Reservoirs of spoilage fungi in the built environment of cultured dairy facilities vary by season and location

ABSTRACT The processing environment is a source of spoilage fungi in cultured dairy products. However, fungi within the built environment (i.e ., non-food contact and architectural structures) of dairy processing facilities have not been well characterized. This study identified the seasonal and spatial variations in fungal identity, relative abundance, and diversity within the built environment of three cultured dairy facilities. Furthermore, we compared fungal genera in spoiled cultured dairy products to fungal genera in their facility’s built environment. We used internal transcribed spacer sequencing to characterize fungi from 119 environmental surfaces in three cultured dairy facilities and from 154 spoiled cultured dairy products manufactured in those facilities. The fungal genera Aureobasidium , Candida, Cladosporium, Mucor, Penicillium , and Yarrowia were identified in both spoiled products and their corresponding built environment. The fungal diversity on environmental surfaces varied (0–3.98, Shannon diversity; 0–176, Chao1 diversity) and was significantly ( P < 0.01) different among Production Area (Warehouse, Raw, Filling, and Post-Pasteurization) and Season. Furthermore, the abundance of several fungal genera related to dairy product spoilage was significantly different ( P < 0.05) among Production Area, Season, Object Type, and Facility. Network analysis further demonstrated distinct fungal composition among Production Areas within each facility. For Object Types, the relative abundance of spoilage fungal genera varied from 0% to 100%, and yeast and mold (YM) counts ranged from 0 to 8.27 log 10 CFU/sponges. Swab sites with elevated relative abundances of spoilage genera and YM counts were identified as fungal reservoirs, which could serve as point sources for product contamination. IMPORTANCE Spoilage of cultured dairy products from fungal contamination results in food waste and economic loss. Fungi from the facility’s built environment can be transferred to the product via air currents, water droplets, or through surface contact. Our year-long study identified overlap among fungal genera on environmental surfaces and spoiled products in three cultured dairy facilities, suggesting an overlap between environmental presence and product contamination. Furthermore, fungi was spatially differentiated within each facility, with some specific sites serving as potential point sources for product contamination. These results support the need for hygienic zoning in food processing facilities. Our work confirms the importance of environmental surface swabbing as a tool to locate potential fungal reservoirs in the built environment, which can aid targeted interventions against spoilage fungi in dairy processing facilities.