Responses to environmental stress have been described in Escherichia coli and Bacillus subtilis. These studies have shown that bacteria display elaborate responses to environmental stress which improve survival by altering bacterial physiology. The SOS response is induced when bacteria are threatened by the presence of agents that cause DNA damage which enhance the bacterium’s ability to repair DNA and inhibit cell division,. The stringent response, in the face of nutrient limitation, decreases protein synthesis and stimulates amino acid biosynthesis when protein synthesis substrates are scarce,[27-28]. Heat shock factors are expressed at raised temperatures that break down and restructure denatured proteins and also restore alterations to chromosomal topology that occur as a result of temperature,[29-30]. Finally components of the cold shock response have been shown to alter mRNA secondary structures, formed as a result of low temperature, which hinder the translational machinery,[31, 31].
The stress response to bile salts has been described in a number of bacteria. In Bacillus cereus bile salt stress was shown to invoke a general stress response comparative to that witnessed as a result of high bacterial densities and also a specific response that included a decrease in motility and the upregulation of multidrug exporters and regulators of transcription,. Other responses to bile salts have included proteins involved in repairing DNA and the synthesis of the cell