More QACs, more questions: Recent advances in structure activity relationships and hurdles in understanding resistance mechanisms

Synthesis and broad-spectrum biocidal effect of novel gemini quaternary ammonium compounds

Since the discovery of antimicrobial agents, the misuse of antibiotics has led to the emergence of bacterial strains resistant to both antibiotics and common disinfectants like quaternary ammonium compounds (QACs). A new class, 'gemini' QACs, which contain two polar heads, has shown promise. Octenidine (OCT), a representative of this group, is effective against resistant microorganisms but has limitations such as low solubility and high cytotoxicity. In this study, we developed 16 novel OCT derivatives. These compounds were subjected to in silico screening to predict their membrane permeation. Testing against nosocomial bacterial strains (G+ and G-) and their biofilms revealed that most compounds were highly effective against G+ bacteria, while compounds 7, 8, and 10-12 were effective against G- bacteria. Notably, compounds 6-8 were significantly more effective than OCT and BAC standards across the bacterial panel. Compound 12 stood out due to its low cytotoxicity and broad-spectrum antimicrobial activity, comparable to OCT. It also demonstrated impressive antifungal activity. Compound 1 was highly selective to fungi and four times more effective than OCT without its cytotoxicity. Several compounds, including 4, 6, 8, 9, 10, and 12, showed strong virucidal activity against murine cytomegalovirus and herpes simplex virus 1. In conclusion, these gemini QACs, especially compound 12, offer a promising alternative to current disinfectants, addressing emerging resistances with their enhanced antimicrobial, antifungal, and virucidal properties.

Bushy-Tailed QACs: The Development of Multicationic Quaternary Ammonium Compounds with a High Degree of Alkyl Chain Substitution

Quaternary ammonium compounds have served as a first line of protection for human health as surface disinfectants and sanitizers for nearly a century. However, increasing levels of bacterial resistance have spurred the development of novel QAC architectures. In light of the observed reduction in eukaryotic cell toxicity when the alkyl chains on QACs are shorter in nature (≤10 C), we prepared 47 QAC architectures that bear multiple short alkyl chains appended to up to three cationic groups, thus rendering them "bushy-tailed" multiQACs. Antibacterial activity was strong (often ~1-4 μM) in a varied set of bushy-tailed architectures, though observed therapeutic indices were not significantly improved over QAC structures bearing fewer and longer alkyl chains.

Chimeric Amphiphilic Disinfectants: Quaternary Ammonium/Quaternary Phosphonium Hybrid Structures

Cationic biocides play a crucial role in the disinfection of domestic and healthcare surfaces. Due to the rise of bacterial resistance towards common cationic disinfectants like quaternary ammonium compounds (QACs), the development of novel actives is necessary for effective infection prevention and control. Toward this end, a series of 15 chimeric biscationic amphiphilic compounds, bearing both ammonium and phosphonium residues, were prepared to probe the structure and efficacy of mixed cationic ammonium-phosphonium structures. Compounds were obtained in two steps and good yields, with straightforward and chromatography-free purifications. Antibacterial activity evaluation of these compounds against a panel of seven bacterial strains, including two MRSA strains as well as opportunistic pathogen A. baumannii, were encouraging, as low micromolar inhibitory activity was observed for multiple structures. Alkyl chain length on the ammonium group was, as expected, a major determinant of bioactivity. In addition, high therapeutic indexes (up to 125-fold) for triphenyl phosphonium-bearing amphiphiles were observed when comparing antimicrobial activity to mammalian cell lysis activity.

Pillararenes: a new frontier in antimicrobial therapy

Pillararenes have gained great interest among researchers in many fields due to their symmetric structure and facile functionalization. In this review, we summarize recent progress for pillararenes as antimicrobial agents, ranging from cationic pillararenes and peptide-modified pillararenes to sugar-functionalized pillararenes. Moreover, their structure-activity relationships are presented, and their mechanisms of action are discussed. As a state-of-the-art technology, their opportunities and outlook are also outlined in this emerging field. Overall, their potent inhibitory activity and high biocompatibility give them potential for the development of novel antimicrobial agents.

Exploring the Correlation of Dynamic Surface Tension with Antimicrobial Activities of Quaternary Ammonium-Based Disinfectants

Quaternary ammonium compound (QAC) disinfectants represent one of our first lines of defense against pathogens. Their inhibitory and bactericidal activities are usually tested through minimum inhibitory concentration (MIC) and time-kill assays, but these assays can become cumbersome when screening many compounds. We investigated how the dynamic surface tension (DST) measurements of QACs correlate with these antimicrobial activities by testing a panel of potent and structurally varied QACs against the gram-positive Staphylococcus aureus and the gram-negative Pseudomonas aeruginosa. We found that DST values correlated well with bactericidal activity in real-world disinfection conditions but not with MIC values. Moreover, no correlation between these two antimicrobial activities of QACs (bactericidal and inhibition) was observed. In addition, we observed that the bactericidal activity of our QAC panel against the gram-negative P. aeruginosa was severely affected in the presence of hard water. Interestingly, we found that the counterion of the QAC affects the killing of bacteria in these conditions, a phenomenon not observed in most MIC assessments. Moreover, some of our best-in-class QACs show enhanced bactericidal activity when combined with a commercially available QAC. In conclusion, we determined that an intrinsic physical property of QACs (DST) can be used as a technique to screen for bactericidal activity of QACs in conditions that mimic real-world disinfection conditions.

Chlorination of Pseudomonas aeruginosa in potable water

The present study examined the effects of chlorine (NaOCl) disinfection on Pseudomonas aeruginosa in potable water. The adhesion of the bacteria on glass surfaces and the growth of the adherent cells were measured after treatment with chlorine (0, 0.25, 0.5, 0.75, and 1 mg/L). Adhesion was assessed by optical microscopy, and cultivability of the adherent cells was estimated by counting the bacteria on solid medium after being recovered from the support surface. Regardless of the concentration applied, P. aeruginosa did not lose the ability to adhere or grow after adhesion. However, the two factors were influenced by the chlorine treatments. The results showed that the adhesive capacity and cultivability of adherent cells were linked. The maximum inhibition of adherence and cultivability was observed in the 0.25 and 0.5 mg/L treatments. At 0.75 and 1 mg/L, the adhesive capability and post-adhesive cultivability were slightly increased. The results suggest that residual concentrations of sodium hypochlorite fixed by standards (less than 1 mg/L) may be ineffective against P. aeruginosa, and thus could have an impact on consumers.

Alcohol-free synthesis, biological assessment, in vivo toxicological evaluation, and in silico analysis of novel silane quaternary ammonium compounds differing in structure and chain length as promising disinfectants

Quaternary ammonium compounds (QACs) are commonly used as disinfectants for industrial, medical, and residential applications. However, adverse health outcomes have been reported. Therefore, biocompatible disinfectants must be developed to reduce these adverse effects. In this context, QACs with various alkyl chain lengths (C12-C18) were synthesized by reacting QACs with the counterion silane. The antimicrobial activities of the novel compounds against four strains of microorganisms were assessed. Several in vivo assays were conducted on Drosophila melanogaster to determine the toxicological outcomes of Si-QACs, followed by computational analyses (molecular docking, simulation, and prediction of skin sensitization). The in vivo results were combined using a cheminformatics approach to understand the descriptors responsible for the safety of Si-QAC. Si-QAC-2 was active against all tested bacteria, with minimal inhibitory concentrations ranging from 13.65 to 436.74 ppm. Drosophila exposed to Si-QAC-2 have moderate-to-low toxicological outcomes. The molecular weight, hydrophobicity/lipophilicity, and electron diffraction properties were identified as crucial descriptors for ensuring the safety of the Si-QACs. Furthermore, Si-QAC-2 exhibited good stability and notable antiviral potential with no signs of skin sensitization. Overall, Si-QAC-2 (C14) has the potential to be a novel disinfectant.

Antimicrobial Tolerance in Salmonella: Contributions to Survival and Persistence in Processing Environments

Salmonella remains a top bacterial pathogen implicated in several food-borne outbreaks, despite the use of antimicrobials and sanitizers during production and processing. While these chemicals have been effective, Salmonella has shown the ability to survive and persist in poultry processing environments. This can be credited to its microbial ability to adapt and develop/acquire tolerance and/or resistance to different antimicrobial agents including oxidizers, acids (organic and inorganic), phenols, and surfactants. Moreover, there are several factors in processing environments that can limit the efficacy of these antimicrobials, thus allowing survival and persistence. This mini-review examines the antimicrobial activity of common disinfectants/sanitizers used in poultry processing environments and the ability of Salmonella to respond with innate or acquired tolerance and survive exposure to persists in such environments. Instead of relying on a single antimicrobial agent, the right combination of different disinfectants needs to be developed to target multiple pathways within Salmonella.

Anticancer and Antiphytopathogenic Activity of Fluorinated Isatins and Their Water-Soluble Hydrazone Derivatives

A series of new fluorinated 1-benzylisatins was synthesized in high yields via a simple one-pot procedure in order to explore the possible effect of ortho-fluoro (3a), chloro (3b), or bis-fluoro (3d) substitution on the biological activity of this pharmacophore. Furthermore, the new isatins could be converted into water-soluble isatin-3-hydrazones using their acid-catalyzed reaction with Girard's reagent P and its dimethyl analog. The cytotoxic action of these substances is associated with the induction of apoptosis caused by mitochondrial membrane dissipation and stimulated reactive oxygen species production in tumor cells. In addition, compounds 3a and 3b exhibit platelet antiaggregation activity at the level of acetylsalicylic acid, and the whole series of fluorine-containing isatins does not adversely affect the hemostasis system as a whole. Among the new water-soluble pyridinium isatin-3-acylhydrazones, compounds 7c and 5c,e exhibit the highest antagonistic effect against phytopathogens of bacterial and fungal origin and can be considered useful leads for combating plant diseases.

Biocidal and antibiofilm activities of arginine-based surfactants against Candida isolates

Amino-acid-based surfactants are a group of compounds that resemble natural amphiphiles and thus are expected to have a low impact on the environment, owing to either the mode of surfactant production or its means of disposal. Within this context, arginine-based tensioactives have gained particular interest, since their cationic nature-in combination with their amphiphilic character-enables them to act as broad-spectrum biocides. This capability is based mainly on their interactive affinity for the microbial envelope that alters the latter's structure and ultimately its function. In the work reported here, we investigated the efficiency of Nα-benzoyl arginine decyl- and dodecylamide against Candida spp. to further our understanding of the antifungal mechanism involved. For the assays, both a Candida albicans and a Candida tropicalis clinical isolates along with a C. albicans-collection strain were used as references. As expected, both arginine-based compounds proved to be effective against the strains tested through inhibiting both the planktonic and the sessile growth. Furthermore, atomic force microscopy techniques and lipid monolayer experiments enabled us to gain insight into the effect of the surfactant on the cellular envelope. The results demonstrated that all the yeasts treated exhibited changes in their exomorphologic structure, with respect to alterations in both roughness and stiffness, relative to the nontreated ones. This finding-in addition to the amphiphiles' proven ability to insert themselves within this model fungal membrane-could explain the changes in the yeast-membrane permeability that could be linked to viability loss and mixed-vesicle release.

Prevention of horizontal transfer of laboratory plasmids to environmental bacteria: comparison of the effectiveness of a few disinfection approaches to degrade DNA

The routine work of any molecular biology laboratory includes the daily use of microorganisms, including strains of E. coli, transformed with a variety of plasmids expressing at least one antibiotic resistance gene (ARG). Therefore, to avoid the accidental release of ARGs into environmental water, methods for disinfection of liquid laboratory waste must be effective in destroying nucleic acids. In support of this recommendation, the origin of replication of Enterobacteriaceae plasmids has been detected in strains of non-Enterobacteriaceae bacteria isolated from wastewater from laboratories and research institutes, suggesting that interspecific transfer of laboratory plasmids had occurred. Using quantitative polymerase chain reaction, we determined the decimal reduction value (D value, expressed as concentration of disinfectant or length of physical treatment) of several decontamination methods for their DNA degradation effect on cultures of E. coli Top10 transformed with a kanamycin resistant plasmid (pET28A + or pEGFP-C2). The estimated D values were 0.7 M for sulfuric acid, 6.3% for a commercial P3 disinfectant, 25 min for steam sterilization at 121 °C, and 49 min for disinfection by UVC. A 20-min treatment of bacteria cultures with a final concentration of 1-10% sodium hypochlorite was found to be ineffective in completely destroying a bacteria plasmid gene marker (coding for the pBR322 origin of replication). Residual DNA from NaClO-treated cells was 60%, while it decreased under 10% using the commercial disinfectant P3 diluted at 5%. As the degradation was incomplete in both cases, we recommend avoiding discharge of disinfected liquid waste to wastewater (even after chemical neutralization) without additional plasmid destruction treatment, to prevent horizontal transfer of laboratory ARGs to environmental bacteria.

Mechanisms of Listeria monocytogenes Disinfection with Benzalkonium Chloride: From Molecular Dynamics to Kinetics of Time-Kill Curves

Unravelling the mechanisms of action of disinfectants is essential to optimise dosing regimes and minimise the emergence of antimicrobial resistance. In this work, we examined the mechanisms of action of a commonly used disinfectant-benzalkonium chloride (BAC)-over a significant pathogen-L. monocytogenes-in the food industry. For that purpose, we used modelling at multiple scales, from the cell membrane to cell population inactivation. Molecular modelling revealed that the integration of the BAC into the membrane requires three phases: (1) the approaching of BAC to the cellular membrane, (2) the absorption of BAC to its surface, and (3) the integration of the compound into the lipid bilayer, where it remains at least for several nanoseconds, probably destabilising the membrane. We hypothesised that the equilibrium of adsorption, although fast, was limiting for sufficiently large BAC concentrations, and a kinetic model was derived to describe time-kill curves of a large population of cells. The model was tested and validated with time series data of free BAC decay and time-kill curves of L. monocytogenes at different inocula and BAC dose concentrations. The knowledge gained from the molecular simulation plus the proposed kinetic model offers the means to design novel disinfection processes rationally.

The responses of microbial metabolic activity, bacterial community and resistance genes under the coexistence of nanoplastics and quaternary ammonium compounds in the sewage environment

Nanoplastics (NPs) and quaternary ammonium compounds (QACs) are frequently detected in sewage. However, little is known about the risks of coexistence of NPs and QACs. In this study, the responses of microbial metabolic activity, bacterial community and resistance genes (RGs) to the exposure of polyethylene (PE), polylactic acid (PLA), silicon dioxide (SiO₂) and dodecyl dimethyl benzyl ammonium chloride (DDBAC) were focused on 2nd and 30th day of incubation in sewer environment. Bacterial community contributed 25.01 % to shape RGs and mobile genetic elements (MGEs) after two days of incubation in sewage and plastisphere. After 30 days of incubation, the most important individual factor (35.82 %) was turned to microbial metabolic activity. The metabolic capacity of the microbial communities in plastisphere was stronger than that from SiO₂ samples. Moreover, DDBAC inhibited the metabolic capacity of microorganisms in sewage samples, and increased the absolute abundances of 16S rRNA in plastisphere and sewage samples which might be similar to the hormesis effect. After 30 days of incubation, Aquabacterium was the predominant genus in plastisphere. As for SiO₂ samples, Brevundimonas was the predominant genus. QACs RGs (qacEdelta1-01, qacEdelta1-02) and antibiotic RGs (ARGs) (aac(6')-Ib, tetG-1) significantly enriched in plastisphere. There was also co-selection among qacEdelta1-01, qacEdelta1-02 and ARGs. In addition, VadinBC27 which enriched in plastisphere of PLA NPs was positively correlated with the potentially disease-causing genus Pseudomonas. It showed that after 30 days of incubation, plastisphere had an important effect on distribution and transfer of pathogenic bacteria and RGs. Plastisphere of PLA NPs also carried the risk of spreading disease.

The Antimicrobial and Antibiofilm Potential of New Water-Soluble Tris-Quaternary Ammonium Compounds

The invention and innovation of highly effective antimicrobials are always crucial tasks for medical and organic chemistry, especially at the current time, when there is a serious threat of shortages of effective antimicrobials following the pandemic. In the study presented in this article, we established a new approach to synthesizing three novel series of bioactive water-soluble tris-quaternary ammonium compounds using an optimized one-pot method, and we assessed their antimicrobial and antibiofilm potential. Five pathogenic microorganisms of the ESKAPE group, including highly resistant clinical isolates, were used as the test samples. Moreover, we highlighted the dependence of antibacterial activity from the hydrophilic-hydrophobic balance of the QACs and noted the significant performance of the desired products on biofilms with MBEC as low as 16 mg/L against bacteria and 8 mg/L against fungi. Particularly notable was the high activity against Pseudomonas aeruginosa and Acinetobacter baumannii, which are among the most resilient bacteria known. The presented work will provide useful insights for future research on the topic.

A review of Spaulding's classification system for effective cleaning, disinfection and sterilization of reusable medical devices: Viewed through a modern-day lens that will inform and enable future sustainability

Despite advances in medicine and innovations in many underpinning fields including disease prevention and control, the Spaulding classification system, originally proposed in 1957, remains widely used for defining the disinfection and sterilization of contaminated re-usable medical devices and surgical instruments. Screening PubMed and Scopus databases using a PRISMA guiding framework generated 272 relevant publications that were used in this review. Findings revealed that there is a need to evolve how medical devices are designed, and processed by cleaning, disinfection (and/or sterilization) to mitigate patient risks, including acquiring an infection. This Spaulding Classification remains in use as it is logical, easily applied and understood by users (microbiologists, epidemiologists, manufacturers, industry) and by regulators. However, substantial changes have occurred over the past 65 years that challenge interpretation and application of this system that includes inter alia emergence of new pathogens (viruses, mycobacteria, protozoa, fungi), a greater understanding of innate and adaptive microbial tolerance to disinfection, toxicity risks, increased number of vulnerable patients and associated patient procedures, and greater complexity in design and use of medical devices. Common cited examples include endoscopes that enable non- or minimal invasive procedures but are highly sophisticated with various types of materials (polymers, electronic components etc), long narrow channels, right angle and heat-sensitive components and various accessories (e.g., values) that can be contaminated with high levels of microbial bioburden and patient tissues after use. Contaminated flexible duodenoscopes have been a source of several significant infection outbreaks, where at least 9 reported cases were caused by multidrug resistant organisms [MDROs] with no obvious breach in processing detected. Despite this, there is evidence of the lack of attention to cleaning and maintenance of these devices and associated equipment. Over the last few decades there is increasing genomic evidence of innate and adaptive resistance to chemical disinfectant methods along with adaptive tolerance to environmental stresses. To reduce these risks, it has been proposed to elevate classification of higher-risk flexible endoscopes (such as duodenoscopes) from semi-critical [contact with mucous membrane and intact skin] to critical use [contact with sterile tissue and blood] that entails a transition to using low-temperature sterilization modalities instead of routinely using high-level disinfection; thus, increasing the margin of safety for endoscope processing. This timely review addresses important issues surrounding use of the Spaulding classification system to meet modern-day needs. It specifically addresses the need for automated, robust cleaning and drying methods combined with using real-time monitoring of device processing. There is a need to understand entire end-to-end processing of devices instead of adopting silo approaches that in the future will be informed by artificial intelligence and deep-learning/machine learning. For example, combinational solutions that address the formation of complex biofilms that harbour pathogenic and opportunistic microorganisms on the surfaces of processed devices. Emerging trends are addressed including future sustainability for the medical devices sector that can be enabled via a new Quintuple Helix Hub approach that combines academia, industry, healthcare, regulators, and society to unlock real world solutions.

Double BAC and Triple BAC: A Systematic Analysis of the Disinfectant Properties of Multicationic Derivatives of Benzalkonium Chloride (BAC)

Over the past decades, the shortcomings of established quaternary ammonium disinfectants have become increasingly clear. Although benzalkonium chloride (BAC) has enjoyed nearly a century of significantly protecting human health through surgical preparation, home use, and industrial applications, increasing levels of bacterial resistance have rendered it decreasingly effective. In light of more recent efforts that have informed us that multicationic amphiphilic disinfectants show both higher activity as well as diminished susceptibility to resistance, we embarked on the preparation of 27 multicationic QACs in an attempt to clearly document structure-activity relationships of next-generation BAC structures. Select biscationic BAC derivatives demonstrate single-digit micromolar activity against all seven bacteria tested and MIC values of 2- to 32-fold better than BAC. Particularly notable is the improvement against the more concerning bacteria like Acinetobacter baumannii and Pseudomonas aeruginosa, which pose a modern threat to legacy disinfectants like BAC. With simple synthetic paths, consistently high yields (averaging ∼80 %), and strong biological activity, potent structures with clear SAR trends and strong therapeutic indices have been established.

Soft QPCs: Biscationic Quaternary Phosphonium Compounds as Soft Antimicrobial Agents

Quaternary ammonium compounds (QACs) serve as a first line of defense against infectious pathogens. As resistance to QACs emerges in the environment, the development of next-generation disinfectants is of utmost priority for human health. Balancing antibacterial potency with environmental considerations is required to effectively counter the development of bacterial resistance. To address this challenge, a series of 14 novel biscationic quaternary phosphonium compounds (bisQPCs) have been prepared as amphiphilic disinfectants through straightforward, high-yielding alkylation reactions. These compounds feature decomposable or "soft" amide moieties in their side chains, anticipated to promote decomposition under environmental conditions. Strong bioactivity against a panel of seven bacterial pathogens was observed, highlighted by single-digit micromolar activity for compounds P6P-12A,12A and P3P-12A,12A. Hydrolysis experiments in pure water and in buffers of varying pH revealed surprising decomposition of the soft QPCs under basic conditions at the phosphonium center, leading to inactive phosphine oxide products; QPC stability (>24 h) was maintained in neutral solutions. The results of this work unveil soft QPCs as a potent and environmentally conscious new class of bisQPC disinfectants.

A Dicationic BODIPY-Based Fluorescent Bactericide to Combat Infectious Diseases and to Eradicate Bacterial Biofilms

Increased bacterial resistance against extensively used common disinfectants has begun to emerge. The discovery of disinfectants substituting the current commercially available ones is strongly needed. For this purpose, a dicationic BODIPY-based fluorescent amphiphile has been synthesized by specific molecular design. This quaternized BODIPY behaves as a broad-spectrum disinfectant against both Gram-positive and Gram-negative bacteria strains. It exhibits potent antimicrobial activity against tested microorganisms when compared with structurally similar disinfectant benzalkonium chloride (BAC). Moreover, it shows antibiofilm activity against Staphylococcus epidermidis with a minimum biofilm eradication concentration as low as 16 μg/mL. The interaction of this compound with the bacterial cell and genomic DNA was further evaluated by fluorescence spectroscopy and microscopy to follow cell internationalization and to clarify the mechanism of antibacterial action.

From Antibacterial to Antibiofilm Targeting: An Emerging Paradigm Shift in the Development of Quaternary Ammonium Compounds (QACs)

In a previous development stage, mostly individual antibacterial activity was a target in the optimization of biologically active compounds and antiseptic agents. Although this targeting is still valuable, a new trend has appeared since the discovery of superhigh resistance of bacterial cells upon their aggregation into groups. Indeed, it is now well established that the great majority of pathogenic germs are found in the environment as surface-associated microbial communities called biofilms. The protective properties of biofilms and microbial resistance, even to high concentrations of biocides, cause many chronic infections in medical settings and lead to serious economic losses in various areas. A paradigm shift from individual bacterial targeting to also affecting more complex cellular frameworks is taking place and involves multiple strategies for combating biofilms with compounds that are effective at different stages of microbiome formation. Quaternary ammonium compounds (QACs) play a key role in many of these treatments and prophylactic techniques on the basis of both the use of individual antibacterial agents and combination technologies. In this review, we summarize the literature data on the effectiveness of using commercially available and newly synthesized QACs, as well as synergistic treatment techniques based on them. As an important focus, techniques for developing and applying antimicrobial coatings that prevent the formation of biofilms on various surfaces over time are discussed. The information analyzed in this review will be useful to researchers and engineers working in many fields, including the development of a new generation of applied materials; understanding biofilm surface growth; and conducting research in medical, pharmaceutical, and materials sciences. Although regular studies of antibacterial activity are still widely conducted, a promising new trend is also to evaluate antibiofilm activity in a comprehensive study in order to meet the current requirements for the development of highly needed practical applications.

Effect of cetyltrimethylammonium chloride on various Escherichia coli strains and their inactivation kinetics by ozone and monochloramine

Cethyltrimethylammonium chloride (CTMA) is one of the most used quaternary ammonium compounds (QACs) in consumer products. CTMA and other QACs are only partially eliminated in municipal wastewater treatment and they can interact with bacteria in biological processes. Currently, there is only limited information on the antimicrobial efficiency of CTMA in matrices other than standard growth media and if and how CTMA influences conventional chemical disinfection. The results obtained in this study showed that the susceptibility of E. coli to CTMA was significantly enhanced in phosphate-buffered saline, lake water and wastewater compared to broth. In broth, a minimum inhibitory concentration (MIC) of CTMA of 20 mgL^-1 was observed for E. coli, whereas a 4-log inactivation occurred for CTMA concentrations of about 4 mgL^-1 in buffered ultra-purified water, a lake water and wastewater effluent. The impacts of the pre-exposure and the presence of CTMA on inactivation by ozone and monochloramine were tested with three different E. coli strains: AG100 with the efflux pump acrAB intact, AG100A with it deleted and AG100tet with it overexpressed. Pre-exposure of E. coli AG100 to CTMA led to an increased susceptibility for ozone with second-order inactivation rate constants (∼ 10⁶ M^-1s^-1) increasing by a factor of about 1.5. An opposite trend was observed for monochloramine with second-order inactivation rate constants (∼ 10³ M^-1s^-1) decreasing by a factor of about 2. For E. coli AG100tet, the second-order inactivation rate constant decreased by a factor of almost 2 and increased by a factor of about 1.5 for ozone and monochloramine, respectively, relative to the strain AG100. The simultaneous presence of CTMA and ozone enhanced the second-order inactivation rate constants for CTMA concentrations of 2.5 mgL^-1 by a factor of about 3. For monochloramine also an enhancement of the inactivation was observed, which was at least additive but might also be synergistic. Enhancement by factors from about 2 to 4.5 were observed for CTMA concentrations > 2.5 mgL^-1.

Rigidity-Activity Relationships of bisQPC Scaffolds Against Pathogenic Bacteria

Biscationic quaternary phosphonium compounds (bisQPCs) represent a promising class of antimicrobials, displaying potent activity against both Gram-negative and Gram-positive bacteria. In this study, we explored the effects of structural rigidity on the antimicrobial activity of QPC structures bearing a two-carbon linker between phosphonium groups, testing against a panel of six bacteria, including multiple strains harboring known disinfectant resistance mechanisms. Using simple alkylation reactions, 21 novel compounds were prepared, although alkene isomerization as well as an alkyne reduction were observed during the respective syntheses. The resulting bisQPC compounds showed strong biological activity, but were hampered by diminished solubility of their iodide salts. One compound (P2P-10,10 I) showed single digit micromolar activity against the entire panel of bacteria. Overall, intriguing biological activity was observed, with more rigid structures displaying better efficacy against Gram-negative strains and less rigid structures demonstrating slightly increased efficacy against S. aureus strains.

Combining microscopy assays of bacteria-surface interactions to better evaluate antimicrobial polymer coatings

Validation of the antimicrobial performance of contact-killing polymer surfaces through experimental determination of bacterial adhesion or viability is essential for their targeted development and application. However, there is not yet a consensus on a single most appropriate evaluation method or procedure. Combining and benchmarking previously reported assays could reduce the significant variation and misinterpretation of efficacy data obtained from different methods. In this work, we systematically investigated the response of bacteria cells to anti-adhesive and antiseptic polymer coatings by combining (i) bulk solution-based, (ii) thin-film spacer-based and (iii) direct contact assays. In addition, we evaluated the studied assays using a five-point scoring framework that highlights key areas for improvement. Our data suggest that combined microscopy assays provide a more comprehensive representation of antimicrobial performance, thereby helping to identify effective types of antibacterial polymer coatings. Importance We present and evaluate a combination of methods for validating the efficacy of antimicrobial surfaces. Antimicrobial surfaces/coatings based on contact-killing components can be instrumental to functionalise a wide range of products. However, there is not yet a consensus on a single, most appropriate method to evaluate their performance. By combining three microscopy methods, we were able to discern contact killing effects at the single cell level that were not detectable by conventional bulk microbiological analyses. The developed approach is considered advantageous for the future targeted development of robust and sustainable antimicrobial surfaces.

Isatin-3-acylhydrazones with enhanced lipophilicity: synthesis, antimicrobial activity evaluation and the influence on hemostasis system

Water-soluble trialkylammonium isatin-3-hydrazone derivatives bearing hydroxybenzyl substituent were easily synthesized with high yields. XRD studies confirmed the presence of these compounds as trans-( Z )-isomers in a crystal. It was shown that an increase in the lipophilicity of the cationic center leads to an increase in activity against Gram-positive bacteria Staphylococcus aureus and Bacillus cereus, including methicillin-resistant (MRSA) strains. The MIC values of the leading compounds turned out to be 2-100 times higher than the MIC of norfloxacin against the MRSA strains in the absence of hemo- and cytotoxicity. Antiaggregation and anticoagulation properties were in vitro better than for acetylsalicylic acid and sodium heparin drugs. It has been shown by UV spectroscopy and fluorescence microscopy that the mechanism of antimicrobial action of new acylhydrazones is associated with their ability to destroy the bacterial cell membrane.

Sustainable triazine-derived quaternary ammonium salts as antimicrobial agents

The first examples of highly efficient antimicrobial triazine-derived bis imidazolium quaternary ammonium salts (TQAS) are reported. TQAS have been prepared with an easy, atom efficient, economically sustainable strategy and tested as antimicrobial agents, reaching MIC values below 10 mg L^-1. Distinctively, TQAS have low MIC and low cytotoxicity.

Chlorine disinfectants promote microbial resistance in Pseudomonas sp

The substantial use of disinfectants has increased antibiotic resistance, thereby mediating serious ecological safety issues worldwide. Accumulating studies have reported the role of chlorine disinfectants in promoting disinfectant resistance. The present study sought to investigate the role of chlorine disinfectants in developing multiple resistance in Pseudomonas sp. isolated from the river through antioxidant enzyme measurement, global transcriptional analyses, Gene Ontology (GO), and the Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis. The results demonstrated that 100 mg/L sodium hypochlorite could increase disinfectant resistance and antibiotic resistance. The SOS response (a conserved response to DNA damage) triggered by oxidative stress makes bacteria resistant to chlorine. An increase in antibiotic resistance could be attributed to a decreased membrane permeability, increased expression of MuxABC-OpmB efflux pump, beta-lactamase, and antioxidant enzymes. Additionally, KEGG enrichment analysis suggested that the differentially expressed genes were highly enriched in the metabolic pathways. In summary, the study results revealed the impact of chlorine disinfectants in promoting microbial disinfectant resistance and antibiotic resistance. This study will provide insight into disinfectant resistance mechanisms.

Novel Phenyl-Based Bis-quaternary Ammonium Compounds as Broad-Spectrum Biocides

Herein we report the synthesis and microbiological evaluation of novel phenyl based bis-quaternary ammonium compounds (bis-QACs). Using a simple 2-step synthetic route from dibromo- and dihydroxybenzenes, we obtained a structurally diverse broad panel of bis-QACs with topologically distinct bridging connections between pyridinium heads. Selected analogs possessed potent broad-spectrum biocidal activity against both bacterial and fungal pathogens: methicillin-resistant Staphylococcus aureus (ATCC 43300); Escherichia coli (ATCC 25922), Klebsiella pneumonia (ATCC 700603), Acinetobacter baumannii (ATCC 19606), Pseudomonas aeruginosa (ATCC 27853), Candida albicans (ATCC 90028), Cryptococcus neoformans var. grubii (ATCC 208821). Promising compounds displayed minimum inhibitory concentrations (MIC) values ≤0.25 μg/mL alongside improved cytotoxicity and hemolytic profiles compared to modern antiseptics. Thus, synthesized bis-QACs represent a promising class of biocides with the potential to replace existing household sanitizers.

Quaternary Ammonium Compounds (QACs) and Ionic Liquids (ILs) as Biocides: From Simple Antiseptics to Tunable Antimicrobials

Quaternary ammonium compounds (QACs) belong to a well-known class of cationic biocides with a broad spectrum of antimicrobial activity. They are used as essential components in surfactants, personal hygiene products, cosmetics, softeners, dyes, biological dyes, antiseptics, and disinfectants. Simple but varied in their structure, QACs are divided into several subclasses: Mono-, bis-, multi-, and poly-derivatives. Since the beginning of the 20th century, a significant amount of work has been dedicated to the advancement of this class of biocides. Thus, more than 700 articles on QACs were published only in 2020, according to the modern literature. The structural variability and diverse biological activity of ionic liquids (ILs) make them highly prospective for developing new types of biocides. QACs and ILs bear a common key element in the molecular structure-quaternary positively charged nitrogen atoms within a cyclic or acyclic structural framework. The state-of-the-art research level and paramount demand in modern society recall the rapid development of a new generation of tunable antimicrobials. This review focuses on the main QACs exhibiting antimicrobial and antifungal properties, commercial products based on QACs, and the latest discoveries in QACs and ILs connected with biocide development.

Back to Basics: Choosing the Appropriate Surface Disinfectant

From viruses to bacteria, our lives are filled with exposure to germs. In built environments, exposure to infectious microorganisms and their byproducts is clearly linked to human health. In the last year, public health emergency surrounding the COVID-19 pandemic stressed the importance of having good biosafety measures and practices. To prevent infection from spreading and to maintain the barrier, disinfection and hygiene habits are crucial, especially when the microorganism can persist and survive on surfaces. Contaminated surfaces are called fomites and on them, microorganisms can survive even for months. As a consequence, fomites serve as a second reservoir and transfer pathogens between hosts. The knowledge of microorganisms, type of surface, and antimicrobial agent is fundamental to develop the best approach to sanitize fomites and to obtain good disinfection levels. Hence, this review has the purpose to briefly describe the organisms, the kind of risk associated with them, and the main classes of antimicrobials for surfaces, to help choose the right approach to prevent exposure to pathogens.

The silent pandemic: Emergent antibiotic resistances following the global response to SARS-CoV-2

The ongoing SARS-CoV-2 pandemic has highlighted the importance of the rapid development of vaccines and antivirals. However, the potential for the emergence of antibiotic resistances due to the increased use of antibacterial cleaning products and therapeutics presents an additional, underreported threat. Most antibacterial cleaners contain simple quaternary ammonium compounds (QACs); however, these compounds are steadily becoming less effective as antibacterial agents. QACs are extensively used in SARS-CoV-2-related sanitization in clinical and household settings. Similarly, due to the danger of secondary infections, antibiotic therapeutics are increasingly used as a component of COVID-19 treatment regimens, even in the absence of a bacterial infection diagnosis. The increased use of antibacterial agents as cleaners and therapeutics is anticipated to lead to novel resistances in the coming years.

An Efficient Synthesis of 3-Alkylpyridine Alkaloids Enables Their Biological Evaluation

3-Alkylpyridine alkaloids (3-APAs) isolated from the arctic sponge Haliclona viscosa are a promising group of bioactive marine alkaloids. However, due to limited bioavailability, investigations of their bioactivity have been hampered. Additionally, synthesis of a common intermediate requires the use of protecting groups and harsh conditions. In this work, we developed a simple and concise two-step route to nine different natural and synthetic haliclocyclins. These compounds displayed modest antibiotic activity against several Gram-positive bacterial strains.

Trivalent sulfonium compounds (TSCs): Tetrahydrothiophene-based amphiphiles exhibit similar antimicrobial activity to analogous ammonium-based amphiphiles

Recent advances in the development of quaternary ammonium compounds (QACs) have focused on new structural motifs to increase bioactivity, but significantly less studied has been the change from ammonium- to sulfonium-based disinfectants. Herein, we report the synthesis of structurally analogous series of quaternary ammonium and trivalent sulfonium compounds (TSCs). The bioactivity profiles of these compounds generally mirror each other, and the antibacterial activity of sulfonium-based THT-18 was found to be comparable to the commercial disinfectant, BAC. The development of these compounds presents a new avenue for further study of disinfectants to combat the growing threat of bacterial resistance.

Design Guidelines for Cationic Pillar[n]arenes that Prevent Biofilm Formation by Gram-Positive Pathogens

Bacterial biofilms are a major threat to human health, causing persistent infections that lead to millions of fatalities worldwide every year. Biofilms also cause billions of dollars of damage annually by interfering with industrial processes. Recently, cationic pillararenes were found to be potent inhibitors of biofilm formation in Gram-positive bacteria. To identify the structural features of pillararenes that result in antibiofilm activity, we evaluated the activity of 16 cationic pillar[5]arene derivatives including that of the first cationic water-soluble pillar[5]arene-based rotaxane. Twelve of the derivatives were potent inhibitors of biofilm formation by Gram-positive pathogens. Structure activity analyses of our pillararene derivatives indicated that positively charged head groups are critical for the observed antibiofilm activity. Although certain changes in the lipophilicity of the substituents on the positively charged head groups are tolerated, dramatic elevation in the hydrophobicity of the substituents or an increase in steric bulk on these positive charges abolishes the antibiofilm activity. An increase in the overall positive charge from 10 to 20 did not affect the activity significantly, but pillararenes with 5 positive charges and 5 long alkyl chains had reduced activity. Surprisingly, the cavity of the pillar[n]arene is not essential for the observed activity, although the macrocyclic structure of the pillar[n]arene core, which facilitates the clustering of the positive charges, appears important. Interestingly, the compounds found to be efficient inhibitors of biofilm formation were nonhemolytic at concentrations that are ∼100-fold of their MBIC₅₀ (the minimal concentration of a compound at which at least 50% inhibition of biofilm formation was observed compared to untreated cells). The structure–activity relationship guidelines established here pave the way for a rational design of potent cationic pillar[n]arene-based antibiofilm agents.

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.

Metallocene QACs: The Incorporation of Ferrocene Moieties into monoQAC and bisQAC Structures

Inspired by the incorporation of metallocene functionalities into a variety of bioactive structures, particularly antimicrobial peptides, we endeavored to broaden the structural variety of quaternary ammonium compounds (QACs) by the incorporation of the ferrocene moiety. Accordingly, 23 ferrocene-containing mono- and bisQACs were prepared in high yields and tested for activity against a variety of bacteria, including Gram-negative strains and a panel of clinically isolated MRSA strains. Ferrocene QACs were shown to be effective antiseptics with some displaying single-digit micromolar activity against all bacteria tested, demonstrating yet another step in the expansion of structural variety of antiseptic QACs.

Advancements in the Development of Non-Nitrogen-Based Amphiphilic Antiseptics to Overcome Pathogenic Bacterial Resistance

The prevalence of quaternary ammonium compounds (QACs) as common disinfecting agents for the past century has led bacteria to develop resistance to such compounds. Given the alarming increase in resistant strains, new strategies are required to combat this rise in resistance. Recent efforts to probe and combat bacterial resistance have focused on studies of multiQACs. Relatively unexplored, however, have been changes to the primary atom bearing positive charge in these antiseptics. Here we review the current state of the field of both phosphonium and sulfonium amphiphilic antiseptics, both of which hold promise as novel means to address bacterial resistance.

Tricepyridinium-inspired QACs yield potent antimicrobials and provide insight into QAC resistance

Quaternary ammonium compounds (QACs) comprise a large class of surfactants, consumer products, and disinfectants. The recently-isolated QAC natural product tricepyridinium bromide displays potent inhibitory activity against S. aureus but due to its unique structure, its mechanism of action remains unclear. A concise synthetic route to access tricepyridinium analogs was thus designed and four N-alkyl compounds were generated in addition to the natural product. Biological analysis of these compounds revealed that they display remarkable selectivity towards clinically-relevant Gram-positive bacteria exceeding that of commercially-available QACs such as cetylpyridinium chloride (CPC) and benzalkonium chloride (BAC) while having little to no hemolytic activity. Molecular modeling studies revealed that tricepyridinium and shorter-chain N-alkyl analogs may preferentially bind to the QacR transcription factor leading to potential activation of the QAC resistance pathway found in MRSA; however, our newly synthesized analogs are able to overcome this liability.

Are Quaternary Ammonium Compounds, the Workhorse Disinfectants, Effective against Severe Acute Respiratory Syndrome-Coronavirus-2?

A novel virus named Severe Acute Respiratory Syndrome-Coronavirus-2 (SARS-CoV-2) emerged from Wuhan, China in late 2019. Since then, the virus has quickly spread worldwide, leading the World Health Organization to declare it as a pandemic; by the end of April 2020, the number of cases exceeded 3 million. Due to the high infectivity rate, SARS-CoV-2 is difficult to contain, making disinfectant protocols vital, especially for essential, highly trafficked areas such as hospitals, grocery stores, and delivery centers. According to the Centers for Disease Control and Prevention, best practices to slow the spread rely on good hand hygiene, including proper handwashing practices as well as the use of alcohol-based hand sanitizers. However, they provide warning against sanitizing products containing benzalkonium chloride (BAC), which has sparked concern in both the scientific community as well as the general public as BAC, a common quaternary ammonium compound (QAC), is ubiquitous in soaps and cleaning wipes as well as hospital sanitation kits. This viewpoint aims to highlight the outdated and incongruous data in the evaluation of BAC against the family of known coronaviruses and points to the need for further evaluation of the efficacy of QACs against coronaviruses.

Transporters and Efflux Pumps Are the Main Mechanisms Involved in Staphylococcus epidermidis Adaptation and Tolerance to Didecyldimethylammonium Chloride

Staphylococcus epidermidis cleanroom strains are often exposed to sub-inhibitory concentrations of disinfectants, including didecyldimethylammonium chloride (DDAC). Consequently, they can adapt or even become tolerant to them. RNA-sequencing was used to investigate adaptation and tolerance mechanisms of S. epidermidis cleanroom strains (SE11, SE18), with S. epidermidis SE11Ad adapted and S. epidermidis SE18To tolerant to DDAC. Adaptation to DDAC was identified with up-regulation of genes mainly involved in transport (thioredoxin reductase [pstS], the arsenic efflux pump [gene ID, SE0334], sugar phosphate antiporter [uhpT]), while down-regulation was seen for the Agr system (agrA, arC, agrD, psm, SE1543), for enhanced biofilm formation. Tolerance to DDAC revealed the up-regulation of genes associated with transporters (L-cysteine transport [tcyB]; uracil permease [SE0875]; multidrug transporter [lmrP]; arsenic efflux pump [arsB]); the down-regulation of genes involved in amino-acid biosynthesis (lysine [dapE]; histidine [hisA]; methionine [metC]), and an enzyme involved in peptidoglycan, and therefore cell wall modifications (alanine racemase [SE1079]). We show for the first time the differentially expressed genes in DDAC-adapted and DDAC-tolerant S. epidermidis strains, which highlight the complexity of the responses through the involvement of different mechanisms.