Virulence factors and strain similarity of Staphylococcus aureus from a dairy farm demonstrate an increased risk of environmental transmission

Abstract

Staphylococcus aureus is a highly adaptable microorganism that harbors virulence factors driving its pathogenicity, affecting animals and humans. Forty S. aureus isolates were collected from a dairy farm operation and were subjected to several phenomics, genomics, and proteomics tests, including antimicrobial susceptibility, biofilm evaluation, strain typing for isolate-relatedness determination, and enterotoxin production. Further characterization involved whole genome sequencing (WGS) and protein detection using mass spectrometry on a subset of isolates (enterotoxin-positive and enterotoxin-negative). All isolates were susceptible to the tested antibiotics except for Gatifloxacin (GAT), for which 100 % displayed intermediate resistance. All isolates produced biofilms, with a noticeable surge at 48 h compared to 24 h (p < 0.001). Additionally, 10 % of the isolates (n = 4) produced enterotoxins associated with human infections. Strain typing via infrared biotyping (IRBT) categorized the 40 isolates into six distinctive groups, indicating close relationships among S. aureus recovered from different samples, demonstrating a movement of the organism within the farm. Genomic characterization of enterotoxin-positive and enterotoxin-negative isolates identified two sequencing types, ST151 and ST351, accompanied by spa types t529 and t9001. Genomics and proteomics analyses revealed various virulence factors, encompassing cytolytic toxins, immune evasion mechanisms, extracellular matrix (ECM)—binding proteins, proteases, enterotoxins, and chromosomal point mutations. In addition to virulence factors, this study shows how this bacterium moves around the farm, potentially becoming an environmental pathogen, increasing the risk of transmission and infection for humans and animals.