Whole genome sequence analysis of multi-drug resistant and biofilm-forming Staphylococcus haemolyticus isolatedfrom bovine milk

Abstract

Background Milk is an excellent growth medium for microorganisms due to its nutritive composition. Microorganisms have been implicated in bovine mastitis (BM) in dairy cows as well as causing infections in animals and humans. Despite extensive endeavours to manage BM, this condition continues to persist as the most prevalent and economically burdensome problem affecting dairy cattle on a global scale. Non-aureus staphylococci (NAS) species such as Staphylococcus haemolyticus, S. epidermidis, and S. xylosus are currently the predominant microbiological agents identified as the main cause of subclinical udder infections and are also considered opportunistic pathogens in cases of clinical mastitis in dairy cows. Therefore, it is crucial to elucidate the genetic profile of these species. The primary objective of this study was to characterise three phenotypically determined multidrug-resistant NAS environmental strains (NWU MKU1, NWU MKU2, and NWU MKS3) obtained from dairy cows milk via whole-genome sequencing.

Results The results confirmed that the three isolates were S. haemolyticus with genome sizes of 2.44, 2.56, and 2.56 Mb and a G + C content of 32.8%. The genomes contained an array of antibiotic resistance genes that may potentially confer resistance to a range of antibiotic classes, such as macrolides, fluoroquinolones, aminoglycosides, cephalosporins, tetracyclines, peptides, and phenicol. Furthermore, all the genomes carried virulence genes, which are responsible for several functions, such as adhesion, enzyme and toxin production. The genomes of these organisms contained signatures encoding mobile genetic elements such as prophages and insertion sequences.

Conclusion These findings indicate there is a need for diligent monitoring with improved management practices and quality control strategies on farms to safeguard milk production systems and human health.