Genetic Diversity of Staphylococcus Aureus Isolates From Subclinical Bovine Mastitis by Inter-Simple Sequence Repeat Oligonucleotides

Staphylococcus aureus is one of the main etiological agents of bovine mastitis, affecting animal health and causing significant economic losses in dairy farming. The genetic variability of this species is associated with virulence factors and antimicrobial resistance, complicating the control and treatment of infections. This study aimed to assess the applicability of ISSR oligonucleotides as an alternative tool for genetic diversity analysis of S. aureus . Thirty isolates from milk samples of cows with subclinical mastitis were used, exhibiting multidrug resistance to antimicrobials and biofilm-forming capacity. The analysis consisted of applying 52 primers from the ISSR UBC Primer Set #9, with temperature gradient tests to optimize annealing. Amplification profiles were evaluated using GelAnalyzer 23.1.1 software and organized into binary matrices. Diversity studies and biometric analyses were conducted using GENES software, estimating genetic dissimilarity through the arithmetic complement of Jaccard's index (Sj). Cluster analysis employed the UPGMA hierarchical method, with results represented in dendrogram and scatter plot formats. Of the primers tested, 48% generated polymorphic patterns, 15% displayed monomorphic bands, 33% produced no amplification, and 4% were inconclusive. The 25 polymorphic primers revealed substantial genetic variability among isolates and wide geographic dispersion, with no clustering restricted by municipality. The absence of defined geographic structuring corroborates the hypothesis of intermunicipality dissemination of the pathogen, possibly influenced by animal movement and lack of uniform biosecurity protocols. The significant presence of polymorphisms demonstrates that ISSR oligonucleotides are viable for genetic characterization of S. aureus , providing support for epidemiological surveillance and management of strains with clinical and zootechnical relevance.