Inhibition of Listeria monocytogenes by Broth Cultures of Surface Microbiota of Wooden Boards Used in Cheese Ripening

Listeria monocytogenes is a significant concern in cheese production. It has been assumed by some that wood surfaces pose a greater risk for pathogen contamination during cheese production. The goal of this study was to evaluate the effect of the microbiota obtained from wooden boards used in cheese ripening on the growth of Listeria monocytogenes. Bacterial communities from the surface of wooden boards obtained from cheese-ripening facilities were inoculated into tryptic soy broth (TSB) and incubated at 11 °C for 48 h. These communities (108 CFU/mL stationary phase cells) were co-incubated with 104–105 CFU/mL L. monocytogenes 2203 at 11 °C for up to eight days. At various times, samples were removed, diluted in sterile saline and plated on modified Oxford agar. Bacterial communities from each of the five boards from three different facilities significantly inhibited growth of L. monocytogenes in vitro, compared to growth of L. monocytogenes 2203 alone. Using 16S rRNA analysis, we identified sequences belonging to the genera Carnobacterium, Leuconostoc and Staphylococcus as the most abundant in the communities grown in TSB. Leuconostoc mesenteroides and Staphylococcus equorum isolated from the most inhibitory community significantly inhibited growth of L. monocytogenes in TSB at 11 °C, compared to growth of L. monocytogenes 2203 alone. These findings suggest that some members of the complex microbial communities on wooden boards in cheese aging facilities might inhibit the growth of L. monocytogenes.