Genome data cross-contamination versus interdomain recombination: Equus caballus and Mus musculus genetic loci in the insertion sequence-rich genomes of two clonally related methicillin-resistant Staphylococcus aureus strains from China.

BACKGROUND

Methicillin-resistant Staphylococcus aureus (MRSA) represents a significant global health threat, responsible for infections in both humans and animals. Determining genetic patterns associated with the genome plasticity of MRSA is critical for predicting the evolutionary trajectories of its emerging pathogenic clones.

RESULTS

The specific genetic loci of the MRSA strains WH3018 and WH9628 from Wuhan, China, ranging in size from 399 to 3,622 base pairs, were determined to be highly homologous (DNA identity: 90.95-100%) to corresponding chromosomal regions from Equus caballus and Mus musculus in the GenBank database. These eukaryotic-associated loci included the microsatellite DNAs or Y chromosome-specific regions from E. caballus, or 45 S-28 S ribosomal RNA/H19 loci from M. musculus, all exhibiting recurrent patterns across the genomes of both MRSA strains. The SplitsTree and RDP4 analyses did not reveal significant recombination signals for the eukaryotic-associated loci that had mimicked interdomain recombination events in the MRSA strains WH3018 and WH9628. The G + C content of these loci (47.6-65.0%) was notably higher than that of the S. aureus reference genome (32.5%). Furthermore, the MRSA genomes showed a significantly larger number and greater diversity of insertion sequences (ISs) (38 ISs per genome) compared to the S. aureus reference genome (16 ISs). Additionally, these genomes also exhibited an extensive decay of prophages and the accumulation of pseudo-transposases.

CONCLUSIONS

The recurring patterns of the eukaryotic-associated loci strongly suggested genome data contamination across the genomes of the MRSA strains WH3018 and WH9628. These MRSA genomes likely underwent extensive prophage decay and an increased proliferation of pseudo-transposases.