Association between cell growth and vancomycin resistance in clinical community-associated methicillin-resistant...

We investigated the association between the rate of cell growth and vancomycin (VAN) resistance by comparing the genomic and phenotypic characteristics of different sized colonies isolated from a single origin.

Vancomycin-intermediate Staphylococcus aureus (VISA) strain TMUS2136 was isolated from the pus of a patient with a brain abscess and a chronic subdural abscess. This strain grew slowly and formed colonies poorly on agar plates within 24 h of incubation. However, variously sized colonies were observed after 48 h of incubation. We isolated five strains from different sized colonies and compared their VAN susceptibility and genomic sequences using next-generation sequencing.

The five strains showed different rates of growth and susceptibilities to VAN (range of MIC after 48 h of incubation; 3-5 mg/L), and slower growing strains tended to be more VAN resistant. Deletion of the spdC gene and SNPs in the sarA gene was confirmed in all five strains and six SNPs in other genes (including mreC, hssS, prs, SA2339, sun, and SA1132) were confirmed when comparing the five strains.

Deletion of the spdC gene, a novel virulence factor of S. aureus, and SNPs in the sarA gene may be associated with VAN resistance. It was hypothesized that any of the six genes in which SNPs were detected could affect cell growth rate and VAN resistance in slow-VISA strains.