A new protectant medium preserving bacterial viability after freeze drying

Area of Science:

• Microbiology
• Biotechnology
• Food Science

Background:

• Freeze-drying is a common method for preserving microorganisms.
• Protective agents are crucial for enhancing bacterial survival and stability during freeze-drying.
• Gut bacteria require effective preservation methods for research and therapeutic applications.

Purpose of the Study:

• To evaluate a novel protectant medium containing sucrose, trehalose, skimmed milk, and antioxidants for preserving gut bacteria via freeze-drying.
• To assess the impact of this medium on the viability and morphology of Escherichia coli and Akkermansia muciniphila.
• To compare the efficacy of the protectant medium against a standard saline solution.

Main Methods:

• Freeze-drying of Escherichia coli and Akkermansia muciniphila with and without the protectant medium.
• Assessment of bacterial viability using plating techniques and flow cytometry.
• Evaluation of bacterial morphology via scanning electron microscopy.
• Testing on five human fecal samples.

Main Results:

• The protectant medium significantly increased bacterial survival rates (85-93%) compared to saline (0.36-37.50%).
• High viability was maintained in fecal samples (89.47% ± 7.63% by flow cytometry, 84.01% ± 7.44% by plating).
• Bacterial morphology (size and shape) was preserved in the protectant medium, unlike in saline.

Conclusions:

• The novel protectant medium effectively enhances the freeze-drying survival and stability of gut bacteria.
• This formulation preserves bacterial morphology, crucial for maintaining cellular integrity.
• The study uniquely combines morphological analysis with culture-dependent and independent methods to validate the protectant medium's efficacy.