Bacteriophage Sb-1 has been extensively used for therapy of various human Staphylococcus aureus infections in post-Soviet countries. In presented work, we expanded its host range. The original Sb-1 phage lysate was active against 22/25 (88%) methicillin-resistant S. aureus (MRSA) strains. Sb-1 was then adapted by multiple passages through the three resistant strains. The resulting bacteriophage lysate was designated Sb-1M. The efficiency of Sb-1 and Sb-1M plating was tested on 93 diverse global MRSA isolates. Eighty-one of these (87.1%) were susceptible to original Sb-1, while 89 strains (95.7%) were susceptible to Sb-1M. The full genomes of Sb-1 and Sb-1M and their single-plaque variants were then sequenced to look into genomic changes that could contribute to this marked broadening of host range. Analysis of Sb-1M single-plaque clones demonstrated that 10% of them had expanded host range. Further analysis revealed that Sb-1 genome has at least two hyper variable loci. While Sb-1M grown on a resistant strain clearly shows a single dominant genotype correlating with expanded host range, four more minor genotype variants were identified.