Why You Really Need to Know Your Disinfectants
At a time when we're being bombarded with advertising, guidance, and often conflicting information on containing the spread of Covid-19, taking the time to consider what public health advice to clean, clean properly, and clean often actually means, can yield dividends.
For the success of any disinfection operation is determined as much by science as by the skills, and experience of cleaning operatives which requires an awareness of the different terms used by chemical manufacturers - and even greater awareness of a market tendency for these terms to be applied broadly with little regard to their true meaning.
Bactericides are substances that kill bacteria - microscopic, single-cell organisms with a simple internal structure containing 'free-floating' DNA (i.e., no nucleus; ‘prokaryotic’). Most bacterial cells are surrounded by an outer cell wall and an inner cell membrane, whilst some have no cell wall, and some have a third protective outer layer called a capsule.
A gram stain is used to identify and classify bacteria based on their cell wall composition; a gram stain is a test that is able to stain ‘Gram-positive bacteria’, as they do not have an outer cell wall, whilst ‘Gram-negative bacteria’ do not pick up the stain, due to the presence of an outer cell wall. Further classification of bacteria is based on their shape; round bacteria are called ‘cocci’ (singular ‘coccus’), cylindrical, capsule shaped bacteria are called ‘bacilli’ (singular ‘bacillus’), and spiral bacteria are called ‘spirilla’ (singular: ‘spirillum’).
Bactericides kill bacteria in a variety of ways, including protein denaturation (breakdown), penetration of the cell wall, loss of intracellular (within the cell) contents, inhibition of protein synthesis (building of proteins), decreased oxygen uptake, DNA fragmentation, depression of DNA synthesis, depression of cell wall synthesis, decreased bacterial cell ‘energy’ production, or the production of destructive ‘free radicals’ - highly reactive atoms that can attack and damage membrane lipids, DNA or other essential cell components. Bacterial spores (highly resistant, dormant structures formed to ensure the survival of bacteria through adverse environmental conditions) cannot be destroyed by all chemical disinfectants and must be killed by sterilization (typically at high temperatures and under high pressures).
Virucides are substances that kill viruses. Viruses consist of three main ‘building blocks’: (1) Ribonucleic acid (RNA), the viral genetic material similar to DNA; (2) proteins; and (3) lipids, the outer coating of the virus that protects the genetic material and aids with viral spread and cellular invasion. These three components spontaneously self-assemble to form a complete virus, with weak ‘non-covalent’ bonds between the proteins, RNA and lipids.
Virucides can kill viruses in multiple ways, including protein denaturation, loss of intracellular contents,
inhibition of protein synthesis, decreased oxygen uptake, DNA fragmentation, alteration of RNA synthesis,
the production of destructive free radicals and by altering the integrity of the viral outer lipid membrane.
Virucides in particular are effective at blocking RNA synthesis, as this is needed for viral multiplication.
Fungicides are substances that kill fungi. Fungi are complex, ‘eukaryotic’ (i.e., DNA is contained within a membrane structure called a nucleus) cells, similar to animal cells, possessing an inner cell membrane and an outer cell wall. Fungi cell membranes contain a specific type of cholesterol, called ‘ergosterol’, which helps to maintain cell membrane fluidity and integrity.
Fungicides can kill fungi in multiple ways, including protein denaturation, decreased oxygen uptake, depressed DNA synthesis, inhibition or reduction of protein synthesis, DNA fragmentation, alteration of RNA synthesis, and the production of destructive free radicals. Other fungicides act to inhibit the synthesis of, or directly interact with, ergosterol in the fungi cell membrane.
Notwithstanding all of the above, it's still worth remembering throughout the coronavirus pandemic that there's a simple message to follow.
Wash your hands regularly with soap and water all the way up to your wrists and for a minimum 20 seconds, wash down all surfaces and equipment regularly with an effective detergent or soap, and focus disinfection actions on high-touch critical areas by implementing a regular programme of targeted hygiene within your facility.