Walk-away pipetting of serial dilutions for MIC testing

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Walk-away pipetting of serial dilutions for MIC testing

Antibiotic resistance is on the rise, with potentially disastrous consequences for our wellbeing and increased economic strain on our healthcare systems, creating an urgent need for novel antimicrobial compounds. Drug discovery research to identify new antibiotics requires large-scale screening of new or modified candidate drugs to evaluate their activity and potency. In this early phase of discovery, the main researchers are generally trying to identify one or more of the following criteria:

  • MIC – minimum inhibitory concentration, the lowest concentration of antimicrobial that inhibits the growth of a microorganism.
  • IC50 – half maximal inhibitory concentration, a measure of the potency of a compound in an inhibitory biological or biochemical functional assay.
  • EC50 – half maximal effective concentration, the concentration of a compound that induces a response halfway between baseline and maximum response.
  • LD50 – median lethal dose, the dose required to kill half the population in a test sample.

Determining these parameters requires multiple dilutions and several replicates of each candidate compound, necessitating precise pipetting and mixing to ensure robust and reproducible results. Determining the MIC is often the first step in this process, so we will focus on this example show you how automating your pipetting can increase the reproducibility and productivity of your workflows.

How is the MIC determined?

A common approach for MIC determination is to use a standard microtiter method – creating a two-fold serial dilution of the candidate compound in liquid growth medium in a microplate, then inoculating every well with a predefined amount of bacteria. The microplates can then be incubated and assessed for bacterial growth using a microplate reader to identify the lowest effective concentration of compound. This approach can be used to screen thousands of compounds, which is likely to be tedious, time consuming, and error and contamination prone if performed manually.

Antimicrobial susceptibility: Minimum inhibitory concentration (MIC) testing results in a 96 well plate

Simplifying serial dilutions

At INTEGRA, we are committed to finding easier solutions to routine and repetitive pipetting tasks like serial dilutions. Our high quality electronic multichannel pipettes and pipetting robots can solve many of the issues that come with manual pipetting, offering improved performance, precision and reproducibility to maximize productivity. For example, combining the ASSIST PLUS pipetting robot with a VOYAGER adjustable tip spacing pipette provides an elegant walk-away solution for performing serial dilutions of multiple samples in parallel.

This set-up can automate the transfer and mixing steps, performing them faster and more reliably than a technician working at the bench. Pipetting heights, speeds and mixing parameters are also consistent across all dilutions – ensuring reproducibility – while avoiding the ergonomic hazards of manual pipetting.

ASSIST PLUS pipetting robot

Crucially, the automated adjustable tip spacing function of the VOYAGER allows rapid transfer of compounds or inoculum from tube formats directly to microplates, eliminating the need for time-consuming single channel pipetting. This walk-away approach helps labs reach their full testing capacity and accelerate drug development workflows. Read here how the ASSIST PLUS is supporting scientist at Southmead Hospital in Bristol, UK, in their daily MIC testing workflows.

Get more samples processed faster

INTEGRA also offers a number of benchtop pipetting solutions allowing you to simultaneously fill every well of a 96 or 384 well plate. These options massively increase throughput for plate filling, and even allow serial dilutions to be performed by only loading a single row or column of tips. Whole plate pipetting also helps to eliminate time-associated variability for cell-based assays by allowing parallel inoculation of every well to accelerate assay set-up. Find out how Evotec in Lyon, France, has improved its sample throughput with the VIAFLO 96.

Example of the ASSIST PLUS pipetting samples from the INTEGRA microcentrifuge tube rack into a 96 well plate.

Maintaining sterility

The compact footprints of our automated pipetting systems make them ideal for use under a laminar flow hood. Combined with our unique GripTips – which are designed to be perfectly aligned and never leak or fall off – this set-up helps to reduce the risk of contamination, potentially helping to avoid hours of lost work.

Easy operation

INTEGRA electronic pipetting systems are controlled via a common touch wheel interface, making it easy to switch between devices. This intuitive set-up enables rapid navigation and operation, and offers predefined and customizable programs to set up and run MIC assays. Operators can simply input their desired volumes, labware formats, mixing parameters and controls to create a complete assay workflow that boosts overall lab productivity.

VIAFLO 96/384 performing a serial dilution