Colorimetric detection of residual quaternary ammonium compounds on dry surfaces and prediction of antimicrobial activity using bromophenol blue

Abstract

Controlling and monitoring the residual activity of quaternary ammonium compounds (QACs) are critical for maintaining safe yet effective levels of these agents in the environment. This study investigates the utility of bromophenol blue (BPB) as a safe, rapid and user‐friendly indicator to detect in situ residual QACs dried on hard, non‐porous surfaces, as well a means to assess their antimicrobial efficacy. At pH 7, BPB has a purple colour which turns blue upon its complexation with QACs such as didecyldimethylammonium chloride (DDAC). BPB itself has no antimicrobial properties up to 400 ppm. Within the range of 0–400 ppm, BPB colour change was tied to specific DDAC antimicrobial performances with a detection threshold of 100 ppm. BPB concentration and application volume could be adjusted such that a colour shift from purple to blue correlated with a set percent reduction (>99·9%) in test bacteria (Staphylococcus aureus and Klebsiella aerogenes). The BPB solutions developed in this study yielded similar colour shifts on polycarbonate and stainless steel surfaces and did not cross‐react with chemical ingredients commonly found in sanitizers and disinfectant products. Overall, this study suggests that BPB provides a simple solution to safely monitor the post‐application level and biocidal activity of residual dried QACs on surfaces.

A rich gallery of carbon dots based photoluminescent suspensions and powders derived by citric acid/urea

“…Cytotoxicity studies were assessed with the use of the standard MTT (3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide) assay (Sigma Aldrich) and the epithetical HeLa cervix cancer cell line. This immortalised cell line is very well characterised with its full genome being sequenced 78 and is considered as a model line by regulatory odies such as the OECD, being widely used for the assessment of nanoparticles toxicity 79 , 80 . The HeLa cells were cultured in Dulbecco's Modified Eagle Medium (DMEM, ThermoFisher Scientific) supplemented with 10% Fetal Bovine Serum (FBS, ThermoFisher Scientific) and 1% Penicilin-Streptomycin (10,000 U/mL, ThermoFisher Scientific).…”

Physical mechanisms driving the reversible aggregation of Staphylococcus aureus and response to antimicrobials

“…The consequence of S. aureus cell aggregation was studied in relation to bacterial tolerance to QACs, which are broad-spectrum antimicrobials 20,21 commonly used in disinfectant and sanitizer formulations. QACs are membrane-active agents comprising a positively-charged head which electrostatically interacts with the negatively charged bacteria membrane, and a hydrophobic tail which can penetrate into the membrane ultimately leading to membrane structural damages and bacteria lysis 20 .…”

“…The untreated controls showed no reduction in the cell population (see Table S3 in Supplements for CFUs), suggesting that pH alone did not significantly impact cell viability. TAT broth was previously shown to be an effective media to neutralize DDAC 21 .…”

Evaluation of Quatsome Morphology, Composition, and Stability for Pseudomonas aeruginosa Biofilm Eradication

“…Therefore, QS preparations are not homogeneous, yet it is important to know the QAC concentration in the QS suspension before the antimicrobial ability can be quantified. Absorbance-based colorimetric methods have been used previously for phospholipid or QAC-containing nanovescicles. ,− Ammonium ferrithiocyanate and bromophenol blue are the most commonly used dyes as they form complexes with the quaternary ammonium head groups. − These methods determine only the QAC concentration, and the quantification of sterol content in the nanovesicles is often not determined, making it difficult to pinpoint the molecular causes of any observed differences in the activities of vesicle preparations and their starting materials. The molar ratio ( Q value) of the cholesterol versus QAC in QS systems has always been of interest of study.…”