Dysregulation of mprF and dltABCD expression among daptomycin-non-susceptible MRSA clinical isolates.
In small series or individual reports, SNPs within the mprF ORF and dysregulation of its expression in Staphylococcus aureus have been linked to daptomycin resistance (DAP-R) via a proposed gain-in-function mechanism. Similarly, dysregulation of dltABCD has also been associated with DAP-R.



Using 22 well-characterized, isogenic daptomycin-susceptible (DAP-S)/DAP-R clinical MRSA strain pairs, we assessed potential relationships of the DAP-R phenotype with: (i) regulation of mprF transcription; (ii) regulation of dltABCD transcription; (iii) expression of the two-component regulatory system, graRS (upstream regulator for both mprF and dltABCD transcription); (iv) SNPs within the graRS promoter or its ORF; and (v) altered mprF transcription and lysyl-phosphatidylglycerol (L-PG) synthesis.



Enhanced expression of mprF occurred with SNPs in highly distinct and well-chronicled MprF domain 'hot spots' and rarely occurred without such mutations. Increased expression and/or dysregulation of mprF and dltABCD were not uncommon in DAP-R strains, occurring in 27% of strains for each gene. In these latter strains, neither graRS expression profiles nor polymorphic sequences within the graRS promoter or ORF could be significantly linked to altered transcription of mprF or dlt.



Although graRS can co-regulate mprF and dltABCD expression, loci outside of this regulon appear to be involved in dysregulation of these latter two genes and the DAP-R phenotype. Finally, DAP-R strains exhibiting significantly altered mprF transcription profiles produced significantly increased levels of L-PG.
Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA, USA The David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Arnold S
AS
Bayer
Division of Infectious Diseases, Los Angeles Biomedical Research Institute at Harbor-UCLA Medical Center, Torrance, CA, USA The David Geffen School of Medicine at UCLA, Los Angeles, CA, USA.
Nagendra N
NN
Mishra
Department of Microbiology, Geisel School of Medicine at Dartmouth, Hanover, NH, USA.
Ambrose L
AL
Cheung
Spero Therapeutics, Cambridge, MA, USA.
Aileen
A
Rubio
School of Bioresources and Bioscience, Chung-Ang University, 4726 Seodong-daero, Daedeok-myeon, Anseong-si, Gyeonggi-do 456-756, Republic of Korea soojin@cau.ac.kr.
Soo-Jin
SJ
Yang
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D001426:Bacterial Proteins / Q000096:biosynthesis* / Q000235:genetics; D017576:Daptomycin / Q000494:pharmacology*; D024881:Drug Resistance, Bacterial; D020869:Gene Expression Profiling; D015964:Gene Expression Regulation, Bacterial; D055624:Methicillin-Resistant Staphylococcus aureus / Q000187:drug effects* / Q000235:genetics*; D020641:Polymorphism, Single Nucleotide; D011401:Promoter Regions, Genetic; D014158:Transcription, Genetic
D000900:Anti-Bacterial Agents; D001426:Bacterial Proteins; D017576:Daptomycin