However, this did not result in interpretation discrepancies (Table 2). Most important, on-screen adjusted automation of disk diffusion readings did not result in an increased frequency of susceptibility categorisation errors. The results of this study showed no major and very major discrepancies occurring with on-screen adjusted Sirscan readings

KPT-8602 cell line when compared to manual measurements serving as the gold standard. Other authors found low numbers of major and very major errors with the Sirscan system as well [12, 13]. Isolates with confirmed resistance mechanisms such as ESBL, AmpC, carbapenemases, VRE, or MRSA were reliably detected except for two isolates showing inhibition zone diameters close to the EUCAST breakpoint. However, both isolates would have been missed by manual reading, too. Reproducibility and precision check details of diameter measurements are critical for AST interpretation and antimicrobial therapy. Previous investigations have focused on the correlation of manual and automated measurements using Bcl-2 inhibitor systems like Sirscan, OSIRIS, BIOMIC, or Oxoid Aura [12–16,

20]. While correlation of manual and automated systems is well established, we here used a fully automated system to assess, if automated reading is principally able to decrease standard deviation of measurements and, thus, can increase precision. This is of particular importance given the changes in recent EUCAST and, in part, CLSI AST guidelines to decrease or even abandon the intermediate AST zone [19]. Investigator dependence of manual measurements with the disk diffusion method is partly due to non-standardised conditions such as ambient light, angle of vision, reading plates from top or bottom, or physical and mental condition of the investigator. The Sirscan analysis software reads under standardised light, positioning and background conditions. The lack or downsizing of the intermediate category by CLSI and/or EUCAST 2011/12 guidelines enhances

the probability of major and very major errors of repeat measurements since susceptible and resistant categories lie directly adjacent to each other [17–19]. Standardisation Glutathione peroxidase of measurements with concomitant lower standard deviations will facilitate consistent AST reports for repeatedly tested strains, or for ASTs of one strain isolated from multiple patient samples. The reproducibility of fully automated Sirscan readings without human interaction (on-screen adjustments) was significantly higher compared with manual calliper measurements. The average standard deviation for repeat measurements of E. coli ATCC 25922 and S. aureus ATCC 29213 inhibition zones was reduced by half using the fully automated reading mode. If, however, Sirscan readings were adjusted on-screen, standard deviations were not significantly lower (Table 3). For P.