Infection prevention


combined chemistries for greater efficacy. Since commercialisation during the 1940s, the


QACs have been used as active ingredients in an array of different disinfectant and sanitiser products. QACs, in milder and less concentrated forms, are also added to some cleaning agents and to many personal care products, including mouthwashes, detergents and shampoos. Chemically, the QACs used in disinfectants have shorter alkyl chain lengths (C8–C16) compared with those used in personal care products (alkyl chains as long as 22 carbons).10 The C16 chain length is effective against


Gram-negative bacteria because of the ability to bind with the lipid components in the bacterial cell wall. Irrespective of the chain lengths, QACs possess properties that act against a broad range of microorganisms (including sporostatic properties) and inherent surfactant properties also provide a degree of cleaning efficiency. What is of focus in this article are they types of QACs developed and assessed for use as disinfectants suitable for the healthcare facility. In these cases, QACs deployed as disinfectants, typically have a concentration falling between 400 and 500 ppm. To maintain efficacy, it is important that the optimal concentrations, as indicated on product labels, are used, and monitored. In terms of the broad range of microcidal


activity, QACs are effective against most vegetative bacteria, enveloped viruses, and many types of fungi.11


First generation


l Benzalkonium compounds, such as alkyldimethylbenzyl ammonium chloride, also known as “benzalkonium chloride”.


l Substituted benzalkonium compounds, such as nalquil ethyl benzyl dimethyl ammonium chloride. Second generation


Third generation


l ‘Dual quats’ formed from blends of 1st and 2nd generation QACs of specific chain length distributions.


l ‘Twin chain’ products and examples like didecyldimethyl ammonium chloride. Fourth generation


Fifth generation


l Mixtures of selected twin chain QACs with established single-chain compounds provided the basis for fifth generation products.


Sixth generation


l Mixtures of selected twin chain QACs with established single-chain compounds provided the basis for fifth generation products.


l Combining Bis-QACs and polymeric QACs. Seventh generation


Figure 1: Representation of the generational development of QACs 42 www.clinicalservicesjournal.com I June 2025 The efficacy is dependent


In terms of the broad range of microcidal activity, QACs are effective against most vegetative bacteria, enveloped viruses, and many types of fungi.


upon the chemical formulation of the QAC and its concentration (the proportion of the product containing a QAC as the active ingredient will range from <1% to 80%). Laboratory studies will establish the appropriate concentration against nosocomial pathogens and the time required to achieve sufficient microbial kill. All disinfectants work optimally when applied to a surface by wiping or mopping12


(however, the choice of


materials is important to avoid over absorbency of the active ingredient or inactivation of the disinfectant from wiper material).13


Generational development Among all the diverse types of biocides available, QACs for disinfection have undergone the most research and development. This is manifest in QACs moving through different generations, with each generation marking a new scientific breakthrough and strengthening the efficacy of the chemical agents (with many important insights gained from laboratory methods like gas chromatography and mass spectrometry) leading to improved and novel synthesis. The generational process is shown in Figure 1. Typically, third generation QACs upwards


are more efficacious and suitable; and later generation enhancements further the biocidal efficacy and surfactant properties. Hence, it is important to invest in the later


generations of QACs to meet the challenges presented by the modern healthcare facility. This is evident when later generational QACs are examined against biocidal concentrations considered to achieve membrane permeabilisation, where kill rates are faster and longer lasting. The reason why third generation QACs


onwards saw a significant improvement in biocide activity arises from the synergistic effects of combining different QAC chemicals. Examples include blending single chain QACs with polymeric QACs (such as polyhexanide), which creates more potent chemical synergies. The advantage of these combined chemical compared with earlier generations is because the resultant blend widens the spectrum of activity, and it also helps to prevent bacterial resistance to the continued use of a single molecule. Furthermore, such products have lower toxicity. Antimicrobial activity was enhanced further with fourth and fifth generation formulations since these products have proved to be more effective in the presence of residues from other sources that might remain present on a surface, including anionic surfactants, protein soiling and water. With more recent QACs, research focuses


on developing optimal structural features such as improving aqueous solubility, experimenting with different counterions, balancing chemical stability, and ensuring biodegradability.14 Counterions tend to be based on chlorine, bromide or methylsulfate anions, although alternatives include lactates, formates and acetates have also been explored. The blending of QACs with counterions creates synergistic effects that serve to increase the spectrum of activity against a range of bacteria, viruses, and fungi. The stability of QACs is relatively high compared to most other types of disinfectants, providing potential shelf-lives of several years, since QACs do not undergo the exothermic decomposition reactions seen with other disinfectant types.


Microbial kill mechanisms Most QACs have a wide spectrum of activity, and this is due to their ability to kill microorganisms


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28  |  Page 29  |  Page 30  |  Page 31  |  Page 32  |  Page 33  |  Page 34  |  Page 35  |  Page 36  |  Page 37  |  Page 38  |  Page 39  |  Page 40  |  Page 41  |  Page 42  |  Page 43  |  Page 44  |  Page 45  |  Page 46  |  Page 47  |  Page 48  |  Page 49  |  Page 50  |  Page 51  |  Page 52  |  Page 53  |  Page 54  |  Page 55  |  Page 56  |  Page 57  |  Page 58  |  Page 59  |  Page 60  |  Page 61  |  Page 62  |  Page 63  |  Page 64  |  Page 65  |  Page 66  |  Page 67  |  Page 68