Background: Escherichia coli is a widely studied prokaryotic system. A recent study had demonstrated that reduced growth of E. coli after extended culture in Luria-Bertani broth is a result of depletion of fermentable sugars but able to sustain extended cell culture due to the presence of amino acids, which can be utilized as a carbon source. However, this had not been demonstrated in other media. The study aimed to determine the growth and viability of E. coli ATCC 8739 in 3 different media, Nutrient Broth (NB), Brain Heart Infusion (BHI) and Luria-Bertani Broth (LB) over 11 weeks.

Methods: Growth of E. coli ATCC 8739 was determined by optical density. Viability was determined by serial dilution/spread-plate enumeration. After 11 weeks, the media were exhausted by repeated culture. Glucose was added to the exhausted media to determine whether glucose is the growth-limiting factor.

Results: Our results showed that cell density in all 3 media increased to about 1 x 109 cells/ml by the end of week 1, from the inoculation density of 2.67 x 105 cells/ml, peaked at about 1 x 1013 cells/ml at week 4, before declining to about 5 x 107 cells/ml at week 7. Cell density is highly correlated to genomic DNA content (r2 = 0.93) but poorly correlated to optical density (r2< 0.2). Our results also showed that the spent media were able to support further growth after glucose-supplementation.

Conclusion: NB, LB and BHI are able to support extended periods of culture and glucose depletion is the likely reason for declining cell growth.

Key words: Escherichia coli (E. coli), Extended culture, Genomic DNA content, Glucose  
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