Selecting a Rapid Microbiological Test

Looking at plate count methods for microbial enumeration, it can be seen how manual processes provide a breeding ground for errors. Food samples are weighed and then initially diluted in a specified liquid medium. The weighing and measuring is an error source.

The next step for many plate-counting methods is the serial dilution of the sample in order to provide plate readability. This might require four or more successive dilutions where measuring and pipetting errors can creep in. Most accredited techniques require the testing of replicate samples, adding to the amount of sample material and hardware, all of which has to be properly disposed of.

Common Sources of Error

One of the most common sources of error in the microbiology lab is the incorrect pipetting of small volumes of liquid. Once the serial dilutions are prepared, each one might be plated due to a lack of confidence that one of them is the accurate count. Even with the general acceptance of agar plate alternative technologies, the act of preparing and applying the sample to many plates is prone to error.

Of course, the microbes don’t comply with our need to see repeatable and clearly defined data. Colony counting is beset by subjectivity. Microbial colonies can vary in size and shape. They can swarm and spread. Some parts of the plated sample are unwanted artifacts that look like colonies. Plates might be contaminated from surrounding environment. This leads to one of the highest possibilities of error—plate counting itself. Once again, technology tries to rescue the situation with camera-based counters to remove the human element. So, it can be seen from the example of microbial plate counting that reducing steps is advantageous. Also, the right level of automation and correct choice of sampling equipment helps reduce errors.

Ergonomics

An often-unrecognized effect of manual methods in the QC lab is the physiological effect on the technician. Repetitive motion disorders are a real concern for companies who have invested time and effort in the training of skilled technicians. It seems to make sense that by reducing manual steps and the number and frequency of replicates, the physiological burden from staff members will also be relieved.

Choices of rapid methods in the dairy industry offer some insight into how the food companies’ investment in skilled human resources can be supported and rewarded. By choosing a total plate count, or TPC, method that uses only the raw milk as a sample, the need for dilution media is removed. This in itself saves time in preparing media and storing it. Then the probability of error in pipetting and delivering the media is negated as well.

By choosing a technology with high sensitivity and dynamic range, the need for serial dilution is eliminated. By adopting a technology where the sample size is relatively large and the quantitative outcome is not adversely affected by errors in sample size, a more reproducible result is gained. The technician’s job is more easily replicated with fewer repetitive motions.

Opportunity Costs

Buried in the justification for purchasing a new rapid test method is the opportunity cost. Trained technicians should be applied to the most challenging QC tasks that their training will support.

Not all test methods are created equal in terms of complexity of preparation or analysis. An evaluation of what tasks can be automated or outsourced will maximize the technician’s productivity. Test workload continues to expand, driven by regulation and customer desire for safer food and more detailed evaluation of possible spoilage or health drivers.

With test volume increasing, the right degree of automation along with good data generation can assist in guiding critical tasks toward the best-equipped people.

Summary

Data generation speed is only part of the story when selecting an alternate or replacement test method. By considering the workflow and effect on the lab environment, food companies can save costs and increase productivity. By considering the number and complexity of tests and QC steps, the skills and wellbeing of the staff can be protected, producing a healthy and productive workforce.