Public Health Bacteriology of Commercially Composted Domestic Food and Garden Waste by the 11 Councils in Northern Ireland – Persistence Of Clostridium perfringens and Implications for Local Food Safety

BACKGROUND: New legislation has been introduced in Northern Ireland from April 2017, requiring domestic households to recycle all domestic food waste items. The purpose of this study was to examine the bacteriology of compost derived from this source which is supplied free-of-charge to the public for horticultural use. METHODS: Municipal compost samples were compared microbiologically with commercial garden compost samples, examining total viable count and diversity of bacteria cultivated. RESULTS: The municipal compost had a mean Total Viable Count (TVC) of 1.53 × 10(8) colony forming units (cfu)/ g compost, whereas the commercial garden compost had a mean TVC of 4.5 × 10(7) cfu/g compost. Campylobacter, Salmonella and Listeria were not isolated from any compost. Twenty-three bacterial genera were represented amongst the 46 organisms recovered. Of these, Pseudomonas aeruginosa and Clostridium perfringens were the most clinically significant. DISCUSSION: The application of municipal compost to cultivate non-food plants, such as roses and flowers presents minimal risk, provided safe handling practices are adopted and hands are thoroughly washed and dried afterwards. However, if applied to soil growing food produce, it is important that municipal compost does not enter the food chain without an effective critical control point which would prevent germination of spores of Clostridium perfringens. Risk may be increased in products such as marinades, home canning, home bottling and associated products. These methods of food preparation are common in ethnic Eastern European populations in Northern Ireland, where awareness of risk needs to be increased.