TSA Agar at the Heart of Culture Media Quality
Tryptone Soy Agar (TSA) is the reference medium used to assess the quality of most other culture media employed in microbiological analyses in food, pharmaceutical, cosmetics, and water sectors. Yet behind its apparently simple composition lies a major challenge: how can its performance be guaranteed over time and its quality monitored effectively?
This is the question that the Biokar Diagnostics team sought to address through a study aimed at defining a robust strategy for validating and monitoring TSA agar.
A Reference Medium at the Core of Standard Requirements
The ongoing revision of the NF EN ISO 11133 standard reinforces the central role of TSA agar as the reference medium for culture media quality control. This development also underscores the importance of using validation and monitoring methods that take the different sources of variability into account.
An Approach Based on Controlling Variability
To assess the performance of TSA agar, several microbial strains were inoculated onto validated agar batches and batches undergoing validation. The tests involved different technicians in order to incorporate handling-related variability.
The researchers then analyzed the results by calculating productivity ratios for each strain and each operator, while applying a statistical approach based on the analysis of overdispersion in microbiological counts.
This methodology was also supplemented by regular monitoring of commercial strains and strains produced in the laboratory in order to track changes in the medium’s performance over time.
Beyond the Productivity Ratio: A More Comprehensive View of Quality
The results show that analyzing overdispersion using a negative binomial distribution provides a more relevant assessment of the variations observed than conventional approaches based on logarithmic transformation.
Although all the productivity ratios obtained were above the regulatory threshold of 70%, demonstrating good nutritive performance, the authors consider that this threshold alone is not sufficient to fully qualify a culture medium. Indeed, accepting a minimum ratio of 70% amounts to tolerating a performance decline of up to 30% with each successive batch validation; if several strains remain at this lower limit over time, a gradual deterioration in the medium’s nutritional quality may occur without being detected early enough.
The value of the proposed approach lies in simultaneously taking into account the results from all tested strains and all technicians involved. This overall view makes it possible to define a target value close to 100%, providing a more faithful reflection of the culture medium’s actual quality.
Continuous Monitoring Through Control Charts
One of the key findings of this study is the value of control charts for continuously monitoring the quality of TSA agar.
By drawing on appropriate statistical indicators, these tools make it possible to monitor changes in quality and anticipate potential deviations when comparisons are made with other culture media.
Towards Better Control of Culture Media
This study confirms that validating and monitoring a reference medium such as TSA agar requires a comprehensive approach that integrates microbiological performance, experimental variability, and statistical monitoring tools.
By combining analyses of overdispersion in the raw results, productivity ratios, and control charts, it becomes possible to strengthen the robustness of quality-control protocols and anticipate potential deviations more effectively.
At Biokar Diagnostics, this approach fully reflects our commitment to providing high-performance, reliable culture media that meet the increasingly stringent requirements of microbiology laboratories.