Short communication: Virulence profiles of Staphylococcus aureus isolated from bulk tank milk and adherences on milking equipment on Chilean dairy farms

摘要

Staphylococcus aureus is an important intramammarypathogen for dairy cows that also is remarkably importantfor public health. Multiple virulence factors canbe involved simultaneously during the pathogenesis ofa staphylococcal disease, including adhesion proteins,extracellular enzymes, and toxins. The main objectiveof this study was to assess virulence factors that areassociated with cow intramammary infection (IMI) andof human health concern among Staph. aureus isolatesobtained from bulk tank milk (BTM) and adherenceson milking equipment surfaces. A total of 166 Staph.aureus isolates from 23 dairy farms were characterizedaccording to their virulence profiles. For virulence factorsof importance in IMI, the presence of the virulencemarkers thermonuclease (nuc) and coagulase (coa) andvirulence genes such as fibronectin (fnbA) and intercellularadhesion (icaA, icaD) were assessed. For virulencefactors of public health concern, presence of antimicrobialresistance (mecA and mecC) and enterotoxin(sea and seb) genes were analyzed. Among all Staph.aureus isolates, 5 virulence profiles were found; the profilenuc~((+)) coa~((+)) fnbA~((+)) icaA~((+)) icaD~((+)) mecA~((-)) mecC~((-))sea~((-)) seb~((-)) was the most frequently observed (21 outof 23 dairy farms). No differences were found betweenthe virulence profile frequencies of Staph. aureus fromBTM and adherences on milking equipment surfaces.The virulence profiles most frequently observed includedgenes involved in the adherence and biofilm-formingability of Staph. aureus, which could represent a potentialadvantage for the bacterium during the early stagesof IMI colonization and for persistence on surfaces. Ourresults indicate a greater frequency of virulence factorsof importance for IMI pathogenesis than virulencefactors of public health concern, consistent with thedairy origin of isolates. The mecA, mecC, and seb geneswere not observed among Staph. aureus isolates analyzedin this study. However, the sea gene was detectedin 3 Staph. aureus isolated from BTM, thus posing apotential public health threat. Our results emphasizethe importance of understanding the epidemiology anddynamics of Staph. aureus on dairy farms as a tool forthe improvement of udder health and milk safety.