Laboratories are under increasing pressure to reduce costs without reducing services. Many believe that large automated systems with proprietary plastic cards or panels are the most cost effective, but other systems exist that strongly challenge that assumption. For example, the digital camera and PC-based technology described here automate antibiotic disk susceptibility testing (AST) and provide organism identification (ID) using non-proprietary methods and materials recommended by the U.S. National Committee of Clinical Laboratory Standards (NCCLS) M2 A7, M39 and M35 (ID) documents.
The labor to setup NCCLS disk tests and the two widely used AST-ID automated systems is comparable. Disk test reading and interpretation time is also comparable. Most IDs can be accomplished in minutes and for a few cents. Speed and accuracy are comparable and the primary difference is in the capital equipment and daily materials costs. For example, the equipment and proprietary card/panel costs may run 600 to 1200 percent higher than the BioMic-IDTree System, depending on the number of cards/panels per isolate. The ability to change antibiotics to comply with cost-effective hospital formulary practices also is best accomplished with routine disk diffusion tests.
(top) IDTree follows U.S.A. NCCLS M35 and outlines minimal characteristics required to identify common organisms to genus and species with >= 95% accuracy.
(center) View the MIC scale over the continuous agar gradient by mouse clicking on a disk.
(bottom) The antibiotic test plate image appears in <1 second on the BioMic screen with zone diameters shown to review and edit.
The BioMic Vision
The new BioMic Vision System from Giles Scientific Inc., in Santa Barbara, Calif., automatically reads each NCCLS disk test and quality control plate in one second, including fastidious organisms on blood agar. This system has evolved since its first appearance with an electronic caliper 16 years ago. All test results are now automatically checked against the Expert system and QC rules and interpreted by NCCLS guidelines. Accurate MICs are determined from the continuous agar gradient around each disk. Epidemiology reports are generated in seconds, including the critical cumulative resistance summary reports following the new NCCLS M39 guidelines. These reports facilitate and guide initial therapy before test results are available.
An efficient AST-ID work flow and lower skill requirements are among the oft-cited reasons to automate with proprietary panel/card systems, but they offer less flexibility and a significant increase in cost per isolate, $6-12 over the NCCLS methods that are $1+ per isolate. Actual cost savings worksheets are available on the BioMic web site. The common proprietary card/panel systems provide about 95 percent accuracy, but 5+% of test endpoints must be considered as “blindly” acceptable errors; whereas microbiologists using BioMic can adjust any zone endpoint on screen with a mouse-click. The BioMic allows all plate-images to be saved for next-day review by a supervisor, or saved permanently. The combination of BioMic’s Expert-checks/messages also provides consistent and accurate results and ongoing training.
Rapid “same day” results are the claim of some AST-ID card/panel systems; but the fastest and least expensive means provides physicians with an almost immediate identification using rapid/spot tests outlined in the NCCLS M35 document.
The IDTree program and a cumulative antibiogram report can help guide initial therapy. Antibiotic disk test results can be read on rapid growers at five to seven hours and reported as preliminary with results comparable to AST card/panel systems. In contrast, direct disk/card/panel-based test results are usually unavailable when therapy is initiated.
Expert System
The Expert System in BioMic checks all tests against 2,358 predefined rules for improbable and unusual results and for tests not quality controlled or out-of-control within the previous seven days. Expert messages, tips and precautions are shown on-screen, for example: “Check identification & measurement.” NCCLS rules include, for example: “if Staphylococcus is resistant to oxacillin, report all cephalosporins and penicillins as resistant.” Difficult-to-detect beta-lactamase/ESBL resistance may be detected using a combination of disks as resistance markers. On-screen messages improve accuracy, reduce supervisory time, and provide ongoing training. Laboratories can select and define rules, add comments and suppress certain test results automatically.
The IDTree System
Organisms demonstrate unique biochemical and morphologic characteristics that provide a means to identify them to genus and or species and thus serve to guide antimicrobial treatment. Accurate and rapid identification may enable earlier therapy.
The IDTree flowcharts outline the minimal characteristics required to identify common bacteria and yeast to genus and or species with >= 95% accuracy. These charts generally do not involve the use of commercial products. This program is based on the NCCLS M35 document, expert microbiologists worldwide and textbooks. The rapid test procedures in these charts were designed to accurately identify most isolates from non-sterile body sites with equal or better accuracy than many commercial tests and systems. These identifications are intended to be reported directly, not as presumptive identifications, because the likelihood of correct identification is comparable (>95% accuracy) to conventional and automated methods.
Summary
The BioMic Vision — IDTree System is a cost-effective system for antibiotic testing and organism identification. It improves consistency and accuracy, provides MICs, rapid identification and flexibility. These systems, in use in 42 countries, require no maintenance. Disposable materials can be from any source and software updates with new drugs, antibiotic guidelines and ID flowcharts are available annually. In an era of increasing cost consciousness, this new computer software-based system can make a critical contribution to reducing hospital deficits.
David Gibbs is president and founder of Giles Scientific in Santa Barbara, Calif.
For more information about the BioMic Vision-IDTree System, Select Reader Service Number 260, go to their Web site (www.biomic.com) or call 805-963-3876/800-603-9290.
