How to Automatize the Preparation of Microbial Suspensions for Antimicrobial Susceptibility Testing AST

Background:
Automated Antimicrobial Susceptibility Systems provide reliable results improving clinical outcomes although the microbial suspension preparation is still completely manual. Colibrí® is a new automated system able to pick colonies from plates, re-suspend them in saline solution, check the turbidity of the suspension with the on-board nephelometer and adjust it if required.
Objective:
The aim of the study was to compare manual microbial suspensions preparation for Antimicrobial Susceptibility Testing (AST) to Colibrí® automated preparation.
Colibrí® is able to:
– Pick colonies using disposable tips (1)
– Release bacteria colonies in a saline solution tube (2)
– Check the microbial suspension turbidity using the on-board nephelometer (3)
– Adjust the microbial suspension adding colonies or saline to obtain a 0.5 MacFarland
– Prepare the microbial dilution needed for processing with AST system
– Prepare the purity plate from the microbial suspension (4)

Results
The results were interpreted with Biomerieux Expert System EUCAST 2015:

– 318 antibiotic combinations were tested for Gram positive: 1 minor error (0.31%) and 1 major error (0.31%) were found.
– 306 antibiotic combinations were tested for Gram negative: 9 minor error (2.94%) and 1 very major error (0.32%) were found.
– Only 1 discrepant result could be related to the viable count where the manual preparation was 5-fold higher than Colibrí ® microbial preparation.
Five out of the 44 strains tested were defined as MDR organisms
according to Magiorakos et al 2011 (1).

Conclusions:
The data generated in this study demonstrate Copan Colibrí®:
– is able to automatically prepare microbial suspensions from different bacteria colonies directly from agar plate culture.
– provides comparable results to those obtained with manual preparation
– standardizes the preparation of microbial suspensions for AST and purity plates eliminating the person to person variability.
– Reduce the exposure to pathogens improving staff safety

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Colibrí™ Universal Colony Picker