316 J Clin Pathol 1998;51:316–323 Technical report J Clin Pathol: first published as 10.1136/jcp.51.4.316 on 1 April 1998. Downloaded from The Vitek analyser for routine bacterial identification and susceptibility testing: protocols, problems, and pitfalls N Shetty, G Hill, G L Ridgway Abstract covered, maintenance and quality control Automated and semiautomated technol- costs, and the presence of a versatile software ogy in microbiology has seen great ad- package. This report describes our experiences vances in recent years. The choice of with the Vitek system (bioMerieux, UK) in the automated equipment for the identifica- one year since its inception into a busy micro- tion and susceptibility testing of bacteria biology diagnostic laboratory in the United in a routine diagnostic laboratory depends Kingdom. It is worth noting that the choice on speed, accuracy, ease of use, and cost and range of antibiotics on susceptibility factors. The Vitek analyser (bioMerieux, testing cards were custom made for the UK) was installed in a busy diagnostic University College London Hospitals teaching hospital laboratory in London. (UCLH). This report describes one year’s experience. Changes to work practice as a result of incorporating the equipment into Identification and susceptibility testing the laboratory, and the advantages and on the Vitek system disadvantages of automation in key areas Identification of microorganisms is accom- are described in detail, together with pos- plished by biochemical methods. A turbido- sible solutions to problems. The Vitek metrically controlled suspension of pure colo- analyser was found to be valuable for the nies in saline is inoculated into identification http://jcp.bmj.com/ speed and accuracy with which results cards. These cards contain 29 diVerent bio- were available for the common bacterial chemical broths in reaction cells and one nega- pathogens. Results of susceptibility testing tive control cell to assess growth and viability of were standardised according to NCCLS the suspension. Conventional catalase, coagu- guidelines and used breakpoint MICs to lase, and oxidase tests (where appropriate) and ascertain susceptibility and resistance; the results of a Gram stain are required before they were an improvement on disc testing. inoculation of cards. Incubation times vary on September 26, 2021 by guest. Protected copyright. This equipment is not a reference facility from two to 15 hours depending on the growth for diYcult to identify organisms and rate of the organism. The Vitek programmed many manual techniques, including some computer determines whether each well is disc susceptibility testing, will have to be positive or negative by measuring light attenu- retained by the laboratory. ation with an optical scanner. When the (J Clin Pathol 1998;51:316–323) incubation period is completed, the reactions are analysed automatically and the identifica- Keywords: Vitek analyser; automation; bacterial identification and susceptibility testing tion is printed. Antimicrobial susceptibility tests are run similarly on cards which contain dilutions of Rapid and reliable identification of microor- antimicrobials to determine the breakpoint Department of Clinical ganisms is essential for the eVective manage- minimum inhibitory concentration (MIC) Microbiology, ment of infectious diseases. Early diagnosis and against the organisms. There are separate cards University College for Gram positive and Gram negative organ- London Hospitals, treatment is crucial, reducing both morbidity Grafton Way, London and mortality and the danger of spread of isms. The MIC cutoV values diVerentiating WC1E 6DB, UK infection. In a cost conscious environment, sensitive, moderate, and resistant status for an N Shetty specific, targeted management and early dis- organism against appropriate antimicrobials G Hill charge from hospital is highly desirable. During are programmed into the system and are based G L Ridgway the last decade many automated and semiauto- on the NCCLS, USA guidelines.1 A compari- Correspondence to: mated bacterial identification and susceptibil- son of these values with those published by the 2 Dr Nandini Shetty; email: ity systems have been launched. The choice of BSAC yielded many diVerences. A decision [email protected]. one system over another depends on the speed was made use the NCCLS guidelines because nthames.nhs.uk with which accurate identification and suscep- it was felt that these values reflected a Accepted for publication tibility results are made available to the stringently controlled, standardised, and 26 January 1998 clinician, ease of use, spectrum of organisms widely accepted set of guidelines. Vitek analyser for routine bacterial identification 317 Table 1 Vitek card use (February 1996 to January 1997) J Clin Pathol: first published as 10.1136/jcp.51.4.316 on 1 April 1998. Downloaded from Total use Projected use Card description (mainly on urine bench) (all specimen types) Modifications in card type and/or use Gram negative organisms + Identification (GNI) 4600 6840 No change in card number or type ordered for the next year + Susceptibility Routine-GNS-PW* 400 3220 Change in card type (new GNS-QL card) Urine-GNS-PX* 4340 5000 No changes Gram positive organisms + Identification (GPI) 600 7720 No changes + Susceptibility Streptococci 400 1140 Terminated further orders (GPS-AH)* Staphylococci (GPS-AI)* 400 7460 Changed to incorporate staphylococci and streptococci (new GPS-AM card)* *See table 2. Initiation of the Vitek system into the that results when validated are automatically laboratory and analysis of card use downloaded and available to user screens The Vitek system was initially used exclusively throughout the hospital, saving on the consider- for the identification and susceptibility testing able time spent in entering results. A new of Gram negative isolates from urine speci- pathology computer system for the whole Trust mens. In the period ranging from February is imminent at the UCLH and will be automati- 1996 to January 1997 the laboratory received cally interfaced with equipment such as the over 41 000 urine culture requests. The actual Vitek analyser. At present, results are entered and projected analysis of card usage in the manually. Accurate assessments of turnaround laboratory is illustrated in table 1. A review of times and savings related to labour can only be the system at the end of one year showed the made when the interface is finally in place. need for changes in card type. In our experience such a review and the flexibility to Identification protocols using the Vitek make major antimicrobial changes (table 2) system was crucial to the continued use of the system To minimise duplication of work and maximise in the laboratory. eYciency it was decided that each bench would One of the undisputed advantages of the be provided with flow diagrams for quick and Vitek, if loaded with cards early in the day, is easy reference. The following flow diagrams the speed with which it yields an identification illustrate the changes in microbiology practice and susceptibility test result on a Gram that were a direct result of the acquisition of the negative isolate, sometimes in less than four Vitek system (figs 1–6). hours. The system also obviates the need to There were a few minor problems. Possible http://jcp.bmj.com/ read API strips and disc diVusion plates the E coli 0157 was being identified in urine more next day, thus saving several hours. often than with conventional methods An ideal hospital computer system would be (because sorbitol is incorporated in the panel able to incorporate the Vitek laboratory compu- of biochemical tests used for identification). ter interfaced with the hospital mainframe, so Serological confirmation of these isolates Table 2 Custom made susceptibility test cards for UCLH use on September 26, 2021 by guest. Protected copyright. GPS-AH streptococcal isolates: only GNS-PW Routine coliforms from sources GNS-PX Gram negative isolates in the GPS -AI All staphylococcal isolates group B and enterococci from sources other than urine and all pseudomonads urine other than pseudomonads except those from urine other than urine Ampicillin Ampicillin Penicillin Penicillin Azlocillin Co-amoxiclav Oxacillin Ampicillin Piperacillin Cephalothin Erythromycin Erythromycin Imipenem Cefuroxime Fusidic acid Chloramphenicol Cefuroxime Nalidixic acid Tetracycline Tetracycline Ceftazidime Ciprofloxacin Trimethoprim Rifampicin Ciprofloxacin Gentamicin Gentamicin Gentamicin 500 Gentamicin Nitrofurantoin Amikacin Streptomycin 2000 (equivalent to Amikacin Tetracycline Teicoplanin high level gentamicin) Trimethoprim Trimethoprim Vancomycin Teicoplanin Extended spectrum B-lactamases B lactamase Vancomycin (ESBL) Changes in card types following Vitek audit of 1996–1997 New GNS-QL card No changes New GPS-AM card for all Further orders terminated Ampicillin relevant gram positive isolates Co-amoxiclav from urine and other specimens Piperacillin Penicillin Piptazobactam Oxacillin Imipenem Erythromycin Cefuroxime Gentamicin Ceftazidime Fusidic acid Ciprofloxacin Teicoplanin Gentamicin Vancomycin ESBL Trimethoprim Nitrofurantoin Tetracycline â-Lactamase 318 Shetty, Hill, Ridgway Significant colonies from a CLED plate J Clin Pathol: first published as 10.1136/jcp.51.4.316 on 1 April 1998. Downloaded from Gram negative organisms Gram positive organisms (processed by the Vitek) (partially processed by the Vitek) Gram stain and catalase mandatory Lactose Non-lactose Mucoid lactose Streptococci Staphylococci