Nucleotide substitutions in Staphylococcus aureus strains, Mu50, Mu3, and N315.

A specific phenotype of Staphylococcus aureus strains Mu50 and Mu3 is characterized by thickened cell wall and moderate resistance to vancomycin. The N315 strain is a prototype of methicillin-resistant S. aureus (MRSA), but it is methicillin susceptible, despite carrying the mecA resistance gene. Here, we revised differences in the sequences of Mu50 and N315, referencing that of Mu3 which were assumed to be of one lineage. The 362 ORFs diverse between Mu50 and N315 were picked up, and the corresponding ones in three strains were re-sequenced. This defined 213 ORFs diverse between Mu50 and N315, and 9 between Mu50 and Mu3. The fixed diversities of 174 ORFs (except for 39 silent ORFs from 213), including nucleotide substitution (NSs), frame shift, and truncation were grouped into three major functional categories, which were transport (14.9% in the 174 diverse ORFs), metabolism of carbohydrates (5.7%), and RNA synthesis (9.6%). The other gene categories had small diversities. These gene categories seemed to be functionally decisive for the Mu50-specific characters, the thickened cell wall and moderate vancomycin resistance. All of the diverse genes and the high quality sequence of Mu50 can be viewed at the web site (http://133.5.48.239/VRSA/).