Today, most commercialized technology to directly detect bacteria requires complicated chemistry and/or advanced optics. SBT Instruments offers a new affordable approach, where bacteria are measured with no sample pretreatment, no incubation time, and no advanced user interaction. This is accomplished by using an electrically based measuring technology referred to as impedance flow cytometry. The electrical detection principle revolves around measuring the impedance in a small microfluidic flow cell, which enables us to detect bacteria immediately.

Working Principle

The concept of impedance flow cytometry in industry usage is novel. The concept is best explained by dividing it up in its three main components; cytometry, flow, and impedance. Cytometry is the science of measuring characteristics of cells including bacteria cells. Flow cytometry is the science of measuring characteristics of cells in a flow. Impedance flow cytometry involves measuring the characteristics of cells in a flow using impedance measurements. Most are familiar with the concept of electrical resistance, and impedance can be described as a more complex form of electrical resistance.

The working principle in SBT Instruments' product range involves circulating an aqueous solution through a microfluidic flow cell that has integrated electrodes. Bacteria, and other particles, transition across the electrodes, which results in a change in impedance between the electrodes. The impedance change for bacteria is uniquely different compared to other non-organic particles, and it is therefore possible to provide an almost immediate estimate of the bacteria and particle count in the sample. The working principle detects all bacteria species in the sample, as every bacteria will result in an impedance change when they enter the system. The unit of measurement is therefore total bacteria count per milliliter (bacteria/ml).

What is total bacteria count?

The technology directly identifies bactera on a single cell basis based on their electrical properties. This makes it the perfect tool for quantitatively assessing the bacteria count in a sample. We do not operate in secondary units such as relative light units or enzymatic reaction times, which may differ from measurement to measurement and from system to system. Instead we operate in actual bacterial counts that can not be misinterpreted.


Total bacteria count vs. total plate count

Total plate counts (TPC) has been the standard method for measuring bacteria for hundreds of years, but it has certain flaws. Most notably, the response time is notoriously slow, typically 24–72h. Additionally, only a fraction of the bacteria is actually counted during a TPC because different bacteria species grow better at different temperatures, at different ambient conditions, and on different nutritional media. The typical unit used for TPC counts is CFU, short for colony forming unit, which indicates how many bacteria formed colonies on the specific plate and at the specific combination of temperature/atmosphere/media. There is an effect typically referred to as the great plate count anomaly, which states that the actual number of bacteria in an environmental sample is usually 100x-1000x larger than what the total plate count suggests. If all bacteria are measured in a sample, independent of their preferred growth conditions, the bacteria count will typically be orders of magnitude higher than a corresponding CFU count and therefore also provide a much more accurate view of the bacterial content of the sample.