Stan Atkins, group chief executive officer of British Institute of Cleaning Science reports
As being clean is a perception, sometimes when we visually check a surface for dirt and dust and it is bright and shiny we immediately perceive it is clean – this is not always enough. This surface, although clean to the eye, could have many micro-organisms or other invisible contamination that makes it unsuitable for its purpose. In this column I will be discussing the three most commonly used methods of measuring or identifying the presence of contamination.
This is the most precise form of checking for microbiological contamination. It consists of taking a number of swabs prior to cleaning and directly after cleaning and will show a bacterium count and even identify strains of bacteria present. Microbiological measurements are useful for testing areas and rooms where microbiological hygiene is of importance, such as in hospitals and other healthcare establishments. The main disadvantage with this method is the time it takes to get the results back. Often incubation is used which requires at least 24 hours. Identification then makes the process even longer.
ATP stands for Adenosi-Tri-Phosphate. In living cells energy is stored in this substance and when it reacts to an enzyme compound, luciferin/luciferase, light is created. This light can be measured using a photo meter and the results expressed in RLUs – relative light units. Therefore the more ATP there is the more light there is. Although there are various manufacturers, the test usually takes the form of a moist cotton bud swabbing a surface which is then placed in a solution with reagents. Once shaken to loosen the ATP it then reacts with the enzyme and is placed in a photo meter for the measurement of RLU. Although the ATP measurement is quick and simple to execute, its results are sensitive to an exact method of swabbing. It is therefore sensible to repeat measurements a few times and compare averages. Other things to take into consideration when using this method are that different manufacturers equipment can give different readings and the process doesn’t recognise viable fungi spores as they do not contain ATP. This method is mainly used by the food, catering and the process industries.
Ultraviolet light can be used to identify the location of mould, bacteria, urine, and many other contaminants. It instantly shows residue and is particularly good at identifying protein. Materials, namely flavins, fluoresce or glow when hit with ultraviolet light. Other materials, like dipicolinic acid, fluoresce with ultraviolet light when another element, such as terbium reacts with it. Bacteria and germs gather in areas with large amounts of flavins, like washroom fixtures covered with uric acids and soap scum. By disclosing areas with high concentrations of flavins, ultraviolet light can also indicate areas at high risk of breeding germs. Additionally, bacterial endospores contain dipicolinic acid, making it possible to specifically confirm the existence of germs in a suspected area. Some ultraviolet light technologies claim not only to identify germs, but to sterilise and sanitise contaminated areas. The disadvantages of ultraviolet Light include its inability to confirm the type of contamination and it is most effective when used in subdued lighting.