Why is anaerobic incubation critical for lactic acid bacteria recovery?

Lactic acid bacteria are anaerobic microbes that generate energy through oxygen-independent metabolism; incubation without oxygen supports cellular reactivation and growth after cold stress.

How does optical density measurement at 610 nm indicate microbial recovery?

Increasing optical density at 610 nm reflects rising cell concentration during anaerobic incubation, serving as a quantitative proxy for viable cell growth and metabolic reactivation.

What role does streaking onto agar plates play in isolating active colonies?

Streaking dilutes the culture to separate individual cells, allowing only metabolically active bacteria to form visible colonies under anaerobic incubation, while damaged cells fail to grow.

Why is transfer to fresh broth necessary after initial recovery?

Transferring to fresh nutrient broth provides renewed resources for exponential cell division, enabling the culture to reach high density and physiological readiness for downstream use.

How does colony isolation contribute to obtaining a pure, high-performing culture?

Picking isolated colonies from agar plates selects for single, viable clones, eliminating contaminants and stressed cells, resulting in a genetically uniform and functionally robust working culture.

Revival and Growth of Lactic Acid Bacteria

JoVE Encyclopedia of Experiments

Microbiology

0 views • 3:24 min • September 26th, 2025

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Begin with a frozen glycerol stock of lactic acid bacteria, anaerobic microbes that grow without oxygen.

Freezing exposes the bacteria to cold-induced stress, reducing their cellular function.

Vortex the tube to resuspend the cells, and transfer an aliquot into a nutrient broth. Incubate under anaerobic conditions.

In this environment, the bacteria generate energy through anaerobic metabolism, which supports their recovery and restores cellular activity.

Transfer the culture to a fresh broth to provide renewed nutrients for rapid cell division.

Actively growing cells acidify the medium, indicating their recovery and growth.

Streak the culture onto agar plates. Incubate under anaerobic conditions to support bacterial growth.

Metabolically active cells form visible colonies, while damaged or inactive ones fail to grow.

Transfer the isolated colonies into a fresh broth, vortex, and incubate anaerobically to attain a pure, high-performing culture.

This method restores viable cells for downstream applications.

Take the prepared glycerol stock of lactic acid bacteria, or LAB strains, in two milliliters centrifuge tubes from the minus 80 degree Celsius ultralow freezer.

Do not allow them to thaw before use. Clean and disinfect the opening of the centrifuge tubes with 70% alcohol and gently vortex before use. Pipette about 250 microliters of the stock LAB culture from the centrifuge tubes to fresh two milliliter MRS test tubes.

Gently vortex the test tubes, parafilm them, and anaerobically incubate them overnight at 42 degrees Celsius for 12 to 16 hours. Next, take about 500 microliters from the overnight grown cultures from the two milliliter MRS test tubes to fresh seven milliliter MRS test tubes, vortex them, and anaerobically incubate them overnight at 42 degrees Celsius for 12 to 16 hours. Assess the microbial growth by measuring the optical density or growth of the cultures at 610 nanometers with a UV visible spectrophotometer and record acceptable results between 0.7 and 0.9.

Streak the overnight cultures from the seven milliliter MRS tubes onto MRS and MRCMPYR agar plates and incubate them anaerobically for 72 hours at 42 degrees Celsius. Pick the isolated colonies from the agar plates, transfer them into fresh seven milliliter MRS test tubes, gently vortex, and anaerobically incubate them overnight at 42 degrees Celsius for 12 to 16 hours. Store the agar plates containing the isolated strains at four degrees Celsius in the refrigerator for a week.

Next, measure and confirm the optical density from the seven milliliter MRS test tubes of the LAB cultures isolated from the streaked plates at 610 nanometers and use them as working cultures for all related experiments.