VITEK 2 Compact System: Introduction, Testing Requirements, Testing Procedure, Result Interpretation, and Keynotes

Introduction

The VITEK 2 compact system is an automated microbiology bacterial and fungal (mainly yeasts) identification and antimicrobial susceptibility system.

Testing Requirements

1. Culture plate of test organisms
2. Organims Categorozation for GP/GN/Yeast/BCL
3. Saline and saline dispenser
4. Test-tube
5. Vitek Tube Rack/ Vitek Tube Compact Cassette
6. Inoculating loop
7. Bunsen burner
8. Biosafety cabinet (BSC)
9. Densitometer ( DensiCHECK plus provided by the company)
10. Vortex
11. Micropipette and tips
12. Reagent Card- It is of following types-

• GN-Gram negative fermenting and non-fermenting bacilli
• GP-Gram positive cocci and non-spore-forming bacilli
• BCL-Gram positive spore forming bacilli
• YST-Yeasts and yeast-like organisms

11. AST-Card-It is also of the following types-

• Gram positive antimicrobial susceptibility testing (AST)Cards
• Gram negative antimicrobial susceptibility testing (AST) Cards
• Yeast antimicrobial susceptibility testing (AST) CARD

12. VITEK 2 Compact (machine)

Testing Procedure

• Categorize the isolated colony of organisms according to the reagent cards i.e. GN or GP or YST or BCL.
• Take two test tubes for one organism and place into the rack. Label the tubes with Identification number.
• Add saline provided by the company in both tubes up to 3 ml in each with provided dispenser.
• Prepare inoculum adding isolated colony by the help of inoculating loop and mix the tube using vortex mixer.
• Finally measure the optical density of the inoculum and it should be 0.5-0.063 for bacteria while for yeasts 1.8 to 2.2.
• Take 145 micrometer for Gram negative while 180 for Gram positive and yeast inoculum from first tube and place into second tube and finally mix the second tube for AST.
• After completion of above steps, place reagent card and AST card first and second tubes receptively.
• Loaded cards in Vitek Tube Compact Cassette is now ready for feeding in machine (VITEK 2 Compact).
• Place the cassette in the filler module.
• After filling the cards,transfer the cassettes to the reader oe incubator module.
• All the remaining steps are handled ny the instrument.
• Wait for 5-7 hours for report.

Result Interpretation

Organisms Identification

GN-Reagent Card: In this panel will show Gram-negative bacteria. e.g. Escherichia coli (99 %) or Klebsiella pneumoniae (96%) or Proteus mirabilis (98%) and so on

GP -Reagnent Card: In this group will display Gram-positive cocci and non-spore-forming bacilli. e.g. Staphylococcus aureus (99%), Enterococcus faecalis (98%), Streptococcus pyogenes (96%), Streptococcus agalactiae (95%), Streptococcus pneumoniae (99%), etc

YST- Reagent Card: It will exhibit Yeast and yeast-like organisms. e.g. Candida albicans (99%), Candida krusei (97%), Cryptococcus neoformans (99%), etc

BCL- Reagent Card will present Gram positive spore forming bacilli. e.g. Bacillus cereus (95%), Clostridium difficile (98%), Clostridium perfringens (97%), Clostridium tetani (94%), etc

Antibiogram of Organisms

In this panel minimum inhibitory concentration (MIC) of antibiotics according to isolate and the situation of the organism towards the antimicrobial agents whether susceptible, intermediate, or resistant will be displayed.

Keynotes

• Optimal concentration of organism is always preferred to give actual MIC of antibiotics.
• Never use expired reagent and AST card.
• Always use pure isolated colonies of test oragnism to omit inconsistent result.
• The VITEK 2 compact system should be in uninterruptible power supply (UPS).
• It is a rapid technique for isolation and identifation even antimicrobial susceptibility tests (AST) of test organisms.
• It is slightly costly method than conventional techniqe.

Further Readings

• https://www.biomerieux-diagnostics.com/vitekr-2-compact-0
• https://www.biomerieux-usa.com/vitek-2
• https://www.ncbi.nlm.nih.gov/pmc/articles/PMC130656/
• https://www.gundersenhealth.org/app/files/public/6557/Lab-Policies-Vitek-2-Compact—Identification-and-Susceptibility-Testing-Lab-1512.pdf