Staphylococcus aureus Entrance into the Dairy Chain: Tracking S. aureus from Dairy Cow to Cheese

Abstract

<i>Staphylococcus aureus</i> is one of the most important contagious mastitis pathogens in dairy cattle. Due to its zoonotic potential, control of <i>S. aureus</i> is not only of great economic importance in the dairy industry but also a significant public health concern. The aim of this study was to decipher the potential of bovine udder associated <i>S. aureus</i> as reservoir for <i>S. aureus</i> contamination in dairy production and processing. From 18 farms, delivering their milk to an alpine dairy plant for the production of smeared semi-hard and hard cheese. one thousand hundred seventy six one thousand hundred seventy six quarter milk (QM) samples of all cows in lactation (<i>n</i> = 294) and representative samples form bulk tank milk (BTM) of all farms were surveyed for coagulase positive (CPS) and coagulase negative Staphylococci (CNS). Furthermore, samples from different steps of the cheese manufacturing process were tested for CPS and CNS. As revealed by chemometric-assisted FTIR spectroscopy and molecular subtyping (<i>spa</i> typing and multi locus sequence typing), dairy cattle represent indeed an important, yet underreported, entrance point of <i>S. aureus</i> into the dairy chain. Our data clearly show that certain <i>S. aureus</i> subtypes are present in primary production as well as in the cheese processing at the dairy plant. However, although a considerable diversity of <i>S. aureus</i> subtypes was observed in QM and BTM at the farms, only certain <i>S. aureus</i> subtypes were able to enter and persist in the cheese manufacturing at the dairy plant and could be isolated from cheese until day 14 of ripening. Farm strains belonging to the FTIR cluster B1 and B3, which show genetic characteristics (t2953, ST8, enterotoxin profile: <i>sea</i>/<i>sed</i>/<i>sej</i>) of the recently described <i>S. aureus</i> genotype B, most successfully contaminated the cheese production at the dairy plant. Thus, our study fosters the hypothesis that genotype B <i>S. aureus</i> represent a specific challenge in control of <i>S. aureus</i> in the dairy chain that requires effective clearance strategies and hygienic measures already in primary production to avoid a potential transfer of enterotoxic strains or enterotoxins into the dairy processing and the final retail product.