Evaluation of three commonly used cleaning methods for reducing bacterial numbers on hot drinks vending machine mixing bowls artificially contaminated with Bacillus cereus and Staphylococcus aureus

Abstract

During normal operation, mixing bowls in hot drinks vending machines become soiled with drink powders and water, increasing the risk of microbial growth and survival of microorganisms. The efficacy of three different cleaning protocols against artificially contaminated mixing bowls was investigated. Mixing bowls were soiled using hot chocolate powder and a suspension of either Staphylococcus aureus or vegetative Bacillus cereus giving a final bacterial load of 10⁶ cfu/cm², and were cleaned using detergent, detergent/sanitiser and dishwasher-based cleaning protocols. Traditional microbiological methods were used to measure the effect of cleaning. All three cleaning protocols gave a significant (P ≤ 0.05) reduction in bacterial numbers, each achieving approximately a 3-log reduction. No significant or operational differences were observed between the three methods, although the detergent/sanitiser protocol achieved the greatest log reduction. This study demonstrates that a simple, detergent-based cleaning protocol is sufficient to achieve a 3-log reduction in bacterial load of artificially soiled mixing bowls.