INF ECT ION PR EVENT ION & CONT ROL
Disinfectants and the ‘entourage effect’
In the wake of COVID-19, the role of surface and skin disinfectants is under close scrutiny. Dr. Andrew Kemp considers the resistance challenge and discusses the efficacy of 5th generation SiQuat compounds, compared to other chemistries.
The activity of disinfectants against microorganisms depends on a number of factors, some of which are intrinsic qualities of the organism, others of which are the chemical and external physical environment. The “Entourage effect” described by Ethan B Russo in January 20191
is based
on the idea of the holism theory, which is credited to Aristotle, who said “the whole is greater than the sum of the parts”.
Background Quaternary ammonium compounds have been around since the early 20th century and are used in many cleaning products. There are essentially two main groups of disinfectants that use quaternary ammonium type compounds, those that have a silane attached (SiQuats) and those that do not (Quats). While their mode of action (MOA) is essentially the same, the spectrum of species kill, and the level of persistence (length of time they remain in place to continue killing) are very different for each variation. SiQuats will bond to surfaces and skin and become, in some cases, almost impossible to remove without wearing away or damaging the surface to which they are bonded. The resultant effect, therefore, is an antimicrobial compound that remains in place killing microbes for days months or even years.2,3,4
Properties of Quats and SiQuats Individual SiQuats have different spectrum of kill, which can change based on concentration, ambient temperature
intended surface, or break apart leaving an unstable, unpredictable compound.5 Since 1952, when SiQuats were first introduced, many chemical manufacturers have tried and failed to produce these multiple SiQuat compounds that are now known as 5th generation SiQuats. The goal being to produce a persistent, rapid acting compound with a full spectrum of microbial kill. There are two main reasons why this goal has been so keenly sought after: l Increased efficacy. l Decreased potential for microbial resistance to build up against the compound.
Bacteria can become resistant to disinfectants.
and humidity. This is not unusual for disinfectants, as some actually change their mode of action based on the concentration used. The Achilles heel for Quats is that, although they are easily combined to give a full spectrum of kill, they are also easily removed from surfaces. Therefore, after each subsequent clean, they need to be re
applied.For SiQuats, although they will stay around after cleaning (or hand washing) the biggest problem is the difficulty in mixing them together to form multiple SiQuat compounds that have a full spectrum of kill. They either stick to each other and not the
Without proper guidance on both type and frequency of surface and skin testing, it is difficult to see how healthcare systems around the world will reduce infection rates.
20 l
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Organisations, such as NASA, have combined Quat compounds in an effort to kill bacteria on the International Space Station (ISS), only to find that they produce bacteria that are resistant to Quats and now multiple Quats.6
One of the mechanisms
that bacteria can use to become resistant to disinfectants is known as the Efflux pump.7 If a bacterium comes into contact with a disinfectant at subtherapeutic levels, it has the potential to gain resistance to that disinfectant in the same way as it may do if it came into contact with an antibiotic at subtherapeutic levels. In fact, in some cases, by becoming resistant to either one, it has been proved that it can then become resistant to both.8
had NASA used a 5th generation SiQuat compound, instead of a simple multiple Quat combination, that resistance could have been avoided, as SiQuats do not reduce in therapeutic efficacy over time.
SiQuat generational differences Simple Quats first appeared in around 1915 and were used in many areas of industry and in the military as surfactants and disinfectants. It is difficult to trace exactly, but it is likely that resistance to these was first seen early in the 2nd world war, when combinations were tried to reduce resistance
OCTOBER 2020
It is possible that
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