VITEK 2 IDENTIFICATION CARD AND OPERATION

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Each VITEK 2 identification card has several rows of wells comprising of 8 rows of 8 wells that is made up of 64 wells per card (8 wells X 8 wells = 64 wells). The wells of the identification card contain different dehydrated media required for different biochemical tests targeted at identifying via biochemical reactions different microbial strains. These individual biochemical tests are meant for the identification of Gram-negative bacteria, Gram-positive bacteria and fungi (yeast cells). A capillary tube (which sucks the suspension of bacteria to be identified and dispenses into all the wells) is fixed to each VITEK 2 identification card. Microbial (bacterial or fungal) growth is spurred by the hydration of the dehydrated media in the card with a suspension liquid (e.g. distilled water). The cards are incubated in the card reader / incubation chamber of the VITEK 2 compact system. The colour changes in all the wells are recorded automatically in the VITEK 2 compact system. The results of the colour changes go to a computer system that is attached to the VITEK 2 compact system. The computer system has an inbuilt updated database of different bacterial and fungal organisms as per their unique biochemical reactions.

The computer automatically compares the results with those available in its library for different bacteria and/or fungi, and finally gives the name of the bacteria with a definite probability. For identification of the organism, the given bacterium or fungal organism, grown as isolated colony on a culture media plate or as pure culture grown on a slant are taken; and a loopful of the bacteria is transferred aseptically into sterile saline solution in a test tube and a suspension of the organism is made. The suspension should contain a prescribed density of bacteria, as determined by a densitometer. The test tube is fixed to the cassette and a card is fixed near it, such that the tip of the suction capillary tube of the card remains deeply submerged in the suspension. The number of test tubes and cards fixed to each of the cassette can be increased depending on the number of bacteria or fungi to be identified by the VITEK 2 identification cards. The cassette is put in the vacuum chamber of the system as shown in Figure 1 & 2.

A high vacuum is created inside the chamber, which forces the bacteria suspension to be sucked into the capillary tubes and dispensed into the wells of the cards. The cassette is taken out and put inside the incubation and analysis chamber where the capillary tubes are cut and the cut ends sealed automatically. The incubation process is allowed to run at a prescribed temperature for a prescribed period of time, which is programmed by the control panel on the VITEK 2 compact system. During incubation, which is usually in every 15 minutes, each VITEK 2 identification card automatically goes to the colour reader, which reads the colour changes in the wells and records them. The recorded results go to the computer, which automatically compares them with those, available in its library for different bacteria. Finally, it gives the names of the bacteria with definite probabilities. The used cards fall into the waste disposal chamber (waste collection bin) of the system for removal and final disposal after sterilization.

Figure 1: The VITEK 2 automated compact equipment and workstation for bacterial identification and antimicrobial susceptibility test (AST). VITEK 2 automated system is used for microbial identification (bacteria and yeast), AST and it can also be used for epidemiological studies especially in the typing of bacterial strains. (1). Barcode scanning system for data entry (2). Windows-based user-friendly computer (3). The VITEK 2 processing unit. Photo courtesy: BioMérieux.

FEATURES OF THE VITEK 2 AUTOMATED COMPACT SYSTEM FOR BACTERIAL IDENTIFICATION AND ANTIMICROBIAL SUSCEPTIBILITY  TEST (AST)

Helping the physician select the best treatment at a much faster pace based on the right microbial identification and antimicrobial susceptibility test is crucial in any infectious disease management and patient total wellbeing. Clinical microbiology laboratories are the first lines of defense for the detection of antibiotic resistance from clinical pathogens and/or samples. The current best approach for managing today’s problems of emerging infectious diseases and antimicrobial resistance to some commonly used and available antimicrobials is hinged on maintaining high-quality clinical microbiology laboratories in our hospitals. This will help provide good patient care outcomes through accurate and prompt identification of bacterial pathogens. The clinical microbiology laboratories should also carry out accurate and prompt antimicrobial susceptibility test (AST) on clinical pathogens – as a panacea to guide physicians on the right choice of antimicrobial therapy for each patient. Services provided by the clinical microbiology laboratories should be carried out in a prompt, accurate and rapid manner since results from such sections of the hospital are critical to the optimal care of the patient.

The VITEK 2 automated compact system has everything that the clinical microbiology laboratory needs for fast and accurate microbial identification, and for the performance of a fast and accurate antimicrobial susceptibility testing (AST). VITEK 2 automated compact system is a fully automated high-throughput system that performs bacterial identification by biochemical analysis using colorimetry. This high-throughput technique for bacterial identification and AST mainly focuses on the clinical microbiology laboratory especially in the area of providing increased levels of automation and increased capacity for higher volume laboratories. The VITEK 2 automated compact system is suitable for both small and large laboratories since it does not occupy much space.

A colorimeter is a device used to test the concentration of a solution by measuring its absorbance of a specific wavelength of light while colorimetry is the technology that is used to quantify and describe physically the human perception of colour. Colorimetric equipment that work on the principle of colorimetry such as the VITEK 2 automated compact system is similar to that used in spectrophotometry (which is a method used to measure how much a chemical substance absorbs light by measuring the intensity of light as a beam of light passes through a sample solution). The basic principle of the spectrophotometer is that each compound absorbs or transmits light over a certain range of wavelength. The advanced colorimetry of the VITEK 2 automated compact system provides high discrimination between microbial species – making microbial identification rapid and accurate. The VITEK 2 automated compact system for bacterial identification and AST also offers advanced colorimetric technology that allows for the identification of about 98 % of clinical pathogens from clinically-relevant samples.

NOTABLE FEATURES OF THE VITEK 2 COMPACT AUTOMATED SYSTEM

Some of the notable features of the VITEK 2 compact automated system are as follows:

  • The VITEK 2 automated compact system has a comprehensive updatable database of microbial strains; new generation of identification test cards. It makes use of a Windows-based user-friendly software and computer system for easy processing of test results.
  • The knowledge base of the VITEK 2 automated compact system is developed from about 100,000 references of microbial strains.
  • The system described over 2000 microbial phenotypes.
  • It has over 20,000 minimum inhibitory concentration (MIC) distributions for a variety of antimicrobial agents or antibiotics.
  • The VITEK 2 automated compact system can detect over 100 resistance mechanisms in microbial pathogens.
  • It provides a resulting range of five to seven MIC doubling dilutions per antibiotic on the average.
  • It has an extended MIC range to enable low-level resistance detection.
  • It deduces antibiotic results to meet formulary requirements in terms of prescribing the correct antimicrobial therapy.
  • It is fast, rapid and accurate; and it checks every result every time.

The VITEK 2 automated compact system provides accurate “fingerprint” recognition of bacterial resistance mechanisms and phenotypes as well as prompt and accurate AST results. The components of the VITEK 2 compact automated system for microbial identification and AST include: the reader/incubator, waste collection bin, cassette load/unload station, fill door, front user access door, top user access door, filler station, loading/load door and waste collection door (Figure 2).

Figure 2: Components of the VITEK 2 automated system for microbial identification and AST. 1. Fill door. 2. Front user access door. 3. Top user access door. 4. Cassette load door. 5. Waste collection door. 6. Cassette load/unload station. 7. Waste collection bin. 8. Reader / Incubator. 9. Control panel. Photo courtesy: BioMérieux.

BENEFITS OF THE VITEK 2 AUTOMATED COMPACT SYSTEM

  • It enhances workflow in clinical microbiology laboratory because of the short time it takes in processing clinical samples and/or isolates.
  • It enables rapid reporting of laboratory test results and reduces hands-on time which usually causes delay in cultural techniques of microbial identification and AST.
  • It reduces time to microbial (yeast and bacteria) identification.
  • It reduces time for obtaining antibiotic susceptibility testing results.
  • It offers an extensive identification and susceptibility menu.
  • It reduces waste with a miniaturized card-format that measures 10 cm x 6 cm x 0.5 cm and weighs only 16 grams (Figure 3).
  • The VITEK 2 automated compact system is compartmentalized; and thus it meet the needs of any size laboratory including small and large laboratories.
Figure 3: VITEK 2 colorimetric identification card. The VITEK 2 card is a bacteriological identification plate that enables the identification of a bacterium in clinical samples such as blood, urine and saliva and the execution of antimicrobial susceptibility test on pathogens by an automated high-throughput technique. The VITEK 2 system uses disposable cards known as the VITEK identification cards; and one card is required for the identification of one bacterium. The system can accommodate a series of cards (ranging from 20 cards upwards), which can be arranged on a cassette, thus enabling the identification of several bacteria at a time. Photo courtesy: BioMérieux.

Figure 3: VITEK 2 colorimetric identification card. The VITEK 2 card is a bacteriological identification plate that enables the identification of a bacterium in clinical samples such as blood, urine and saliva and the execution of antimicrobial susceptibility test on pathogens by an automated high-throughput technique. The VITEK 2 system uses disposable cards known as the VITEK identification cards; and one card is required for the identification of one bacterium. The system can accommodate a series of cards (ranging from 20 cards upwards), which can be arranged on a cassette, thus enabling the identification of several bacteria at a time. Photo courtesy: BioMérieux.

FURTHER READING

Ashutosh Kar (2008). Pharmaceutical Microbiology, 1st edition. New Age International Publishers: New Delhi, India. 

Block S.S (2001). Disinfection, sterilization and preservation. 5th edition. Lippincott Williams & Wilkins, Philadelphia and London.

Courvalin P, Leclercq R and Rice L.B (2010). Antibiogram. ESKA Publishing, ASM Press, Canada.

Denyer S.P., Hodges N.A and Gorman S.P (2004). Hugo & Russell’s Pharmaceutical Microbiology. 7th ed. Blackwell Publishing Company, USA. Pp.152-172.

Ejikeugwu Chika, Iroha Ifeanyichukwu, Adikwu Michael and Esimone Charles (2013). Susceptibility and Detection of Extended Spectrum β-Lactamase Enzymes from Otitis Media Pathogens. American Journal of Infectious Diseases. 9(1):24-29.

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