Infection prevention
Disinfectant type
QAC
Spectrum of activity (vegetative cells)
Broad
Tuberculocidal activity
Effective
Sporicidal properties
Good Stability Corrosive Odour
Relative toxicity
Good Non- corrosive Average Low
Suitability of large surface areas
Yes Residues
Effectiveness in the presence of soil
Low Good,
enhanced by surfactant properties
Biguanide
Average (less active Weak against Gram-
negative bacteria) Amphoteric Broad Weak None Good Non- corrosive Aldehyde Broad Weak None
Unstable, Non- short
reactive time
Phenolics
Good bactericidal, weak fungal activity
Good Weak Good Non- Above
corrosive average odour
Table 1: Comparison of key factors between different disinfectant types
through multiple mechanisms. These mechanisms include adsorption onto, and diffusion through the cell wall; binding to, and disruption/ disorganisation of the cytoplasmic membrane; the release of low molecular weight cytoplasm constituents; the degradation of cell contents (such as proteins and nucleic acids); and triggering cell wall lysis by autolytic enzymes, leading to cell death. Of these different mechanisms, the most effective kill mechanism is membrane binding, leading to the disruption of the microbial cell membrane’s physical and ionic stability. This serves to cause cellular components
to leak and renders to cell non-viable (as detected by the release of potassium from cell membranes).15
The chemical design of QACs
is essential to their antimicrobial properties, which is attributed to the ionic binding capabilities and hydrophobic interactions of the QAC with microbial membrane surfaces. This occurs since the QAC is positively charged and, as it comes into contact with a microbe, its cationic head becomes oriented outwards, and the hydrophobic tail is then attracted to the lipid bilayers of a bacterium. This attractive process leads to monolayer or supramonolayer deposition of the QAC on the cell surface and this causes the subsequent rearrangement of the membranes and eventual leakage of the organism’s intracellular constituents.16
Biofilm formation by microorganisms is a widespread problem in hospital and pharmaceutical environments. Biofilm community development by microorganisms begins with the cell adhesion to surfaces, a process dependent upon the interplay of physicochemical forces. Many biofilms develop resistance to disinfectants by quenching the active ingredient through slime-like protective layers. Research suggests that QACs can coat plastics and hence prevent microbial adhesion to surfaces (imparting an antiadhesive effect).17 QACs are also effective in destroying biofilms.18 This includes biofilms derived from specific pathogen of concern, including multidrug- resistant Pseudomonas aeruginosa and methicillin-resistant Staphylococcus aureus (MRSA).19
QACs are also effective against the
other microorganisms of concern that form the collective of ESKAPE pathogens (Enterococcus faecium, Klebsiella pneumoniae, Acinetobacter baumannii, and Enterobacter spp.). QACs are also effective against other nosocomial infectious agents like plus Shigella spp., and the dimorphic yeast Candida albicans and the filamentous fungus Mucor (and other Mucoraceae).20 Another reason why continuing innovations
in QAC technology is important is to safeguard against microbial resistance (although
‘resistance’ is best understood as ‘tolerance’). While increases in tolerance to QACs have been observed (such as a need to increase the minimum inhibitory concentration to achieve the same biocidal effect), there is no straightforward evidence to support the development of resistance to QACs. However, the issue of tolerance adds weight to the necessity to ensure the later generational QAC products are used.
Comparison with other disinfectants The disinfectants that are sometimes used in place of QACs are: l Aldehydes. l Alcohols. l Hydrogen peroxide based formulations. l Biguanides (and bisbiguanides). l Amphoterics.
Aldehydes, biguandies, amphoterics, and QACs each kill microorganisms in similar ways, especially through cell membrane targeting. However, there are distinct factors that need to be evaluated when selecting between different disinfectants. These are considered in Table 1 (to which some other commonly used disinfectants have been added for comparison purposes). The data within the table was obtained from a literature review.
June 2025 I
www.clinicalservicesjournal.com 43 Pungent corrosive High toxicity (irritant) High
Variable (weak on rubber
and plastics) Yes Yes Average Low Yes Yes (visible) Yes (sticky) None Good Non- corrosive Average Low Yes Yes (visible)
Inactivated by highlevels
(also inactive at high pH)
Inactivated by
high levels of soil, but overall good
Weak in the presence of soil
Average (and inactivated
in hard water)
t
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