# A vacuum lyophilization and bacterial tablet-based method for culture medium evaluation and potential use in probiotic products

## TL;DR

A new method using freeze-dried bacterial tablets is developed to evaluate culture media, offering a simpler and effective alternative to current standards.

## Contribution

A novel disposable bacterial tablet method is introduced for culture medium evaluation, showing high conformity with ISO standards.

## Key findings

- The GBSS recipe showed the highest survival rate for Escherichia coli during freeze-drying.
- The novel method demonstrated 94.1% sensitivity and 88.9% specificity compared to ISO 11133-2014.
- The freeze-dried bacterial tablet method is highly conforming to the ISO standard (χ2 = 0.25, p > 0.05; Kappa = 0.75).

## Abstract

The fundamental step in microbiological detection is the preparation of culture medium. The reliability and accuracy of microbiological assay heavily relies on this step. Currently in China, the most recognized standard method for such medium evaluation is ISO 11133-2014. However, this method requires highly complicated biosafety management, detailed standard strains record-keeping and substantial working time.

Bacterial tablet is considered to be a novel strategy for bacteria culture medium evaluation. The filter membrane as a carrier ensures uniform cell dispersion, forming a singular colony that can facilitate counting. We examined the viability and storage durability of vacuum freeze-dried bacterial tablets using a filter membrane as a carrier and utilized the results to evaluate culture medium. We found that the recipe GBSS (Glycerinum, Brain Heart Infusion, Sucrose, Sodium Glutamate) showed the highest survival rate for Escherichia coli in vacuum freeze-drying. As a qualified medium, the productivity of target bacterium should be greater than 0.7. A comparison of freeze-dried bacterial tablet method with ISO 11133-2014 quantitative method showed the sensitivity and specificity of this novel method were 94.1% and 88.9% respectively. The results suggested that vacuum freeze-dried bacterial tablet method had high conformity when compared to ISO 11133-2014 quantitative method (χ2 = 0.25, p > 0.05; Kappa = 0.75).

Hence, vacuum freeze-drying method is an integral part of preservation of bacterial strains and the preparation of related biological products. In conclusion, we have developed a novel and effective disposable product for estimating efficiency of the culture medium.