Does your cleaning chemical kill the COVID-19 virus?
By Annette Sansom - June 2020
Companies want to be sure that their cleaning inactivates the virus that causes COVID-19. As you might imagine, testing
whether a particular cleaning chemical or sanitiser inactivates the virus is a challenge. Not least, working with a human pathogen like this is
fraught with problems. One way around this is to use a ‘surrogate’ that is structurally similar to the SARS-CoV-2* but which is much safer to use
(*severe acute respiratory syndrome coronavirus 2, that causes COVID-19).
New test for virus ‘kill’
We have developed and validated a test in our microbiology laboratories taking this exact approach. It can test the
effectiveness of sanitisers in solution and on surfaces. This means it can be used by companies who want to compare the efficacy of different
sanitisers or assess the effectiveness of a surface cleaning regime. And because the surrogate is safe, it can be used to test control measures in
the real environment (for example, on a factory or retail surface) and even on hands.
The really interesting feature is that the test doesn’t look for the surrogate directly – it looks for activity of the
surrogate. So, it won’t detect inactivated virus even if it is there – it will only detect active virus. Intrigued? Then read on.
The surrogate story
Strictly speaking viruses aren’t ‘alive’ – not in the way that bacteria, plants and animals are alive. They are physical
structures that hijack living things to make many copies of themselves – even though in doing so, many (like SARS-CoV-2) cause death and destruction
for the cells they infect.
But them being just ‘physical particles’ provides an advantage. Other viruses with a very similar structure will ‘behave’
in a similar way in many circumstances. And these provide the surrogate approach.
The virus Phi6 is the one we are using as a surrogate for SARS-CoV-2. (Incidentally Phi rhymes with pie not pea, and you
might also see it written as the Greek letter Ф). Structurally the Phi6 (or Ф6) virus particle is very similar to SARS-CoV-2: they are about
100nm, they have a lipid (fatty) envelope, and their genes are made of RNA. Recent publications have suggested that Phi6 is an appropriate surrogate
for infectious enveloped viruses like coronavirus and influenza virus.
Phi6 is a virus that infects the bacterium Pseudomonas syringae. A virus that infects bacteria is called a
bacteriophage (or phage for short). It does not infect plants or animals, including humans - and so is much safer to work with than SARS-CoV-2.
Plaques on your lawn
So, how does it work? The key is looking at the damage caused by any active Phi6 in a ‘lawn’ of Pseudomonas syringae.
You can grow a ‘lawn’ of bacteria by pouring a small amount of liquid bacterial culture over the surface of a gel in a petri dish and allowing the
bacteria to grow. But if you add phage to the liquid culture, the lawn will have holes (plaques), where the phage has killed some of the bacteria.
The more plaques you get, the more phage is in your sample. The photograph shows what phage damage in a bacterial lawn looks like. The circles are
the plaques where the bacteria have been killed.
If a cleaning chemical has inactivated the phage there will be fewer or no plaques in the lawn – so you can compare different
cleaning chemicals based on how much they can prevent plaques compared to control samples.
The circular ‘plaques’ are areas where bacteria in the pale lawn have been killed by phage
Get in touch
We have used the test to check the efficacy of sanitisers and are keen to help you get your approach to sanitising and
cleaning right for you and your environment. This builds on our long-established work assessing the efficacy of cleaning chemicals for killing
bacteria (bactericides) in suspension (following BS EN 1276) and on surfaces (following BS EN 13697).
If you would like us to test cleaning chemicals, cleaning methods or surfaces for you, or just find out more about how our
virologists could help you, please get in touch. We’d love to talk.
About Annette Sansom
Annette Sansom joined Campden BRI in 1998 as a senior technician in the Microbiological Analytical Services group having
graduated from the University of Bedfordshire with a BSc in Biology. Read more...