Microbiological Risks Associated with Hot-Drinks Vending

Abstract

The UK vending industry has received little microbiological attention. Although reported cases of gastroenteritis related to hot-drinks vending are rare, there is evidence of microbial contamination and one reported outbreak of gastroenteritis concerning consumption of hot chocolate. This thesis examines the microbiology of hot-drinks vending operations, the effect of commonly used cleaning protocols on the microbial load of vending components and vended hot drinks and assesses the microbiological risks associated with hot-drinks vending machines. A survey of vending operators identified three main cleaning methods. Laboratory validation of these methods was conducted using vending machine mixing bowls, artificially soiled with hot chocolate powder and Bacillus cereus or Staphylococcus aureus. Detergent, detergent/sanitiser and dishwasher protocols all achieved significant (ANOVA, p <0.05), 3 log reductions. No significant (Tukey' pairwise comparison, p <0.05) difference was observed between the protocols. The development of a microbial population within a commercial hot-drinks vending machine was investigated. The machine vended ≥ 50 hot chocolate drinks per day over 19 weeks and was cleaned using a weekly, detergent-based protocol. Over the first 7 – 10 weeks a significant (ANOVA, p <0.05) increase in the microbial load of the mixing bowl, dispense point and vended drink was observed, reaching a „quasi-steady state‟ until the end of the study. Weekly cleaning significantly (ANOVA, p <0.05) reduced the microbial load of the mixing bowl and drink. The microbial load of the drink showed no reduction over nine minutes after vending, suggesting only spores were present. B. cereus was identified using biochemical methods. The presence of B. cereus in the vending powders, machine components and drinks was confirmed using a Polymerase Chain Reaction based assay. Of the 291 isolates tested, 90% were confirmed as B. cereus. Random Amplified Polymorphic DNA analysis indicated that the primary source of contamination in the vended drinks was the drinks powder. However, some isolates were identified within the drinks that were found on the machine components but not the powders. A microbiological risk assessment found the risk of B. cereus gastroenteritis associated with consumption of vended hot chocolate was low, providing machines are maintained appropriately.