Authors: Brooklyn Matthews, Andrew Rowley, Michael Salas, Shaun Kader
Mentors: Michele Culumber, Daniel Clark
Insitution: Weber State University
Paucilactobacillus wasatchensis causes significant product loss in the dairy industry by causing gas build-up in packaging, and slit-crack defects in the cheese. By invitation, we tested a cheese manufacturing plant in northern Utah for Plb. wasatchensis in their creamery based on reports of puffed packages of aged cheese. We were allowed to swab several locations in the production area where contamination with Plb. wasatchensis was possible. Swabbed areas included the areas exposed to milk before and after pasteurization, floor drains, the cheese vat, curd cutters, cheddaring table, and packaging environment. Samples of raw milk, fresh curds, and gassy cheese were also collected. Swabs taken from surface samples were vortexed in 1 mL sterile saline solution. The solution was diluted and plated on deMan, Rogosa, and Sharpe agar with 1% ribose (MRS+R) agar. All agar plates were incubated anaerobically for 1 week. Enrichment cultures for Pbl. wasatchensis were also made by inoculating 0.1 mL of the saline rinse from each swab in MRS+R broth, and incubated for 2 days. After growth, were diluted and plated on MRS+R agar. After 1 week of incubation, we selected small (~1 mm), slow-growing colonies that were morphologically similar to Pbl. wasatchensis. The 16S rRNA gene and N-acetyltrasferase gene were amplified using PCR primers specific for Pbl. wasatchensis. Positive Pbl. wasatchensis isolates were found on the handle of the cheese cutter and in the final cheese product showing a gas defect. Our finding suggests that Pbl. wasatchensis is a potential contaminant in the creamery, and though only found in one location, may exist throughout the facility at unculturable levels. Further studies will use molecular techniques to identify Pbl. wasatchensis throughout the facility to identify bacterial DNA instead of live cells, which may more accurately represent the presence of this fastidious organism.