Population dynamics and bidirectional transfer of Listeria monocytogenes and Shiga toxin-producing Escherichia coli during cheese production in wooden vats

Wooden vats are used in the production of some traditional cheeses as the biofilms on wooden vat surfaces are known to transfer large quantities of microbes to cheese. However, the safety of using wooden vats for cheese production remains controversial as the porous structure of wood provides an irregular surface that may protect any attached pathogen cells from cleaning and sanitation processes. On the other hand, the absence of pathogens in wooden vats has been reported in multiple studies and wooden materials have not been associated with foodborne illness outbreaks. The present study determined the survival of Listeria monocytogenes and Shiga toxin-producing Escherichia coli (STEC) during the production of an uncooked pressed cheese in wooden vats as well as their ability to transfer to the wood and then to milk used in subsequent batches of cheese production in the absence of formal cleaning. Results from the study indicate that pathogens inoculated in milk grew during production of the uncooked cheese, but showed limited ability to colonize the wooden vats and contaminate subsequent batches. These results suggest that the risks of using wooden vats to produce cheese is low if the milk is of high microbiological quality.