Concentrations Of Quaternary Ammonium Compounds Research Articles

A surface sampling and liquid chromatography mass spectrometry method for the analysis of quaternary ammonium compounds collected from public transportation buses in New Jersey

Quaternary ammonium compounds (QACs) are a class of antimicrobial disinfectants whose use in cleaning products increased during the COVID-19 pandemic. Chemically, their low vapor pressure indicates a proclivity to persist on surfaces, and their presence suggests a level of protection against microorganisms. The widespread application of QACs in response to the SARS CoV-2 virus created a need to evaluate their longevity on surfaces, for both efficacy and possible health risks. There are however, no standardized analytical methods for QAC surface sampling and analysis, and no published studies quantifying their concentrations on mass transportation vehicles-a high occupancy, close-contact microenvironment documented to facilitate the spread the SARS CoV-2 virus. Here, we describe a robust liquid chromatography mass spectrometry (LC-MS) method for the analysis of QACs and simultaneous development of a direct surface sampling and extraction protocol. We demonstrate the applicability of the method through the analysis of surface samples collected from in-service public transportation buses.The rapid, sensitive LC-MS method included 8 target QACs quantified on a Q-Exactive HF Hybrid Quadrupole-Orbitrap mass spectrometer using an electrospray ionization source and Dionex UltiMate 3000 UHPLC system for analyte separation. QAC standard mixtures at concentrations between 0.1 ng mL−1 and 2000 ng mL−1 were analyzed, and chromatographic separation of all analytes was achieved in less than 10 min. All correlation coefficients were reported at r > 0.986, and LODs ranged from 0.007 to 2.103 ng mL−1 for all compounds, confirming the method's sensitivity. A previously reported surface sampling and extraction protocol was modified to further simplify the procedure and expand the number of target compounds. The new sampling protocol was optimized from 10 commercially available wipes and 4 solvent types by quantifying recovery from the surface. Band-Aid brand small gauze pads saturated with isopropanol had the highest recovery efficiencies, ranging from 61.5 to 102.9% across all analytes. To test the real-world applicability, wipe samples were collected from 4 in-circulation New Jersey Transit buses on 5 separate days over the course of a month to assess the occurrence and longevity of QACs on sanitized mass transportation vehicles. Concentrations of QACs were detected on every wipe sample taken, and at all sampled time points, confirming their persistence on hard surfaces. QACs have the potential to form polymers, and detection of the polymer might serve as a secondary indication of their effectiveness on surfaces. None of the polymers detected however, were unique to QACs from this study. The polymers detected were already present in the wipe and used as an internal standard to demonstrate the efficacy of extraction and analysis of polymeric QACs.

Biological removal of benzalkonium chlorides from wastewater by immobilized cells of Pseudomonas sp. BIOMIG1 in an up-flow packed bed reactor

Quaternary ammonium compounds (QACs) are active ingredients of many disinfectants used against SARS-CoV-2 to control the transmission of the virus through human-contact surfaces. As a result, QAC consumption has increased more than twice during the pandemic. Consequently, the concentration of QACs in wastewater and receiving environments may increase. Due to their antimicrobial activity, high levels of QACs in wastewater may cause malfunctioning of biological treatment systems resulting in inadequate treatment of wastewater. In this study, a biocatalyst was produced by entrapping Pseudomonas sp. BIOMIG1 capable of degrading QACs in calcium alginate. Bioactive 3-mm alginate beads degraded benzalkonium chlorides (BACs), a group of QACs, with a rate of 0.47 µM-BACs/h in shake flasks. A bench-scale continuous up-flow reactor packed with BIOMIG1-beads was operated over one and a half months with either synthetic wastewater or secondary effluent containing 2–20 µM BACs at an empty bed contact time (EBCT) ranging between 0.6 and 4.7 h. Almost complete BAC removal was achieved from synthetic and real wastewater at and above 1.2 h EBCT without aeration and effluent recirculation. The microbial community in beads dominantly composed of BIOMIG1 with trace number of Achromobacter spp. after the operation of the reactor with the real wastewater, suggesting that BIOMIG1 over-competed native wastewater bacteria during the operation. This reactor system offers a low cost and robust treatment of QACs in wastewater. It can be integrated to conventional treatment systems for efficient removal of QACs from the wastewater, especially during the pandemic period.

Low-Level Tolerance to Fluoroquinolone Antibiotic Ciprofloxacin in QAC-Adapted Subpopulations of Listeria monocytogenes.

There was a development of low-level tolerance to fluoroquinolone antibiotic ciprofloxacin in Listeria monocytogenes after sublethal adaptation to quaternary ammonium compound (QAC). Using eight L. monocytogenes strains, we determined the changes in short-range MIC, growth rate, and survival for heterologous stress response to ciprofloxacin, after sublethal exposure to daily cycles of fixed or gradually increasing concentration of QAC. Three main findings were observed. (1) MIC increase—QAC-adapted subpopulations exhibited a significant increase in short-range MIC of ciprofloxacin, by 1.5 to 2.9 fold, as compared to non-adapted control for 4/8 strains (p < 0.05). (2) Growth rate increase—QAC-adapted subpopulations exhibited significant 2.1- to 6.8- fold increase in growth rate (OD600 at 10 h) in ciprofloxacin-containing broth, as compared to non-adapted control for 5/8 strains (p < 0.05). (3) Survival increase—QAC-adapted subpopulations of L. monocytogenes yielded significantly higher survival in ciprofloxacin-containing agar by 2.2 to 4.3 log CFU/mL for 4/8 strains, as compared to non-adapted control (p ˂ 0.05). However, for other 4/8 strains of L. monocytogenes, there was no increase in survival of QAC-adapted subpopulations, as compared to non-adapted control in ciprofloxacin. These findings suggest the potential formation of low-level ciprofloxacin-tolerant subpopulations in some L. monocytogenes strains when exposed to residual QAC concentrations (where QAC might be used widely) and such cells if not inactivated might create food safety risk.

Altered toxicological endpoints in humans from common quaternary ammonium compound disinfectant exposure.

This study found that 80 % of study participants contained QACs in their blood; and that markers of inflammation, mitochondrial function, and sterol homeostasis varied with blood QAC concentration.

Antiseptic quaternary ammonium compound tolerance by gram-negative bacteria can be rapidly detected using an impermeant fluorescent dye-based assay

Biocides such as quaternary ammonium compounds (QACs) are potentially important contributors towards bacterial antimicrobial resistance development, however, their contributions are unclear due to a lack of internationally recognized biocide testing standards. Methods to detect QAC tolerance are limited to laborious traditional antimicrobial susceptibility testing (AST) methods. Here, we developed a rapid fluorescent dye-based membrane impermeant assay (RFDMIA) to discriminate QAC susceptibility among Gram-negative Enterobacterales and Pseudomonadales species. RFDMIA uses a membrane impermeant fluorescent dye, propidium iodide, in a 30-min 96-well fluorescent microplate-based assay where cell suspensions are exposed to increasing QAC concentrations. Our results demonstrate that RFDMIA can discriminate between QAC-susceptible and QAC-adapted Escherichia coli tolerant phenotypes and predict benzalkonium and cetrimide tolerance in all species tested except for intrinsically fluorescent Pseudomonas aeruginosa. RFDMIA identified a close association to minimum inhibitory concentration values determined by broth microdilution AST and increasing fluorescent dye emission values. RFDMIA emission values and scanning electron microscopy results also suggest that CET-adapted E. coli isolates have a CET dependence, where cells require sub-inhibitory CET concentrations to maintain bacilliform cell integrity. Overall, this study generates a new, rapid, sensitive fluorescent assay capable of detecting QAC-susceptible Gram-negative bacteria phenotypes and cell membrane perturbations.

Comparison of three neutralizing broths for environmental sampling of low levels of Listeria monocytogenes desiccated on stainless steel surfaces and exposed to quaternary ammonium compounds

BackgroundAn effective environmental sampling method involves the use of a transport/neutralizing broth with the ability to neutralize sanitizer residues that are collected during sampling and to maintain viability of stressed Listeria monocytogenes (Lm) cells.ResultsWe applied Lm onto stainless steel surfaces and then subjected Lm to desiccation stress for 16–18 h at room temperature (RT, 21–24 °C). This was followed by the subsequent application of Whisper™ V, a quaternary ammonium compound (QAC)-based sanitizer, diluted to 400 ppm and 8000 ppm of active quat, for 6 h. We then sampled Lm with sponges pre-moistened in three transport broths, Dey/Engley (D/E) broth, Letheen broth and HiCap™ broth, to generate environmental samples that contained sanitizer residues and low levels of stressed Lm, which were subsequently analyzed by an enrichment-based method. This scheme conformed with validation guidelines of AOAC International by using 20 environmental test portions per broth that contained low levels of Lm such that not all test portions were positive (i.e., fractional positive). We showed that D/E broth, Letheen broth and HiCap™ broth performed similarly when no quat or 400 ppm of quat was applied to the Lm contaminating stainless steel surfaces. However, when 8000 ppm of quat was applied, Letheen broth did not effectively neutralize the QAC in the samples. These comparisons were performed on samples stored under three conditions after collection to replicate scenarios of sample transport, RT for 2 h, 4 °C for 24 h and 4 °C for 72 h. Comparisons under the three different scenarios generally reached the same conclusions. In addition, we further demonstrated that storing Letheen and HiCap™ broths at RT for two months before sampling did not reduce their capacity to neutralize sanitizers.ConclusionsWe developed a scheme to evaluate the ability of transport broths to neutralize QAC sanitizers. The three transport broths performed similarly with a commonly used concentration of quat, but Letheen broth could not effectively neutralize a very high concentration of QAC. The performance of transport broths was not significantly affected under the assessed pre-sampling and post-sampling storage conditions.

Soil water solutes reduce the critical micelle concentration of quaternary ammonium compounds

Quaternary alkyl ammonium compounds (QAACs) are produced in large quantities for use as surfactants and disinfectants and also found in soils, sediments, and surface waters, where they are potentially involved in the selection of antibiotic resistance genes. Micelle formation influences fate and effects of QAACs. The critical micelle concentration (CMC) of six homologs of benzylalkylammonium chlorides (BAC) was determined in deionized water, 0.01 M CaCl2 solution, and aqueous soil extracts, using both spectrofluorometric and tensiometric methods. Additionally, eight organic model compounds were employed at concentrations of 15 mg C L−1 as background solutes in order to test the effect of dissolved organic carbon (DOC) on CMCs. Results found CMCs decreased with an increasing length of the alkyl chain from 188 mM for BAC-C8 to 0.1 mM for BAC-C18. Both methods yielded similar results for measurements in water and CaCl2 solution; however, the spectrofluorescence method did not work for soil extracts due to fluorescence quenching phenomena. In soil extracts, CMCs of BAC-C12 were reduced below 3.7 mM, while the CMC reduction in soil extracts was less pronounced for BAC-C16. Besides ionic strength, molecular structures of BACs and dissolved organic compounds also affected the CMC. The number of carboxyl groups and small molecular weights of the DOC model compounds reduced the CMCs of BAC-C12 and BAC-C16 at pH 6. This study highlights that CMCs can be surpassed in soil solution, pore waters of sediments, or other natural waters even at (small) concentrations of QAACs typically found in the environment.

Pre-growth conditions and strain diversity affect nisin treatment efficacy against Listeria monocytogenes on cold-smoked salmon

Listeria monocytogenes is a human pathogen that is commonly found in environments associated with cold-smoked salmon. Nisin is a natural antimicrobial that can be used as a food preservative. While nisin is active against a number of Gram-positive bacteria, including L. monocytogenes, environmental stresses encountered in cold-smoked salmon processing facilities might affect L. monocytogenes' nisin susceptibility. The objective of this study was to investigate the effect of seafood-relevant pre-growth conditions and L. monocytogenes strain diversity on nisin treatment efficacy on cold-smoked salmon. Six L. monocytogenes strains representing serotypes most commonly associated with cold-smoked salmon (1/2a, 1/2b, and 4b) were initially pre-grown under a number of seafood-relevant conditions and challenged with nisin in growth media modified to represent the characteristics of cold-smoked salmon. The pre-growth conditions with the lowest mean log reduction due to nisin and the highest strain-to-strain variability were selected for experiments on cold-smoked salmon; these included: (i) 4.65% w.p. NaCl (“NaCl”); (ii) pH = 6.1 (“pH”); (iii) 0.5 μg/ml benzalkonium chloride (“Quat”); and a control (“BHI”). Cold-smoked salmon slices with or without nisin were inoculated with L. monocytogenes pre-grown in one of the conditions above, vacuum-packed, and incubated at 7 °C. L. monocytogenes were enumerated on days 1, 15, and 30. A linear mixed effects model was constructed to investigate the effect of pre-growth condition, day in storage, serotype, source of isolation as well as their interactions on nisin efficacy against L. monocytogenes. Compared to pre-growth in “BHI”, significant reduction (P < 0.05) in nisin efficacy was induced by pre-growth in “pH” and “Quat” on both days 15 and 30, and by pre-growth in “NaCl” on day 30, indicating a time-dependent cross-protection effect. Additionally, an effect of L. monocytogenes' serotype on the cross-protection to nisin was observed; pre-growth in “pH” significantly reduced nisin efficacy against serotype 1/2a and 4b strains, but not against 1/2b strains. In conclusion, pre-exposure to mildly acidic environment, high salt content, and sublethal concentrations of quaternary ammonium compounds, is likely to provide cross-protection against a subsequent nisin treatment of L. monocytogenes on cold-smoked salmon. Therefore, challenge studies that use pre-growth in “BHI”, as well as more susceptible L. monocytogenes strains, may overestimate the efficacy of nisin as a control strategy for cold-smoked salmon.

Distance-based paper device using polydiacetylene liposome as a chromogenic substance for rapid and in-field analysis of quaternary ammonium compounds.

This work presents an affordable distance-based microfluidic paper-based device (μPAD), using polydiacetylene (PDA) liposome as a chromogenic substance with a smartphone-based photo editor, for rapid and in-field analysis of quaternary ammonium compounds (QACs) (e.g., didecyldimethylammonium chloride (DDAC), benzyldimethyltetradecyl ammonium chloride (BAC), and cetylpyridinium chloride (CPC)). In-field analysis of these compounds is important to ensure their antimicrobial activity and user safety since they are widely utilized as disinfectants in households and hospitals. The μPAD featured a thermometer-like shape consisting of a sample reservoir and a microchannel as the detection zone, which was pre-deposited with PDA liposome. The color change from blue to red appeared in the presence of QACs and the color bar lengths were proportional to the QAC concentrations. Reactions of QACs with the PDA required a specific pH range (from pH4.0 to 10.0) and a readout time of 7min. Analytical performance characteristics of the device were tested with DDAC, BAC, and CPC showing acceptable specificity, accuracy (96.1-109.4%), and precision (%RSDs ≤ 9.3%). Limits of detection and quantitation were in the ranges of 20 to 80 and 70 to 250μM, respectively. Feasibility of the newly developed device was demonstrated for in-field analysis of QACs in fumigation solution providing comparable results with those obtained from a colorimetric assay (P > 0.05). The proposed device shows potentials for further applications of other analytes since it offers speed, simplicity, and affordability for in-field analysis, especially in remote areas where expertise, resources, and infrastructures are limited. Graphical abstract.

Adaptation of Pseudomonas aeruginosa to constant sub-inhibitory concentrations of quaternary ammonium compounds

The susceptibility profile of P. aeruginosa exposed to constant sub-inhibitory 3 concentrations of quaternary ammonium compounds was characterized as well as the 4 nanomechanical membrane properties.

The impact and mechanism of quaternary ammonium compounds on the transmission of antibiotic resistance genes.

The emergence of antibiotic resistance genes (ARGs) in microbes can be largely attributed to the abuse and misuse of antibiotics and biocides. Quaternary ammonium compounds (QACs) have been used worldwide as common disinfectants and detergents; however, their potential impact on the spread and diffusion of ARGs is still unknown. In this study, we detected the QAC resistance gene (qacEΔ1), the 1 integron gene (intI1), and 12 ARGs (sul1, sul2, cfr, cml, fexA, tetA, tetG, tetQ, tetX, ermB, blaTEM, and dfrA1) in 48 water samples from three watersheds by quantitative PCR (qPCR). We investigated the evolution of bacterial antibiotic resistance under QAC and antibiotic environmental pressures by long-term continuous culture. In addition, five QACs were selected to investigate the effect of QAC on the efficiency of conjugation transfer. The changes in bacterial cell membrane and production of reactive oxygen species (ROS) were detected by flow cytometry, revealing the mechanism by which QAC affects the spread of antibiotic resistance. Our results showed that the QAC resistance gene was ubiquitous in watersheds and it had significant correlation with intI1 and seven ARGs (r = 0.999, p < 0.01). QACs could increase the resistance of bacteria to multiple antibiotics. Furthermore, all five QACs promoted the conjugation transfer of the RP4 plasmid; the optimal concentration of QACs was about 10-1-10-2mg/L and their transfer efficiencies were between 1.33 × 10-6 and 8.87 × 10-5. QACs enhanced membrane permeability of bacterial cells and stimulated bacteria to produce ROS, which potentially promoted the transfer of plasmids between bacteria. In conclusion, this study demonstrated that QACs may facilitate the evolution and gene transfer of antibiotic resistance gene among microbiome.

Phytotoxicity and oxidative effects of typical quaternary ammonium compounds on wheat (Triticum aestivum L.) seedlings.

The large-scale use of quaternary ammonium compounds (QACs) in medicines or disinfectants can lead to their release into the environment, posing a potential risk to organisms. This study examined the effects of three typical QACs, dodecyltrimethylammonium chloride (DTAC), dodecyldimethylbenzylammonium chloride (DBAC), and didodecyldimethylammonium chloride (DDAC), on hydroponically cultured wheat seedlings. After 14days of exposure, both hormesis and phytotoxicity were observed in the wheat seedlings. The shoot and root fresh weight gradually increased as QAC concentrations rose from 0.05 to 0.8mgL-1. However, higher QAC concentrations severely inhibited plant growth by decreasing shoot and root fresh weight, total root length, and photosynthetic pigment content. Moreover, the increase in malondialdehyde and O2.- contents, as well as root membrane permeability, reflected an oxidative burst and membrane lipid peroxidation caused by QACs. However, the effects of QACs on the levels of these oxidative stress markers were compound-specific, and the changes in superoxide dismutase, peroxidases, and catalase activity were partly related to reactive oxygen species levels. Considering the order of median effective concentration values (EC50) and the levels of oxidative stress induced by the three tested QACs, their phytotoxicities in wheat seedlings increased in the following order: DDAC < DTAC < DBAC, which mainly depended on their characteristics and applied concentrations. These results, which illustrated the complexity of QAC toxicity to plants, could potentially be used to assess the risk posed by these compounds in the environment.

Assessment of the bacterial viability of chlorine- and quaternary ammonium compounds-treated Lactobacillus cells via a multi-method approach.

The assessment of the bacterial viability of chlorine- and quaternary ammonium compounds (QACs)-treated Lactobacillus cells by culture-dependent and -independent methods. Lactobacillus isolates (Lactobacillus plantarum G1, Lactobacillus plantarum B1, Lactobacillus brevis S1 and Lactobacillus paracasei W1) in biofilm and planktonic cell suspensions were treated with chlorine-based (0·018 and 0·18%) and QACs-based (0·2 and 2·0%) disinfectants for 5min and then analysed by plate counting, flow cytometry (FCM) and fluorescence activated cell sorting (FACS). The reaction of sessile cells to disinfectants was assessed with the confocal laser scanning microscopy (CLSM). Platecounts revealed L. paracasei W1 to be substantially inactivated by both disinfectants, while counts of the other isolates to be significantly reduced only by QACs, with L. plantarum B1 and L. brevis S1 showing a greater difference between QACs concentrations and cell types. In several cases, the disinfectants caused slightly higher inactivation of planktonic than biofilm cells, with L. plantarum B1 being significantly less sensitive to QACs in biofilm cells (P<0·05). Following FCM with a Syto® 9/PI assay, which addresses cell membrane integrity, the emergence of damaged (Syto® 9- PI+ ) and injured (Syto® 9+ PI+ ) subpopulations was often observed in cells when they were treated with QACs, whereas intact (Syto® 9+ PI- ) and unstained (Syto® 9- PI- ) subpopulations were mostly encountered in chlorine-treated cells. Except Syto® 9- PI+ , all subpopulations were recovered on agar plates following FACS, with biofilm cells showing higher culturability irrespective of conditions, probably because of the residues of the biofilm matrix which serve as a protective cover for the bacteria. The CLSM revealed a substantial cell membrane damage within the QACs-treated biofilms, however, some cells deep in the biofilm were still intact and thus remained protected against this disinfectant. We found that FCM/FACS proved useful in the analysis of lactobacilli membrane integrity in disinfection experiments as well as in recovery evaluation of planktonic-biofilm cell subpopulations. In turn, CLSM was particularly useful in investigating the resistance mechanism when Lactobacillus cells were embedded in biofilms. This study highlights the need for treatment optimization on a case-by-case basis to avoid the emergence of cells in intermediate states with recovery potential and to reach and, thus, kill all bacteria in already developed lactobacilli biofilms.

Accumulation of quaternary ammonium compounds as emerging contaminants in sediments collected from the Pearl River Estuary, China and Tokyo Bay, Japan

In this work, the distribution of quaternary ammonium compounds (QACs) in two dated sediment cores, collected from the Pearl River Estuary (PRE) and Tokyo Bay (TB), were investigated to understand the historical input of QACs and their diagenetic behavior in urban estuarine environments. The vertical variation profiles of QAC concentrations showed that benzylalkyldimethyl ammonium compounds (BACs) and dialkyldimethyl ammonium compounds (DADMACs) were widely used during 1970s and 1980s both in China and Japan. The declining environmental concentrations of QACs suggested a compositional change of commodities and the effectiveness of emission control strategies. For the individual QAC homologues, BAC homologues decreased significantly over time, while DADMAC compositions remained relatively stable. The differences in concentration and composition profiles of BACs and DADMACs in the sediment cores provided useful information on the patterns of use of QACs in China and Japan, as well as their diagenetic behaviors in the sediments.

Boron fixation effect of quaternary ammonium compounds (QACs) on sodium fluoroborate (NaBF4)-treated wood

AbstractAiming at a better leaching resistance of borate-treated wood, the quaternary ammonium compounds (QACs), didecyl dimethyl ammonium chloride (DDAC) and benzalkonium chloride (BAC) were reacted with sodium tetrafluoroborate (NaBF4). The anti-fungal properties of the resulting didecyl dimethyl ammonium tetrafluoroborate (DBF) and benzalkonium tetrafluoroborate (BBF) were tested by the Petri dish method. Poplar (Populus tomentosaCarr.) and Southern pine (Pinusspp.) blocks were treated through a two-step method at three molar ratios of NaBF4to the QACs. The retentions of the reactive components were determined by inductively coupled plasma atomic emission (ICP-AE) spectroscopy and the distribution of boron in wood was observed by scanning electron microscopy/energy-dispersive X-ray analyses (SEM-EDXA). Fourteen-day leaching and water absorption tests were also performed. DBF and BBF both exhibited moderate fungicidal activity againstTrametes versicolorandGloeophyllum trabeumin Petri dishes. The boron remaining in samples after leaching increased with increasing QACs concentration in the second step impregnation. SEM-EDXA showed no obvious morphological changes in the wood surface and DBF and BBF were only found in the cell walls. The water absorption of the treated samples were lower than the controls.

QuEChERS-based purification method coupled to ultrahigh performance liquid chromatography–tandem mass spectrometry (UPLC–MS/MS) to determine six quaternary ammonium compounds (QACs) in dairy products

QuEChERS-based purification coupled with UPLC–MS/MS method, was developed for six quaternary ammonium compounds (QACs) determination in dairy products. Powder samples were firstly dispersed by water. Protein in liquid milk was precipitated and sample solution was extracted by acetonitrile. QuEChERS-based purification was used to purify the solution. QACs were finally separated by HILIC column and detected in MRM mode of MS/MS under ESI+. The stable isotope benzyl-2,3,4,5,6-d5-dimethyltetradecylammonium bromide (C14-BAC-d5) was used as an internal standard. This method was validated in terms of linearity, sensitivity, precision, accuracy. Linear relations were favorable for QACs over the selected concentration ranges of 0.2–50μg/L, with correlation coefficients greater than 0.999. The limits of detection (LODs) were in the range of 0.4–14.5μg/kg. Recoveries were between 91.2% and 115% with RSDs of 2.8–7.5% for intra-day precision and 3.7–6.7% for inter-day precision. This validated method was successfully applied to determine the QACs concentrations in dairy products.

Potential Impact of the Resistance to Quaternary Ammonium Disinfectants on the Persistence of Listeria monocytogenes in Food Processing Environments.

The persistence of certain strains of Listeria monocytogenes, even after the food processing environment has been cleaned and disinfected, suggests that this may be related to phenomena that reduce the concentration of the disinfectants to subinhibitory levels. This includes (i) the existence of environmental niches or reservoirs that are difficult for disinfectants to reach, (ii) microorganisms that form biofilms and create microenvironments in which adequate concentrations of disinfectants cannot be attained, and (iii) the acquisition of resistance mechanisms in L. monocytogenes, including those that lead to a reduction in the intracellular concentration of the disinfectants. The only available data with regard to the resistance of L. monocytogenes to disinfectants applied in food production environments refer to genotypic resistance to quaternary ammonium compounds (QACs). Although there are several well-characterized efflux pumps that confer resistance to QACs, it is a low-level resistance that does not generate resistance to QACs at the concentrations applied in the food industry. However, dilution in the environment and biodegradation result in QAC concentration gradients. As a result, the microorganisms are frequently exposed to subinhibitory concentrations of QACs. Therefore, the low-level resistance to QACs in L. monocytogenes may contribute to its environmental adaptation and persistence. In fact, in certain cases, the relationship between low-level resistance and the environmental persistence of L. monocytogenes in different food production chains has been previously established. The resistant strains would have survival advantages in these environments over sensitive strains, such as the ability to form biofilms in the presence of increased biocide concentrations.

Immobilization of Pseudomonas putida A (ATCC 12633) cells: A promising tool for effective degradation of quaternary ammonium compounds in industrial effluents

Pseudomonas putida A (ATCC 12633) were encapsulated in Ca-alginate and their ability to degrade the quaternary ammonium compounds (QACs) tetradecylbenzyldimethylammonium chloride (C14BDMA), hexadecylbenzyldimethylammonium chloride (C16BDMA) and benzalkonium chloride (BAC) (a mixture 1:1 of C14BDMA and C16BDMA), was tested and compared with the degradation of the same compounds by freely suspended cells. Degradation was carried out in pH 7.4 buffered medium, at 30 °C with agitation at 100 rpm. After 24 h of incubation immobilized cells degraded 90% of 35–315 mg l−1 of C14BDMA, C16BDMA and BAC, whereas free cells were unable to degrade concentrations above 35 mg l−1. Immobilized cells of P. putida removed 80% QACs of an industrial effluent in 48 h under both sterile and non-sterile conditions. Degradation of QACs carried out using the non-sterilized effluent showed that the beads could be reused up to four cycles without changing the degradation efficiency. The reduction in the QACs concentration after treatment with immobilized cells can be correlated with the reduction in the phytotoxicity to Lactuta sativa seed germination and root elongation. We conclude that immobilized QACs-degrading bacteria represent a promising tool for bioremediation of QACs in industrial wastewater systems.

Field leaching of alkaline copper quaternary-treated red pine lumber over 3 years: long-term dynamics

Alkaline copper quaternary (ACQ), a wood preservative, consists of copper oxide and quaternary ammonium compounds. Three red pine piles were monitored over 3 years to evaluate the dynamics of contaminant leaching from ACQ-treated and untreated lumber. There were small temporal changes in the volumetric leachate/rain ratio with the ACQ-treated lumber, while the volumetric ratio decreased across the 3 years with the untreated lumber, most likely due to considerable weathering that increased the capacity of the untreated lumber to absorb rain water. The average copper (Cu) concentration in leachate from the ACQ-treated lumber (4,033 μg/L) was much higher than that in leachate from the untreated lumber (87 μg/L) and rain (48 μg/L) in the first leaching year. Cu concentration in leachate from the ACQ-treated lumber in the second and third years decreased to 46-51% of that in the first year. There were significant seasonal decreases of Cu concentration in leachate from the ACQ-treated lumber, which were correlated to exposure time and meteorological parameters. ACQ-treatment did not affect leachate pH and concentrations of quaternary ammonium compounds and chemical oxygen demand. There were insignificant temporal changes of leachate pH and concentrations of chemical oxygen demand and total dissolved solids in leachate from both ACQ-treated and untreated lumber piles.

Decreased activity of commercially available disinfectants containing quaternary ammonium compounds when exposed to cotton towels

Health care-associated infections (HAIs) are a significant problem in hospitals, and environmental surfaces have been implicated as a source of HAIs in the hospital environment. Furthermore, Gram-negative and Gram-positive bacteria can persist on dry environmental surfaces for as long as several months. Poorly cleaned surfaces may serve as vehicles for microbes, which may then be transferred to patients. Cotton and microfiber towels were both tested for their abilities to bind quaternary ammonium compounds (QACs). The towels were exposed to 3 commercially available disinfectants for 0.5, 30, and 180 minutes. Germicidal spray tests (GSTs) were performed for all towel eluates in accordance with the AOAC International method 961.02. Cotton towel eluates were analyzed for QAC concentration using high-performance liquid chromatography. QAC concentrations were reduced by up to 85.3% after exposure to cotton towels, resulting in failure of the disinfectants exposed to cotton towels in 96% of the GSTs. The use of cotton towels with QAC-based cleansers should be reconsidered, particularly in hospitals where effective cleaning of the patient environment is needed to reduce the risk of HAIs.