Whole Genome Sequencing, Annotation and Comparative Analysis of a Hospital Isolated Staphylococcus aureus Strain H3: New Insights about Its Architecture, Virulence Factors and Antimicrobial Resistance

Background and Objectives Staphylococcus aureus is a leading cause of hospital-acquired infection worldwide, yet whole-genome data from Iraqi clinical isolates are almost absent. We report the first draft genome and comparative genomic analysis of S. aureus strain H3, a hospital clinical isolate from Iraq. Materials and Methods The genome was sequenced using Illumina short reads, assembled de novo, and annotated with the BV-BRC Comprehensive Genome Analysis service. Resistance, virulence and phylogenomic placement were profiled and compared with the reference strain NCTC8325 (NZ_CP088157) and representatives of the major clonal complexes. Results The 2,574,151-bp draft genome (87 contigs; N50 67,989 bp; L50 11; G+C 32.84%) contained 2,438 protein-coding sequences, 55 tRNAs and 3 rRNAs, with coarse and fine consistency of 100% and 99.9%. Specialty-gene profiling identified 52 antimicrobial-resistance genes, 88 virulence factors, 122 transporters, 27 drug targets and 8 metal-resistance genes. Against NCTC8325, H3 differed by 20,946 variants (20,546 SNPs and 400 indels), indicating marked divergence and placing H3 outside the CC8 clade as a separate lineage. Its virulence repertoire included Panton–Valentine leukocidin, α-, β-, γ- and δ-haemolysins, the ica biofilm operon, adhesins, superantigens and a complete Type VII secretion system. Conclusion S. aureus H3 is a divergent, virulent, hospital-adapted lineage, providing a genomic baseline for future epidemiological studies of S. aureus in Iraq and the Middle East.