Validation studies of the spiral plating method to determine the potency of lactobacillus-containing probiotics

Scientific relevance. Viable cell counting is an important microbiological test for the quality assessment of medicinal products containing live microorganisms. To optimise labour and material costs and enhance testing precision and reproducibility, it is practical to use partially automated instrumental methods, such as the spiral plating method.

Aim. The aim was to conduct a validation study of the spiral plating method for assessing the potency of biologicals containing live bacterial cells, using a lactobacillus-containing probiotic medicinal product as a case study.

Materials and methods. This study used a culture of Lactiplantibacillus plantarum isolated from a probiotic medicinal product. Spiral plating on agar-based biological culture media was performed using an automatic Eddy Jet 2 plating system. The study used an IUL Flash & Go colony counter for automatic reporting of the results. The validation study was conducted according to the general chapter on the validation of microbiological testing methods (OFS.1.1.0021.18) of the State Pharmacopoeia of the Russian Federation.

Results. According to the validation results for the main parameters, the spiral plating method had the range of 10⁴–10⁵ CFU/mL; the limit of quantification of 10² CFU/mL; and the coefficient of linear determination, R², of 0.99. The accuracy of the spiral plating method in determining the potency of the test sample was 93%; the repeatability was 4.9%.

Conclusions. The study results confirm the similarity of the spiral plating method with an automatic colony counter to Koch’s plating method, which is currently used in accordance with the State Pharmacopoeia of the Russian Federation, in terms of the validated parameters. Therefore, spiral plating can be used to evaluate the potency of lactobacillus-containing probiotics. Spiral plating can help improve the cost-effectiveness and accuracy of testing.

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