INF ECTION P R EVENTION
charges from negative to positive.25
With
viruses, the virucidal mechanism of QACs for lipophilic enveloped viruses appears to involve disruption or detachment of the viral envelope with subsequent release of the nucleocapsid.26
QACs interfere with the viral fusion process and effectively inhibit virus replication in cells.27
Over time, the chemical formulation of QACs has evolved and with this the spectrum of activity has broadened and the possibility of microbial resistance has receded. The first generation disinfectants used only alkyl dimethyl benzyl ammonium chloride as the quaternary ammonium salt. Through subsequent generations, the fourth generation QACs came to include bis-octyl, bis-decyl, octyl-decyl and other combinations, increasing the bactericidal effect and creating a chemical formulation that was more resistant to hard water and organic interferences. Fifth and sixth generation QACs showed
further enhancements with microbial kill through synergies of chemicals from early generations, which created an even wider kill spectrum.28
With non-enveloped viruses,
same level of efficacies on different groups of microorganisms, for different levels of organic matter, on different types of surfaces. Compared with more traditional formulations of disinfectants (such as phenolics, amphoterics, chlorine compounds and peroxides), QACs are often less damaging to surfaces, are safer to use, and meet environmental regulations for disposal (via biodegradation and sorption to wastewater biosolids as part of wastewater treatment).30
Today, some commercially
available QACs are seventh generation products (combining the steps involved in formulating fifth and sixth generation products), such as the Biochem formulation (Bioguard). These recent formulations possess multiple modes of action, combining QACs with actives found in other disinfectants to provide a greater log reduction within relatively short application times compared with previous iterations of QAC generations.29
As well as being effective disinfectants, QACs function as cationic detergents and they are suitable for removing organic material, such as protein residues, enabling the disinfecting action to take place unimpeded by soiling. Newer generations of QACs produce less foam, are not affected by protein residues, and they are also tolerant of anionic residues.
Not all disinfectant groups manifest
Spectrum of activity The antimicrobial properties of quaternary ammonium compounds were discovered in the early part of the twentieth century.31 QACs are lethal to a wide variety of organisms, including vegetative cells of Gram-positive and Gram-negative bacteria, fungi, parasites (e.g., Leishmania major, Plasmodia falciparum), and lipophilic (enveloped) viruses (and some hydrophilic (non-enveloped) viruses like Adenovirus). In assessments against the main nosocomial pathogens of concern, QACs have been shown to be effective in numerous studies, including efficacy against the so-called and globally serious ESKAPE pathogens (Enterococcus faecium, Staphylococcus aureus (including the methicillin-resistant form), Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.), plus Shigella spp., and the yeast and Candida albicans.32, 33 Generally, QACs kill Gram-positive bacteria faster than Gram-negative bacteria, due to factors based on the outermost layers of bacterial cells which impart a significant effect on the cells’ susceptibility (or insusceptibility) to the disinfectant. Optimising the contact time is important for killing both bacterial types. While older generations of QACs do not display efficacy against microbial spores, the incorporation of other chemicals has created synergies that have enabled fifth, sixth and seventh generation QACs to show measurable action against bacterial and fungal spores.34 Efficacy is measured through the
evaluation of the disinfectant concentration and contact time, using preparations of microorganisms, tested against a reputable standard, such as the European norms (the CEN standards) for suspension and surface testing. Further efficacy data can be shown through the determination of the minimum inhibitory concentration (MIC), via liquid dilution methods using a 48-well microplate, which is used to derive the lowest concentration of an antimicrobial that will inhibit the visible growth of a microorganism. Since there are different formulations of QACs, data relating to a specific manufacturer should be requested and evaluated. An additional pathogenic organism of concern is the causative agent of tuberculosis: Mycobacterium tuberculosis. The risk posed has been complicated by a global increase in multi-drug resistant types of the bacterium. Tuberculosis infection occurs through inhalation of the bacterium, which then travels to the alveoli of the lungs.35 Patients who have pulmonary or laryngeal tuberculosis pose a risk of infection, especially if they are coughing due to the generation of aerosols; furthermore, medical equipment coming into contact with the mouth is potentially contaminated and this contamination can be transferred where items come into contact with work surfaces. QAC disinfectants have efficacy against M. tuberculosis, as indicated in CDC guidelines36 and EDC recommendations.37
Microbial resistance is a matter of public
concern. There is no clear evidence to support the development of resistance to QACs38, 39
, although some bacteria have
been found to possess a QAC gene that may provide resistance when QACs are applied at levels below the target minimum inhibitory concentration value.40
Later generations
of QACs overcome this potential concern through a wider synergy of antimicrobial compounds.
Therefore, against the range of
microorganisms found within the healthcare environment and their physiological states, QACs display a very broad spectrum of activity and a comparable, and often greater, efficacy compared with other disinfectant types (phenols, biguanides, amphoterics, and chlorine products) formulated at levels that are safe for personnel to use and which pose a low environmental hazard.41
Application of QACs on the ward QAC disinfectants have the advantage of being compatible with the common surface materials found in the clinical setting, including throughout the ward. Compatibility includes inanimate objects like various forms of plastics, stainless steel, bedding, and uniforms worn by healthcare staff. Therefore, as well as demonstrating effective kill against hospital pathogens, QACs can be applied to
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