Application of Control Charts in Quality Characteristics Evaluation of Microbiological Media

Abstract

Microbiological culture media are the backbone of any microbiology laboratory. However, appropriate monitoring of their quality characteristics is crucial to ensure accuracy and validity of the results derived from them. The microbiologist should be aware and well-focused on these quality attributes and not only the activities performed with them. Consistent and controlled shipment, storage, handling and preparation conditions and methods are critical for reproducible performance of the media. The application of Shewhart charts to trend the quality attributes of culture media batches provides internal monitoring for important characteristics of these media in a microbiology laboratory. Two approaches can be used, variable or attribute
control charts. Both can be customized according to the nature of laboratory activity in terms of number and frequency of the prepared and tested-culture media. Variable control charts can be used for a limited number of measurable properties of media such as thickness of the solid media, gel strength and pH, while attribute charts are suitable for monitoring of defects for microbiological culture media. Some of the quality
characteristics may have certain specification limit (SL) values such as growth promotion (GP) failure rate, the depth of the agar medium in the culture plate, gel strength, contaminated fraction from total batch and pH. Thus, the statistical process control (SPC) may be useful in the assessment, control, investigation-on-failure and prediction of the performance of microbiological culture media. Shewhart control charts provide the microbiologist with a tool for quality monitoring and improvement of the prepared culture media.