Introduction
Microbiology laboratories now play a crucial role in the rapid and accurate identification of species responsible for disease pathogenesis as a result of the advent of Multi-Drug Resistant Organisms (Guo, Ye, Zhao, Ma, Yang, & Luo, 2014).The VITEK 2 System
The VITEK 2 system is an automated microbiological tool for identifying clinically important microorganisms including bacteria and yeast and determining their susceptibility to antibiotics (Turnidge, 2015). It aids in identifying antibiotic resistance and the mechanism underlying it. In order to follow changes in the patterns of microbial resistance, epidemiologic trends and antibiotic susceptibility tests (AST) are essential for tracking, particularly in healthcare settings (Turnidge, 2015). For biochemical analysis, the method makes use of growth-based technology and cutting-edge colorimetry. It employs a calorimetric The technique utilizes growth based technology and cutting-edge colorimetry for biochemical analysis. It uses calorimetric reagent cards that are interpreted automatically after preparation, standardization, and incubation of a primary inoculum (Turnidge, 2015).The Process
In the VITEK 2, after isolation of the primary organism, an organism suspension is prepared from a standardized inoculum (Turnidge, 2015). The suspension is made from swabbing sufficient colonies obtained from a pure culture and suspending the organism in 3 milliliters of sterile saline. The inoculum is placed into the cassette where virtual linkage of the susceptibility card and the sample occurs. Each card has 64 wells with each well containing the representative antibiotic (Turnidge, 2015). Once the cassette is loaded, the machine manages the incubation and reading of each card automatically. The system allows for kinetic analysis where the wells are read by the optical system every 15 minutes (Turnidge, 2015). Growth changes for each well are also detected using photometric technology. VITEK 2 is mostly used in clinical microbiology laboratory where it offers increased automation (Prod'hom, & Greub, 2013).Results and Interpretation
Results are sent from the VITEK 2 machine to the workstation as soon as the test is completed. Obtained results of the isolates are viewed from the main screen. The results can be displayed in four categories: isolate, tech, bench or patient level (Guo et al., 2014). Bench and patient levels appear if the machine is configured for clinical uses. Calculations are done on raw data, and a comparison made to thresholds to determine test reactions (Guo et al., 2014). Quantitative values are obtained from the experimental results of the unknown organism after comparison to existing data in the database to determine proximity with the taxa in the database. If the data is not sufficiently unique or close to the database taxa, the strain is considered out of the scope of the database or a list of possible organisms given (Guo et al., 2014). Observed reactions of the organism are compared to typical reactions to come up with statistical probability. Identification confidence levels are graded on terms such as excellent, good, low discrimination, unidentified, etc. Offline supplemental testing may be needed when there is low discrimination, and the reactions are unable to discriminate between two or three organisms (Guo et al., 2014). The Advanced Expert System automatically validates the results of the susceptibility test by comparing the test result's minimum inhibitory concentration with known results in the database (Guo et al., 2014). The machine has different VITEK 2 ID cards that can identify a wide variety of organisms. For example, in a study of 560 common and rare gram-negative bacilli species, the VITEK 2 GN card correctly identified 96.7% of the isolates, and a 6.3% low discrimination (Prod'hom et al., 2013). Misidentifications accounted for 2.8%, and the unidentified organisms accounted for 0.2% (Prod'hom et al., 2013).Advantages and Disadvantages
The VITEK 2 instrument has several advantages. Its high automation allows for optimized workflow (Guo et al., 2014). The staff is freed as it has full control of the process enabling them to perform other tasks hence increasing efficiency. It offers rapid microbial identification within a short time (Guo et al., 2014). Prompt species identification has the advantage of accurate diagnosis which results in effective treatment. It uses a user-friendly software which is easy to master. The intuitive software also means that technicians require less time for training which increases productivity (Guo et al., 2014). The VITEK 2 ID cards have pre-applied barcodes which enhances traceability besides the cards minimizing the risks for transcription errors (Turnidge, 2015). The advanced colorimetric substrates in the cards have an advantage of higher accuracy. Compared to microtitre methods, VITEK 2 instruments and consumables have less disposable wastes (Guo et al., 2014). However, in a study by Prod'hom et al. (2013), VITEK 2 had the disadvantage of low sensitivity in detecting some drug-resistant subpopulations of Enterobacter cloacae. The cards must also be stored in the refrigerator which may be inconvenient. Its results can be difficult to interpret resulting in errors during result interpretation (Guo et al., 2014). Analysis by an Expert must be performed before finalization and printing of the results which may prove inconvenient to technologists. Replacement of the saline and tips every month may be expensive besides the monthly maintenance of the machine being labor intensive. There is a risk of contamination to the saline pump dispensers (Guo et al., 2014).Conclusion
In conclusion, the VITEK 2 is a rapid and an easy to use method for microbial identification and testing for antimicrobial susceptibility. Despite the few cons, it has highly accurate results. With its state of the art software and hardware components, it offers an advanced technological platform for microbiological analysis.References
Guo, L., Ye, L., Zhao, Q., Ma, Y., Yang, J., & Luo, Y. (2014). Comparative study of MALDI-TOF MS and VITEK 2 in bacteria identification. Journal of thoracic disease, 6(5), 534-538.
Prod’hom, G., Durussel, C., & Greub, G. (2013). A simple blood-culture bacterial pellet preparation for faster accurate direct bacterial identification and antibiotic susceptibility testing with the VITEK 2 system. Journal of medical microbiology, 62(5), 773-777.
Turnidge, J. D. (2015). Susceptibility test methods: general considerations. In Manual of Clinical Microbiology, Eleventh Edition (pp. 1246-1252). American Society of Microbiology.
