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Evaluation of the OSIRIS video reader system for disk diffusion susceptibility test reading

2001; Elsevier BV; Volume: 7; Issue: 7 Linguagem: Inglês

10.1046/j.1198-743x.2001.00274.x

1469-0691

Mario Alberto Morales Sánchez, Begoña Sánchez Del Saz, Elena Loza, Fernando Baquero, Rafael Cantón,

Antimicrobial Resistance in Staphylococcus

ObjectiveThe 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.MethodsProspectively collected clinical isolates (n = 119) and isolates with well-characterised resistant mechanisms, including extended-spectrum (ESBL) or inhibitor-resistant TEM (IRT) β-lactamases producing Enterohacteriaceae (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).ResultsEssential agreement (≤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.ConclusionThe OSIRIS system is a useful tool for the reading and interpretation of inhibition zone sizes in disk diffusion susceptibility testing. 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. Prospectively collected clinical isolates (n = 119) and isolates with well-characterised resistant mechanisms, including extended-spectrum (ESBL) or inhibitor-resistant TEM (IRT) β-lactamases producing Enterohacteriaceae (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). Essential agreement (≤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. The OSIRIS system is a useful tool for the reading and interpretation of inhibition zone sizes in disk diffusion susceptibility testing.