Genetic diversity of iron acquisition systems of Staphylococcus aureus associated with bovine mastitis

Staphylococcus aureus is a major pathogen in humans and animals that relies on various iron acquisition systems during infection. This study analyzed the genetic diversity and distribution of iron uptake genes in 255 S. aureus isolates from eight clonal complexes (CCs) associated with bovine mastitis, collected from 19 countries. Forty-one genes from seven iron systems (including sirABC, sbnA-I, fhuBCG, fhuD, htsABC, sfaA-D, sstA-D, isdA-I, fepABC, tatAC) and the regulatory gene fur were investigated. A genome with < 95% completeness was excluded. CCs were determined using eBURST, and phylogenetic relationships were assessed using the Maximum Likelihood method (Mega-X). Genetic diversity was analyzed using DNAsp. All CCs harbored most iron acquisition genes, with no system entirely absent, highlighting their essential roles. Phylogenetic patterns aligned with MLST markers, except for distinct clustering in sbnA-I and sirABC (CC8, CC398, CC97), and shared grouping of CC8 and CC97 in htsABC and sstABCD were observed. High diversity was observed in htsB, sirB, isdB, isdH, and sstABCD. Shared haplotypes suggest international clonal transmission. CC398 showed fewer haplotypes, likely because of its broad host range, whereas cattle-adapted CC151 and CC97 showed greater diversity. These findings enhance our understanding of S. aureus epidemiology and support improved veterinary and public health measures.