Evaluation of the autoSCAN-W/A rapid system for identification and susceptibility testing of gram-negative fermentative bacilli.
The autoSCAN-Walk-Away (W/A) system for identification and susceptibility testing was evaluated for 400 gram-negative fermentative bacteria by using the API 20E (366 isolates) and/or tube biochemical tests as the reference identification system and a frozen microdilution MIC tray system for susceptibility testing. The W/A system performed well for identification of this group of organisms representing 14 genera and 30 species, showing a sensitivity of 96% and results available in 2 h. Of the 16 misidentifications, 6 were with Serratia liquefaciens. A total of 63 isolates (17%) required further tests to complete the identification, compared with 106 (29%) of the isolates which required additional tests for the API 20E identification. Approximately half (32) of the additional tests with the W/A system were required in order to separate Citrobacter diversus from C. amalonaticus. For susceptibility determinations, the W/A system demonstrated an overall agreement of 93% (4,102 determinations) with 40 major errors (0.98%). However, of the 906 resistant organism-drug combinations in the study, there were 115 very major errors, for a false-susceptibility rate of 12.7% of the resistance determinations. Among these very major errors, 80% occurred with piperacillin and the cephalosporins. The W/A system completed the MIC determinations in 7 h; however, the difficulty in detecting resistance with some antimicrobial agents limited the advantages of the rapid susceptibility testing.
York
M K
MK
Department of Laboratory Medicine, Moffitt Hospital, University of California, San Francisco 94143-0100.
Brooks
G F
GF
Fiss
E H
EH
D001431:Bacteriological Techniques; D003951:Diagnostic Errors; D004352:Drug Resistance, Microbial; D005069:Evaluation Studies as Topic; D005285:Fermentation; D006090:Gram-Negative Bacteria / Q000145:classification* / Q000187:drug effects / Q000378:metabolism; D016905:Gram-Negative Bacterial Infections / Q000175:diagnosis / Q000188:drug therapy / Q000382:microbiology; D006801:Humans; D008826:Microbial Sensitivity Tests / Q000379:methods*; D012015:Reference Standards; D013045:Species Specificity; D013997:Time Factors