Comparison and evaluation of Osiris and Sirscan 2000 antimicrobial susceptibility systems in the clinical microbiology laboratory.

The Osiris and Sirscan 2000 systems are two semiautomated systems that can be used to read and interpret the results on disk diffusion agar plates. They are both used for determination of susceptibility to antimicrobial agents. The present study compared both systems versus the NCCLS standard method of visual reading with a ruler. Both inpatient and outpatient samples with a total of 315 nonfastidious gram-negative strains were obtained. In total, 3724 organism-antimicrobial agent combinations that fulfilled the NCCLS guidelines for disk diffusion susceptibility testing were evaluated prospectively. The results obtained with both systems in comparison with those obtained by the classical nonautomated means of interpretation were excellent, with correlation coefficients of 0.96 for both systems. The overall agreements for susceptibility interpretation were 96.56 and 96.24% with the Osiris and Sirscan systems, respectively. Very major errors were obtained for 8 (1.07%) and 10 (1.34%) organism-antimicrobial agent combinations with the Osiris and Sirscan systems, respectively. In addition, major errors were obtained for 2 (0.07%) and 6 (0.21%) combinations with the Osiris and Sirscan systems, respectively. Minor errors were obtained for 118 and 124 organism-antimicrobial agent combinations with the Osiris and Sirscan systems, respectively. Overall, both the Osiris system and the Sirscan system are comparable and reliable systems for determination of interpretative categories from the zone diameters of standard disk diffusion test plates.