Bacterial Quality, Prevalence of Pathogens, and Molecular Characterization of Biofilm-Producing Staphylococcus aureus from Korean Dairy Farm Environments

SIMPLE SUMMARY: In this study, we analyzed hygienic indicator bacteria and pathogenic microorganisms (Salmonella spp., Escherichia coli O157:H7, Listeria monocytogenes, Bacillus cereus, Staphylococcus aureus, Clostridium perfringens, Campylobacter jejuni/coli) in Korean dairy farms. As a result, B. cereus and S. aureus were detected in dairy farm environment. Total aerobic bacteria, psychrotrophic bacteria, coliform, and yeasts/molds differed slightly between dairy farms, but a few spots, such as floors, drain holes, and niches, showed high microbial counts in most of dairy farms. Subsequently, we performed RNA-seq analysis on Staphylococcus aureus JDFM SA01 isolated from a milk filter to determine the biofilm formation ability and characteristics. In biofilm, the significant up-regulation of genes encoding surface proteins and genes, which advance the adhesion, might clarify the increased biofilm viability and biomass. Therefore, in this study, spots with high possibility of microbial contamination could be identified in dairy farms and the basis for producing safe milk and dairy products by effective hygiene management against microbial contamination was established. ABSTRACT: Raw milk acts as a mediator of major foodborne pathogenic bacterial infections. However, the sources of pathogens that contaminate milk are often unclear. This study assessed the prevalence of sanitary quality-indicating bacteria (total aerobic bacteria, psychrotrophic bacteria, coliform, and yeast/molds), including seven foodborne pathogens, in a dairy farm environment and processing plant in Korea. The microbiological analysis showed that a few sites, such as vat bottoms, room floors, drain holes, and niches, showed high microbial loads in most dairy farms. Based on quantitative microbial tests, Bacillus cereus was detected in three farms and Staphylococcus aureus was detected in only one farm. Among them, S. aureus JDFM SA01 isolated from a milk filter showed strong biofilm formation and toxicity to the host Caenorhabditis elegans. Subsequently, RNA-seq was performed to characterize the biofilm formation ability of S. aureus JDFM SA01. In biofilms, the significant upregulation of genes encoding microbial surface components and recognizing adhesive matrix molecules promotes adhesion might explain the increased viability and biomass of biofilms. This study provided insight into the prevalence of pathogenic bacteria and microbial contamination levels across dairy farms.