Adaptation of Escherichia coli ATCC 8739 to 11% NaCl

Escherichia coli (E. coli) is a nonhalophilic microbe and used to indicate faecal contamination. Salt (sodium chloride, NaCl) is a common food additive and is used in preservatives to encounter microbial growth. The effect of how E. coli interacts with the salt present in the human diet is unclear. Thus, it is important to investigate this relationship. In order to adapt and survive the changes in the environment, E. coli may undergo halophilization. In this study, we observed the genetic changes and growth kinetics of E. coli ATCC 8739 under 3%–11% NaCl over 80 passages. Our results suggest that E. coli adapted to 1% increase in NaCl every month with a successful adaptation to 11% NaCl. Gram staining and PCR/RFLP showed that the cultures are Gram negative and the DNA profiles of all 4 replicates to be similar, suggesting that the cultures had not been contaminated. 1. Introduction Escherichia coli is a textbook example of nonhalophilic bacteria and is an indicator organism for faecal contamination of water as E. coli is a more consistent predictor of gastrointestinal illness than other bacterial indicators in water [1]. This corroborates Burton et al. [2] whom suggested that E. coli was a suitable predictor of Salmonella enterica serovar Newport in various freshwater sediments and has been observed to survive as long as or longer than Salmonella spp., thus, fulfilling its requirement as an indicator for pathogenic bacteria. In addition, the survival of E. coli is independent of the amount of organic matter [2]. This suggested that E. coli is a suitable indicator as it can survive in media of different nutritional richness. Previous studies [3–6] on the adaptation and evolution of E. coli were carried out using antibiotics and drugs. However, common food additive such as salt, which is used to preserve food and inhibit microorganisms, is less understood in terms of E. coli’s adaptive mechanism although recent studies [7, 8] had suggested that E. coli is able to adapt to food additives over extended culture. This suggests that E. coli may be able to adapt to higher concentrations of food additives but this has yet to be studied. Doudoroff [9] demonstrated that the viable count of E. coli previously cultured in ordinary fresh water media and then transferred to saline nutrient solutions remained at a constant up to 7% NaCl concentration. The viable count dropped progressively with further increase in concentration suggesting that E. coli is nonhalophilic and 7% NaCl is bacteriostatic. Hrenovic and Ivankovic [10] reported that the growth of E. coli is