the emergence of bacterial tolerance to biocides and the suggestion that biocide and antibiotic resistance in bacteria might be linked. While most of the mechanisms providing antibiotic resistance are agent specific, providing resistance to a single antimicrobial or class of antimicrobial, there are currently numerous examples of efflux systems that accommodate and, thus, provide tolerance to a broad range of structurally unrelated antimicrobials, both antibiotics and biocides. If biocide tolerance becomes increasingly common and it is linked to antibiotic resistance, not only resistant (even multi-resistant) bacteria could be passed along the food chain, but also there are resistance determinants that can spread and lead to the emergence of new resistant microorganisms, which can only be detected and monitored when the building blocks of resistance traits are understood on the molecular level. This review summarizes the main advances reached in understanding the mechanism of action of biocides, the mechanisms of bacterial resistance to both biocides and antibiotics, and the incidence of biocide tolerance in bacteria of concern to human health and the food industry.

Biocides--resistance, cross-resistance mechanisms and assessment

IMPORTANCE OF THE FIELD

Antibiotic resistance in bacterial pathogens has increased worldwide leading to treatment failures. Concerns have been raised about the use of biocides as a contributing factor to the risk of antimicrobial resistance (AMR) development. In vitro studies demonstrating increase in resistance have often been cited as evidence for increased risks. It is therefore important to understand the mechanisms of resistance employed by bacteria toward biocides used in consumer products and their potential to impart cross-resistance to therapeutic antibiotics.

AREAS COVERED

In this review, the mechanisms of resistance and cross-resistance reported in the literature toward biocides commonly used in consumer products are summarized. The physiological and molecular techniques used in describing and examining these mechanisms are reviewed and application of these techniques for systematic assessment of biocides for their potential to develop resistance and/or cross-resistance is discussed.

EXPERT OPINION

The guidelines in the usage of biocides in household or industrial purpose should be monitored and regulated to avoid the emergence of any MDR strains. The genetic and molecular methods to monitor the resistance development to biocides should be developed and included in preclinical and clinical studies.

Assessment of the working range and effect of sodium dichloroisocyanurate on Pseudomonas aeruginosa biofilms and planktonic cells

Sodium dichloroisocyanurate (NaDCC) is a chemical agent that acts against microorganisms in a manner similar to that of sodium hypochlorite by releasing free available chlorine. NaDCC has been approved by the WHO for the emergency treatment of water and by the US EPA for routine treatment of water. Previous studies assessing the effectiveness of NaDCC for the treatment of water implied that NaDCC should have a wide array of disinfecting effects beyond the treatment of planktonic cells in potable water. In this study the biocidal effects of NaDCC against Pseudomonas aeruginosa cells in different growth modes including planktonic cells and biofilms were explored. The data showed that a 60% dilution of the standard NaDCC solution was effective in the treatment of both P. aeruginosa planktonic cells and biofilms.

Resistance of bacterial biofilms to disinfectants: a review

A biofilm can be defined as a community of microorganisms adhering to a surface and surrounded by a complex matrix of extrapolymeric substances. It is now generally accepted that the biofilm growth mode induces microbial resistance to disinfection that can lead to substantial economic and health concerns. Although the precise origin of such resistance remains unclear, different studies have shown that it is a multifactorial process involving the spatial organization of the biofilm. This review will discuss the mechanisms identified as playing a role in biofilm resistance to disinfectants, as well as novel anti-biofilm strategies that have recently been explored.

Comparative biocidal activity of peracetic acid, benzalkonium chloride and ortho-phthalaldehyde on 77 bacterial strains

Despite numerous reports on biocide activities, it is often difficult to have a reliable and relevant overview of bacterial resistance to disinfectants because each work challenges a limited number of strains and tested methods are often different. The aim of this study was to evaluate the bactericidal activity of three different disinfectants commonly used in industrial or medical environments (peracetic acid, benzalkonium chloride and ortho-phthalaldehyde) against 77 bacterial strains from different origins using one standard test method (NF EN 1040). Results highlight the existence of high interspecific variability of resistance to disinfectants and, contrary to widespread belief, Gram-positive strains generally appeared more resistant than Gram-negative strains. Resistance was also variable among strains of the same species such as Bacillus subtilis to peracetic acid, Pseudomonas aeruginosa to benzalkonium chloride and Staphylococcus aureus to ortho-phthalaldehyde.

The physiological and morphological phenotype of a yeast mutant resistant to the quaternary ammonium salt N-(dodecyloxycarboxymethyl)-N,N,N-trimethyl ammonium chloride

We investigated the action of the quaternary ammonium salt (QAS) called IM (N-(dodecyloxycarboxymethyl)-N,N,N-trimethyl ammonium chloride) on Saccharomyces cerevisiae yeast cells. Changes in the yeast cell ultrastructure were confirmed by electron microscopy. We treated resistant mutant cells with QAS, and confirmed destruction of the mutant cytoplasm, an increase in the thickness of the cell wall, separation of the cell wall from the cytoplasm, and the accumulation of numerous lipid droplets. We also observed a relatively high production of lipids in the cells of the parental wild-type strain Sigma1278b and in its IM-resistant (IM(R)) mutant in the presence of the QAS. The IM(R) mutant showed increased sensitivity to CaCl(2) and SDS, and resistance to ethidium bromide, chloramphenicol, erythromycin and osmotic shock. It also tolerated growth at low pH. We suggest that the resistance to IM could be connected with the level of permeability of the cell membrane because the IM(R) mutant was sensitive to this compound in vivo in the presence of SDS and guanidine hydrochloride, which cause increased permeability of the cell plasma membrane.

Morphological and biochemical changes in Pseudomonas fluorescens biofilms induced by sub-inhibitory exposure to antimicrobial agents

Confocal laser scanning microscopy (CLSM) and scanning transmission X-ray microscopy (STXM) were used to examine the morphological and biochemical changes in Pseudomonas fluorescens biofilms grown in the presence of subinhibitory concentrations of 4 antimicrobial agents: triclosan, benzalkonium chloride, chlorhexidine dihydrochloride, and trisodium phosphate. CLSM analyses using the stains SYTO9 and propidium iodide indicated that the antimicrobial agents affected cell membrane integrity and cellular density to differing degrees. However, fluorescein diacetate assays and plate counts demonstrated that the cells remained metabolically active. Fluorescent lectin binding assays showed that changes in the arrangement and composition of the exopolymer matrix of the biofilms also occurred and that these changes depended on the antimicrobial agent. Detailed single cell analyses using STXM provided evidence that the cell morphology, and the spatial distribution and relative amounts of protein, lipids and polysaccharides in the biofilms and within the cells were different for each antimicrobial. The distribution of chlorhexidine in the biofilm, determined from its distinct spectral signature, was localized mainly inside the bacterial cells. Each antimicrobial agent elicited a unique response; P. fluorescens cells and biofilms changed their morphology and architecture, as well as the distribution and abundance of biomacromolecules, in particular the exopolymer matrix. Pseudomonas fluorescens also exhibited adaptation to benzalkonium chloride at 10 microg/mL. Our observations point to the importance of changes in the quantity and chemistry of the exopolymeric matrix in the response to antimicrobial agents and suggest their importance as targets for control.

Copper and quaternary ammonium cations exert synergistic bactericidal and antibiofilm activity against Pseudomonas aeruginosa

Biofilms are slimy aggregates of microbes that are likely responsible for many chronic infections as well as for contamination of clinical and industrial environments. Pseudomonas aeruginosa is a prevalent hospital pathogen that is well known for its ability to form biofilms that are recalcitrant to many different antimicrobial treatments. We have devised a high-throughput method for testing combinations of antimicrobials for synergistic activity against biofilms, including those formed by P. aeruginosa. This approach was used to look for changes in biofilm susceptibility to various biocides when these agents were combined with metal ions. This process identified that Cu(2+) works synergistically with quaternary ammonium compounds (QACs; specifically benzalkonium chloride, cetalkonium chloride, cetylpyridinium chloride, myristalkonium chloride, and Polycide) to kill P. aeruginosa biofilms. In some cases, adding Cu(2+) to QACs resulted in a 128-fold decrease in the biofilm minimum bactericidal concentration compared to that for single-agent treatments. In combination, these agents retained broad-spectrum antimicrobial activity that also eradicated biofilms of Escherichia coli, Staphylococcus aureus, Salmonella enterica serovar Cholerasuis, and Pseudomonas fluorescens. To investigate the mechanism of action, isothermal titration calorimetry was used to show that Cu(2+) and QACs do not interact in aqueous solutions, suggesting that each agent exerts microbiological toxicity through independent biochemical routes. Additionally, Cu(2+) and QACs, both alone and in combination, reduced the activity of nitrate reductases, which are enzymes that are important for normal biofilm growth. Collectively, the results of this study indicate that Cu(2+) and QACs are effective combinations of antimicrobials that may be used to kill bacterial biofilms.

Modification of phospholipid composition in Pseudomonas putida A ATCC 12633 induced by contact with tetradecyltrimethylammonium

AIMS

The aim of this work was to establish if the response to tetradecyltrimethylammonium (TDTMA), a representative quaternary ammonium compound (QAC), involves changes in the phospholipid (PL) composition of Pseudomonas putida A ATCC 12633.

METHODS AND RESULTS

Pseudomonas putida was exposed to 50 mg l(-1) of TDTMA for 15 min, and PL composition was analysed. With respect to control values, phosphatidic acid and phosphatidylglycerol increased by 140% and 120%, respectively; cardiolipin decreased about 60%. In TDTMA-adapted bacteria, the most significant change was a 380% increase in phosphatidic acid. Accompanying this change was a 130% increase in phosphatidylglycerol and a 70% decrease in cardiolipin. The changes in adapted cells were reverted after two subcultures without biocide.

CONCLUSIONS

Pseudomonas putida responded to TDTMA through quantitative changes in PLs with specific variations in the content of phosphatidic acid, phosphatidylglycerol and cardiolipin. These modifications indicated that these PLs are involved in cellular responses to QACs, utilizing phosphatidic acid principally to neutralize the high positive charge density given for the ammonium quaternary moiety from TDTMA.

SIGNIFICANCE AND IMPACT OF THE STUDY

The changes in PL composition give a new insight about the response inflicted by Ps. putida when these bacteria are exposed to QACs.

Fate and effect of quaternary ammonium compounds on a mixed methanogenic culture

The potential inhibitory effect of four quaternary ammonium compounds (QACs) and Vigilquat, a commercial sanitizer which is a mixture of the four QACs, was investigated at concentrations up to 100 mg/L using a mixed, mesophilic (35 degrees C) methanogenic culture. Dextrin and peptone were used as the carbon and energy sources. A batch assay conducted at a range of QAC concentrations showed that QACs were inhibitory to methanogens at and above 25 mg/L. Methanogenesis was more susceptible to QAC inhibition than acidogenesis. Adsorption of QACs on biomass was successfully simulated with the Freundlich isotherm equation. The inhibitory effect of Vigilquat on the mixed methanogenic culture was also investigated in a batch reactor fed with dextrin and peptone. Methanogens were inhibited when the total QAC concentration reached 30 mg/L and volatile fatty acids (VFAs) accumulated. However, methane production recovered in 57 days of incubation, and all VFAs were consumed, suggesting that a prolonged incubation period is necessary for the methanogens to overcome the transient inhibition at a relatively low QAC concentration. None of the QACs tested in this study was biodegraded under methanogenic conditions.

Adaptive changes in fatty acids ofE. coli strains exposed to a quaternary ammonium salt and an amine oxide

Resistant strains of Escherichia coli were obtained by stepwise cultivation in media with increasing concentration of antimicrobially active 1-(methyldodecyl)dimethylamine oxide and 1-(methyldodecyl)trimethylammonium bromide. Adaptive changes were determined in the fatty-acid (FA) composition in an isolated lipopolysaccharide sample from the outer membrane of these strains. The composition of this FA mixture from adapted strains was compared with that of FA from a sensitive strain. The differences were found in level of palmitic, heptadecanoic, heptadecenoic, heptadecadienoic and nonadecenoic acids. In addition, the adapted strains differed from each other in the content of myristic, pentadecanoic, stearic and linoleic acids.

Possible associations between Salmonella persistence in poultry houses and resistance to commonly used disinfectants and a putative role of mar

A putative link between Salmonella persistence in the agricultural sector and resistance to disinfectants has been sparsely investigated. Therefore, minimum inhibitory concentration (MIC) tests against five disinfectants commonly used in poultry premises (formaldehyde, glutaraldehyde/benzalkonium chloride compound, oxidising compound, tar oil phenol, iodophor) were performed on 286 Salmonella isolates, including 256 from Danish broiler houses, altogether representing nine serotypes. Six of these isolates were used for adaptation and de-adaptation studies involving the five disinfectants. Amongst 60 of these isolates selected for growth studies in cyclohexane (possibly associated with up-regulated efflux), only one isolate grew. From this isolate and the six isolates used in the adaptation and de-adaptation studies, mutants highly resistant to triclosan (a disinfectant linked with mar-type resistance) were selected. In addition, adaptation and de-adaptation studies with triclosan were performed. For the 286 isolates, the small variations in MICs could not be associated with Salmonella persistence in Danish broiler houses or previous use of relevant disinfectants. Adaptation and de-adaptation did not alter MICs to the five farm disinfectants. Compared to the parent isolates, MICs for the triclosan adapted and de-adapted isolates and the triclosan mutants were significantly increased to triclosan, but not to the five disinfectants. Moreover, most of the triclosan adapted and de-adapted isolates grew in cyclohexane. Thus, there was no correlation between triclosan and cyclohexane resistance on one hand and resistance to the five disinfectants on the other, suggesting that triclosan resistance is not linked with resistance to these disinfectants.

Altered sensitivity to a quaternary ammonium sanitizer in stressed Listeria innocua

Chemical sanitizers are commonly used to inactivate Listeria monocytogenes and other Listeria species that persist in food-processing environments after cleaning. In this study, Listeria innocua cultures were exposed to acid, heat, cold, and starvation stress and then assessed for sensitivity to the quaternary ammonium compound cetrimide. Unstressed and stressed cultures were exposed to cetrimide for 3 min, neutralized, and plated on tryptic soy agar with yeast extract to determine the percentage of survivors. Relative to controls, L. innocua exposed to acid and starvation conditions was less sensitive to cetrimide, whereas heat and cold stress increased cetrimide sensitivity (P < 0.05). The diminished sensitivity of acid- and starvation-stressed L. innocua to cetrimide suggests that these stressors might increase the persistence of this organism within food-manufacturing facilities. In contrast, enhanced L. innocua sensitivity to cetrimide following heat and cold stress suggests that these interventions might increase sanitation efficacy.

Resistance of spheroplasts and whole cells of Pseudomonas aeruginosa to bactericidal activity of various biocides: evidence of the membrane implication

To emphasise the role of outer and inner membranes in the resistance of Pseudomonas aeruginosa to bactericidal activity of various disinfectants, spheroplasts and whole cells were compared. Spheroplasts are more sensitive than whole cells to quaternary ammonium compounds such as didecyl dimethyl ammonium bromide (DDAB) and C16-benzalkonium chloride. The outer membrane acts as a barrier to prevent these disinfectants from entering the cell. It seems to have no influence on activities of smaller molecules such as C12, C14-benzalkonium chlorides and sodium dichloroisocyanurate. For tri-sodium phosphate, the presence of outer membrane emphasized the action of the molecule. Moreover, resistance of DDAB-adapted spheroplasts to bactericidal activity of DDAB is higher than the resistance of non-adapted spheroplasts. This suggests that the inner membrane could also play a role in resistance to DDAB.

Correlation between resistance of Pseudomonas aeruginosa to quaternary ammonium compounds and expression of outer membrane protein OprR

The adaptation mechanism of Pseudomonas aeruginosa ATCC 10145 to quaternary ammonium compounds (QACs) was investigated. A P. aeruginosa strain with adapted resistance to QACs was developed by a standard broth dilution method. It was revealed that P. aeruginosa exhibited remarkable resistance to N-dodecylpyridinium iodide (P-12), whose structure is similar to that of a common disinfectant, cetylpyridinium chloride. Adapted resistance to benzalkonium chloride (BAC), which is commonly used as a disinfectant, was also observed in P. aeruginosa. Moreover, the P-12-resistant strain exhibited cross-resistance to BAC. Analysis of the outer membrane protein of the P-12-resistant strain by two-dimensional polyacrylamide gel electrophoresis showed a significant increase in the level of expression of a protein (named OprR) whose molecular mass was approximately 26 kDa. The actual function of OprR is not yet clear; however, OprR was expected to be an outer membrane-associated protein with homology to lipoproteins of other bacterial species, according to a search of the National Center for Biotechnology Information website with the BLAST program by use of the N-terminal sequence of OprR. A correlation between the level of expression of OprR and the level of resistance of P. aeruginosa to QACs was observed by using a PA2800 gene knockout mutant derived from the P-12-resistant strain. The knockout mutant recovered susceptibility not only to P-12 but also to BAC. These results suggested that OprR significantly participated in the adaptation of P. aeruginosa to QACs, such as P-12 and BAC.

Correlation between resistance of Pseudomonas aeruginosa to quaternary ammonium compounds and expression of outer membrane protein OprR

The adaptation mechanism of Pseudomonas aeruginosa ATCC 10145 to quaternary ammonium compounds (QACs) was investigated. A P. aeruginosa strain with adapted resistance to QACs was developed by a standard broth dilution method. It was revealed that P. aeruginosa exhibited remarkable resistance to N-dodecylpyridinium iodide (P-12), whose structure is similar to that of a common disinfectant, cetylpyridinium chloride. Adapted resistance to benzalkonium chloride (BAC), which is commonly used as a disinfectant, was also observed in P. aeruginosa. Moreover, the P-12-resistant strain exhibited cross-resistance to BAC. Analysis of the outer membrane protein of the P-12-resistant strain by two-dimensional polyacrylamide gel electrophoresis showed a significant increase in the level of expression of a protein (named OprR) whose molecular mass was approximately 26 kDa. The actual function of OprR is not yet clear; however, OprR was expected to be an outer membrane-associated protein with homology to lipoproteins of other bacterial species, according to a search of the National Center for Biotechnology Information website with the BLAST program by use of the N-terminal sequence of OprR. A correlation between the level of expression of OprR and the level of resistance of P. aeruginosa to QACs was observed by using a PA2800 gene knockout mutant derived from the P-12-resistant strain. The knockout mutant recovered susceptibility not only to P-12 but also to BAC. These results suggested that OprR significantly participated in the adaptation of P. aeruginosa to QACs, such as P-12 and BAC.

Potential impact of increased use of biocides in consumer products on prevalence of antibiotic resistance

There has recently been much controversy surrounding the increased use of antibacterial substances in a wide range of consumer products and the possibility that, as with antibiotics, indiscriminate use of biocides might contribute to the overall pattern of susceptibility in the general environment and in the clinic. Such speculation, based on the isolation of resistant mutants from in vitro monoculture experiments, is not reflected by an emergence of biocide-resistant strains in vivo. This review provides a broad coverage of the biocide and resistance literature and evaluates the potential risks, perceived from such laboratory monoculture experiments, against evidence gathered over 50 years of field studies. An explanation for the continued effectiveness of broad-spectrum biocidal agents against the decline in efficacy of therapeutic agents is provided based on the fitness costs of resistance and the ubiquity of naturally occurring substances that possess antibacterial effect. While we conclude from this review of the literature that the incorporation of antibacterial agents into a widening sphere of personal products has had little or no impact on the patterns of microbial susceptibility observed in the environment, the associated risks remain finite. The use of such products should therefore be associated with a clear demonstration of added value either to consumer health or to the product life. Hygienic products should therefore be targeted to applications for which the risks have been established.