Comparison of antimicrobial susceptibilities to 10 drugs and 2 drug mixtures in the absence or presence of the Cfr methyltransferase in E. coli AS19 and S. aureus RN4220 strains

Bacteriumcfr carriageAdditional resistance gene(s)aMIC (μg/ml)b,c
E. coli AS190.0310.01520.50.254840.
E. coli AS19::pBluescript II SK(+)blaTEM-1160.0310.01520.50.254840.
E. coli AS19::pBamHIΔcfrblaTEM-1160.0310.01520.50.254840.
E. coli AS19::pBglIIcfrblaTEM-11640.125128161664≥5121680.250.50.25
S. aureus RN42200.0630.03140.≤0.063
S. aureus RN4220::pSCFS3cfrfexA≥12811284142562561280.252≤0.063
S. aureus RN4220::pSCFS1cfrerm(33), spc, lsa(B)≥128≥1281288482566432≥1282≤0.063
S. aureus RN4220::pSCFS2fexA0.0630.03140.≤0.063
  • a Additional resistance genes located on the same plasmid/cloning vector: blaTEM-116 (resistance to ampicillin), fexA (resistance to phenicols), erm(33) (inducible resistance to macrolide, lincosamide, and streptogramin B antibiotics), spc (resistance to spectinomycin), and lsa(B) (low-level lincosamide resistance).

  • b Antimicrobial agents are abbreviated as follows: TIA, tiamulin; VAL, valnemulin; VIR M1, virginamycin M1; VIR, virginiamycin; Q-D, quinupristin/dalfopristin; LZD, linezolid; CLI, clindamycin; CHL, chloramphenicol; FFC, florfenicol; ERY, erythromycin; AIV, acetylisovaleryltylosin; TEL, telithromycin.

  • c Breakpoints for susceptibilities of staphylococci (according to CLSI document M100-S14): quinupristin/dalfopristin, ≤1 mg/liter; linezolid, ≤4 mg/liter; chloramphenicol, ≤8 mg/liter; clindamycin, ≤0.5 mg/liter. There are no approved CLSI breakpoints for staphylococci and tiamulin, valnemulin, virginiamycin M1, virginiamycin, or florfenicol.