Comparison of BIOGRAM and commercial microdilution antimicrobial susceptibility test systems

The BIOGRAM (Difco Laboratories, Detroit, Mich.) system, which is designed to calculate MICs from disk diffusion zone diameters, was compared with two commercial microdilution antimicrobial susceptibility systems. A total of 111 clinical isolates were evaluated with each test system. Six additional isolates were tested in a comparison between BIOGRAM and Sceptor (Johnston Laboratories, Inc. Towson, Md.) systems. BIOGRAM demonstrated an overall correlation with the Sceptor microdilution method of 95.7% for 1,287 organism-antimicrobial susceptibility combinations. The BIOGRAM and UniScept (Analytab Products, Inc., Plainview, N.Y.) systems were in agreement in 90.3% of 1,048 organism-antimicrobial susceptibility combinations tested. All methicillin-resistant staphylococci were detected by the standard disk agar diffusion method used with the BIOGRAM system. The BIOGRAM system provides an acceptable alternative to these commercial systems for the determination of quantitative susceptibility.