How Colony Counters Are Used In The Modern Laboratory

Colony counters are exactly as the name suggests - instruments which are used to

count bacteria and other microorganism colonies on a plate of agar or other culture medium. These instruments have progressed from the earliest designs, which were nothing more than a lighted surface; agar plates were set on top of the plate and colonies spotted and marked manually on the plate's outer surface with a felt tip pen. As you could imagine (or know all too well if you were working in a life sciences laboratory in the bad old days when the term colony counters really referred more to the laboratory personnel engaged in this time consuming task.

Culturing colonies of microorganisms to sizes where they become readily visible to the naked eye can take a significant amount of time, making the manual method of colony counting less than ideal, to understate the case. The manual method was not only slow, but inefficient and not always entirely accurate. In the best case scenario, a laboratory might have an automated plate reader - but this was still definitely a low throughput sort of system.

Newer generations of these devices are much more sophisticated. There are now electronic hand held colony counters which are capable of marking and counting colonies of bacteria and other microorganisms simultaneously.

Modern colony counting devices scan culture media to identify light and dark areas and counting the locations which are characterized by user definable criteria. Some of these newer models are designed to scan for specific types of colonies such as viral plaques or specific types of microbial colonies.

The higher sensitivity of these counters allows them to detect and count far smaller colonies, plaques and other formations than with the traditional lighted surface method. This is true even when the colonies are set against complex backgrounds with low contrast - it also means that the growth time for the colonies is greatly reduced.

Many newer colony counters also support multi-well plates, significantly improving the potential throughput of colony counting applications. Counters are also used to determine the density of microorganisms in liquid culture media. This is performed by using a sample of the culture (usually diluted) on a culture plate and incubating the samples until colonies have formedsince colonies will form where a single microorganism was located in the sample, this provides a method of estimating density in the original liquid medium.

Environments where counting colonies of microorganisms is an important part of workflow include not only medical facilities where colony counting is used to establish or confirm diagnosis but also in quality control and R&D laboratories for the food and pharmaceutical industries and of course, life sciences laboratories of all types. These colony counters use methods including LED-based illumination, high resolution optical scanning technologies and software which assists in the analysis of the results provided by the instrument.

The increased (and still increasing) sophistication of the instruments used to count colonies of microorganisms is a boon to laboratory personnel who no longer have to stoop over an agar plate with pen in hand - and whether were aware of it or not, all of us. We've all benefited from the medical and scientific advances made possible through faster, more accurate and reliable results that new, automated colony counters provide.

by:Andrew Long

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