Evaluation of the Cobas Bact automated system for susceptibility testing of Enterobacteriaceae, Pseudomonas aeruginosa, and Enterococcus faecalis to azlocillin, mezlocillin, and ciprofloxacin compared to NCCLS and DIN standards.

The aim of automated susceptibility testing systems like the Cobas Bact is to provide the clinicians with rapid and reliable results for the care of patients and to decrease the work load in microbiological laboratories. Because data about accuracy on mezlocillin, azlocillin and ciprofloxacin were lacking, we investigated 184 bacterial strains and compared the results of the Cobas Bact susceptibility testing to standardized agar dilution and agar diffusion methods. Essential correlations for all methods compared exceeded 90% for the three chemotherapeutics and all species investigated, with the exception of Pseudomonas aeruginosa. On an average only 1.5% very major errors were observed with the several species of Enterobacteriaceae, whereas P. aeruginosa and Enterococcus faecalis were characterized by the complete absence of very major errors when Cobas Bact was correlated to NCCLS agar diffusion.