Gradual and Step-wise Halophilization Enables Escherichia coli ATCC 8739 to Adapt to 11%NaCl

Introduction: Escherichia coli (E. coli) is a non-halophilic microbe and is used to indicate faecal contamination. Salt (sodium chloride, NaCl) is a common food additive and is used in preservatives to counter microbial growth. Previous studies had shown that pathogenic E. coli has a higher salt tolerance than non-pathogenic E. coli. The effect of how E. coli interacts with the salt present in the human diet is under-studied. Thus, it is important to investigate this relationship. Methods: In this study, we observed the genetic changes and growth kinetics of E. coli ATCC 8739 under 3% - 11% NaCl over 80 passages. Growth kinetics was estimated by generation time, cell density and minimum inhibitory concentration (MIC) of NaCl. Results: Our results suggested that E. coli was able to adapt from 1% NaCl to 11% NaCl with an increment of 1% NaCl per month. Our MIC results suggested that E. coli was able to grow at NaCl concentration of more than 7.5% based on the Area under Curve (AUC) from 5% at passage 44 (cultured in 5% NaCl) to 13% at passage 72 (cultured at 7% NaCl). Conclusion: We conclude that E. coli ATCC 8739 can be adapted to grow in 11% NaCl by incremental adaptation.