Evaluation of the OSIRIS video reader system for disk diffusion susceptibility test reading.
OBJECTIVE
The objective of this study was to compare the performance of the OSIRIS video-assisted reading system for disk diffusion susceptibility testing with conventional manual reading.


METHODS
Prospectively collected clinical isolates (n = 119) and isolates with well-characterised resistant mechanisms, including extended-spectrum (ESBL) or inhibitor-resistant TEM (IRT) beta-lactamases producing Enterobacteriaceae (80), methicillin-resistant Staphylococcus aureus (MRSA) (16) and vancomycin-resistant enterococci (14) were studied using the National Committee for Clinical Laboratory Standards disk-diffusion technique. The OSIRIS reading (inhibition zone in mm) was compared with manual reading (reference value).


RESULTS
Essential agreement (< or =3 mm discrepancy with manual reading) was 91.6% in routine isolates and 94.8% in those with well-characterised resistant mechanisms, respectively. Overall agreement for susceptibility testing interpretation was slightly higher in the former (95.5%) than in the latter (93.2%) group. The presence of ESBL enzymes enhanced variations of measurements due to synergy among amoxicillin-clavulanate and cephalosporins, as a consequence of closer disk placement. The poor growth characteristic of enterococci affected the video reading; on the other hand, there was a high performance with MRSA isolates. Combining all interpretative results, 4.1% minor, 1.0% major and 2.8% very major errors were observed.


CONCLUSIONS
The OSIRIS system is a useful tool for the reading and interpretation of inhibition zone sizes in disk diffusion susceptibility testing.
Sánchez
M A
MA
Servicio de Microbiología, Hospital Ramón y Cajal, 28034-Madrid, Spain.
Sánchez del Saz
B
B
Loza
E
E
Baquero
F
F
Cantón
R
R
D000900:Anti-Bacterial Agents / Q000494:pharmacology*; D004058:Diffusion; D004755:Enterobacteriaceae / Q000187:drug effects* / Q000254:growth & development; D016983:Enterococcus / Q000187:drug effects* / Q000254:growth & development; D006801:Humans; D007091:Image Processing, Computer-Assisted; D007769:Lactams; D016106:Methicillin Resistance; D008826:Microbial Sensitivity Tests / Q000379:methods*; D011446:Prospective Studies; D012016:Reference Values; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D013210:Staphylococcus / Q000187:drug effects* / Q000254:growth & development; D020713:Vancomycin Resistance; D014741:Video Recording; D018440:beta-Lactam Resistance
D000900:Anti-Bacterial Agents; D007769:Lactams