Abstract

Rapid Bacterial Count, Viability, and Gram Typing on Microcapillary Flow Cytometry

Stephanie Brunelle, Senior Product Manager, Cytek BioSciences

Evaluation of bacterial concentrations, viability, and Gram typing are frequently needed measurements in microbiological research. Characterization of bacteria has remained complex, cumbersome and labor-intensive with dependence on long culture times when using traditional colony counting plate-based methods and with limitations on daily throughput. Here, we present results from two quick and robust methods for bacterial analysis using combinations of microcapillary flow cytometry and dedicated kits based on pre-blended fluorescent dyes for count and viability determination and for Gram typing.  The kits are mix-and-read, enabling easy assay preparation steps. Samples are analyzed on the easy to use Cytek® Guava® easyCyte™ Systems which provide absolute counts of population, percent viability and fluorescence measurements. Assays include high precision Guava Bacterial Count & Viability kits that provide concentration and viability information simultaneously, and easy to interpret Bacterial Gram Typing kits that provide information on gram type of bacteria. The data demonstrate the performance of these assays on a range of bacterial strains. For bacterial Gram typing, our assay was applied to 10 different strains including Gram-positive and Gram-negative strains and showed results corresponding well with crystal violet staining.   Results could also provide information on whether individual or mixed strain types were present in the sample.  The analysis can be performed in tubes or plates. Our approach in evaluating concentration and viability allowed for the determination of dead and viable bacteria in samples in mixed culture or monoculture.  Approaches were applied to 10 different strains including both Gram-negative and Gram-positive strains. High precision was observed in both concentration and viability determination with average %CV of <12%. The combination of microcapillary cytometry and dedicated kits gives bacterial researchers new robust analytical tools for easy and rapid quantification and characterization of bacteria with reduced process times.