Sampling of probiotic bacteria from food samples and isolation on specialised enriched media

Sampling of probiotic bacteria from food samples and isolation on specialised enriched media


Probiotics are defined as living microorganisms which resist gastric, bile, and pancreatic secretions, attach to epithelial cells and colonize the human intestine.

In recent times, there has been an increased interest to adapt healthy diets, which help in preventing diseases, and as a consequence, the study and development of new functional foods has gained much importance. Food additives as probiotics and prebiotics may exert positive effects on the composition of gut microbiota and are subject of intensive research. A daily consumption of high levels of probiotic bacteria is required to confer health benefits. Despite the importance of viability of these beneficial bacteria, studies conducted have shown poor viability of probiotic bacteria, especially Bifidobacterium, in functional foods. It would be interesting to study the changes in the number of viable probiotic bacteria during storage of functional foods more extensively.

The allergy to dairy products affects negatively some persons. At present, some non-dairy probiotic beverages are being commercialized. Probably, beverages such as fruit and vegetable juices would be the next food category where the healthy probiotic bacteria will make their mark.

Fruit juices may be an alternative vehicle for the incorporation of probiotics because they are rich in nutrients and do not contain starter cultures that compete for nutrients with probiotics. Fruit juices contain high amounts of sugars which could encourage probiotic growth and could easily be monitored using a refractometer. The food industry refers to foods supplemented with probiotics as ‘functional foods’.


  1. Food samples
  2. MRS media (agar)
  3. Petriplates
  4. Laminar air flow hood
  5. Distilled water
  6. Inoculating loop
  7. Spreader
  8. Ethanol (70%)
  9. Incubator


  1. Obtain the food samples and make serial dilutions of the samples.
  2. Spread 0.1ml of 10-1 the dilution on MRS plate and incubate at 37°C overnight. Leave it for 48 hrs if necessary.
  3. Record the number and types of colonies. Pick each type of colony and streak it onto fresh plates to obtain pure cultures.
  4. Incubate the plates at 37°C overnight.
  5. Note the colony morphology of each type and record your results.
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