sprA (USA300HOU_nc0013) was identical in the experimental strains, but different from TCH1516 (note that this feature is not annotated in the FPR3757 genome, but the sequence exists as intergenic and is 100% identical to the TCH1516 sequence). Also, both experimental strains have a 5-nucleotide deletion in the set gene, which encodes a putative superantigen protein. Six indels were identified in A2-VISA that were not present in A1-VSSA,suggestingthatoneormoreofthesemutationsmaybe responsible in whole or in part for the VISA phenotype and daptomycinnonsusceptibility(Fig.2),underthehypothesesthatA1VSSA and A2-VISA were isogenic strains derived from the same founder population. There was a single nucleotide frameshift deletionintheblaZgene(pUSA300HOUMR0011)onthelargeplasmid (NC_010063), which supports the loss of beta-lactamase activity in A2-VISA. Multinucleotide indels were confirmed in the housekeeping sigma factor rpoD, the tetrahydrofolate synthase gene folC, an M20D subfamily peptidase, a PP2C protein phosphatase, and the peptidylprolylisomerase prsA2 (see Fig. 2 for locustagsandbasechanges).Twoofthesewerein-framemutations (PP2C and folC) that would presumably not entirely eliminate translation of these genes, and three were frameshift mutations (rpoD, prsA2, and M20D peptidase). The folC mutation would putativelyresultinthedeletionoftwoaminoacids,isoleucineand aspartate. The insertion mutation in PP2C was a replication of 6 nucleotides,resultinginduplicationoftheaminoacidsglutamate and aspartate (ED) (Fig. 2). It is likely that the M20D peptidase and PrsA2 protein would be nonfunctional, since the frameshifts occurredinthemiddleoftheopenreadingframes.However,since the rpoD deletion affected only the last 4 amino acids at the C terminus of the protein, it is unlikely that this mutation is deleterious,asthisisputativelyanimportantsigmafactorforS.aureus,
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