TABLE 1

Daptomycin and vancomycin MICs of strains 8019 (daptomycin susceptible) and 5938 (daptomycin resistant) in Mueller-Hinton agar plates containing various beta-lactams at selected concentrations by Etestc

Beta-lactam (mg/liter)bMIC (mg/liter)
Strain 8019Strain 5938
DAPVANDAPaVAN
None0.38>25610>256
CPT (1)0.38>2566>256
CPT (2)0.38>2562>256
CPT (4)0.25>2562>256
CPT (8)0.19>2560.7524
AMP (25)0.25>2566>256
AMP (50)0.25>2566>256
PIP (20)0.38>2566>256
CRO (20)0.38>2566>256
CZL (20)0.38>2566>256
  • a VRE strain 5938 has been previously reported as initially having a DAP MIC of 192 mg/liter by Etest. However, upon retrieval of this isolate from the freezer, the DAP MIC by Etest was decreased to 10 mg/liter, consistent with the instability of DAP nonsusceptibility previously reported.

  • b CPT, ceftaroline; AMP, ampicillin; PIP, piperacillin; CRO, ceftriaxone; CZL, cefazolin; LIN, linezolid.

  • c Mutation differences between isogenic strains 8019 and 5938 have been previously characterized by whole genome sequencing (6). MICs (mg/liter) of strains 8019 and 5938 to various antibiotics are as follows: CPT, >32; AMP, >64; PIP, >64; CRO, >64; CZL, >64; LIN, 2.