Effect of UV-C on Escherichia coli, Staphylococcus aureus, Salmonella Typhimurium and SARS-CoV-2 Virus Surrogate (MS2 bacteriophage) Inoculated onto Stainless Steel Surface

Stainless steel is commonly used in the food, beverage and medical industry due to ease of cleaning and sanitising. It is an ideal material for food processing, catering and medical equipment or devices because of its inability to impact colour, odour and flavour to products and high corrosion resistance. However, stainless steel is susceptible to bacterial adhesion which can lead to cross contamination and spread of spoilage and or pathogenic microorganisms. Chemical disinfectants have been used in industries to address the problem associated with microbial adhesion on stainless steel. However, research has shown that bacterial cells attached to surfaces can withstand these disinfectants due to the development of extracellular polymers that act as a protective cover against these chemicals. Ultraviolet (UV) light decontamination technique has been explored for decontaminating water, food and surfaces and has been shown to provide rapid and effect inactivation of microorganism through a physical process. The aim of this study was to investigate the efficiency of a UV appliance on selected microorganisms. Freshly prepared inoculum of Escherichia coli, Staphylococcus aureus (NCTC 10656), Salmonella Typhimurium (NCTC 13348) and MS2 bacteriophage (ATCC® 15597B1™) surrogate of SARS-CoV-2 virus (Coronavirus) were individually spread on a square shaped stainless steel coupons (100 x 100 x 1 mm) and allowed to dry in a safety cabinet overnight. After drying each stainless-steel coupon was subjected to UV treatment (UV dose ranging between 25.5 mJ/cm2 and 31.4 mJ/cm2). Microbial population before and after UV treatment was enumerated using both selective and non-selective media for each microorganism. The results show that the exposure of stainless-steel surface inoculated with E. coli, S. aureus, S. Typhimurium and MS2 bacteriophage at 30 seconds UV treatment resulted in a reduction of 99 % of E. coli (dose of 25.5 mJ/cm2), 99.9 % of S. aureus (dose of 26.2 mJ/cm2) and 90 % of S. Typhimurium (dose of 28.0 mJ/cm2). The reduction of 99.9% of MS2 bacteriophage was observed with 30 seconds UV treatment (dose of 31.4 mJ/cm2). Average log reduction recorded using counts on selective media were 2.2, 3.4 and 1.8 Log CFU/coupon for E. coli, S. aureus and S. Typhimurium respectively. For MS2 phage a 3.0 Log PFU/coupon was recorded. In conclusion the study reveal that 30 sec of UV treatment is effective for decontaminating stainless steel surface from E. coli, S. aureus, S. Typhimurium and SARS-CoV-2 Virus Surrogate