Elevated Staphylococcus Ceftriaxone MICs are an Etest Artifact

Elevated Staphylococcus ceftriaxone MICs are an Etest artifact.

TO THE EDITOR— The recent publication by Pickering et al [1] described a collection of methicillin-susceptible Staphylococcus aureus (MSSA) that displayed elevated ceftriaxone minimum inhibitory concentrations (MICs) when tested by Etest (bioMerieux, Durham, North Carolina) gradient diffusion and would have been called “Resistant” to ceftriaxone based on previous Clinical and Laboratory Standar...

Polymyxin B Etest Fails to Distinguish Carbapenem-resistant Enterobacteriaceae with Elevated Polymyxin B MICs

Evaluation of Etest to determine tigecycline MICs for Enterobacter species.

Tigecycline is often one of the few therapeutic options for infections by multidrug-resistant Gram-negative bacteria. Therefore, accurate MIC testing is critical. Since in many laboratories tigecycline is not included in the routine panel of antibiotics for susceptibility testing, tigecycline MICs are frequently determined by Etest. However, previous studies have shown that tigecycline MICs det...

Evaluation of Etest method for determining posaconazole MICs for 314 clinical isolates of Candida species.

The performance of the Etest for posaconazole (SCH 56592) susceptibility testing of 314 isolates of Candida spp. was assessed against the National Committee for Clinical Laboratory Standards (NCCLS) microdilution broth method. The NCCLS method employed RPMI 1640 broth medium, and MICs were read after incubation for 48 h at 35 degrees C. MICs were determined by Etest for all 314 isolates with RP...

High concentrations of manganese in Mueller-Hinton agar increase MICs of tigecycline determined by Etest.

MICs of tigecycline determined by Etest were 4 to 12 times (three ATCC strains) and 2 to 8 times (50 clinical isolates) higher in Mueller-Hinton agar from Merck than in Mueller-Hinton agar from either Oxoid or Difco. This was related to a much higher concentration of manganese in the medium from Merck.