Environmental Factors Regulate the hlyE Gene Expression in Both S. typhi and E. coli in a Similar Way to Display Haemolytic Activity

Abstract

Haemolysin (HlyE) is an essential virulence factor of Salmonella, Escherichia coli and other enteric bacteria. Although, a substantial degree of haemolytic activity is not seen under normal culture conditions in these organisms, however, the non-haemolytic E. coli K-12 showed significant haemolytic activity under stress conditions. To confirm this phenomenon in other enteric bacteria, in this study, the production of haemolysin in Salmonella enterica serovar Typhi under stress conditions, like oxygen and glucose starvations in vitro was investigated during March-December 2015. For this, S. typhi was cultured under oxygen or glucose starvation condition separately and this organism showed high haemolytic activity. The activity was found to be much higher when both the conditions were applied together. Also, the role of the transcription factor SlyA of S. typhi was investigated on induction of haemolytic activity. When E. coli K-12 was transformed with plasmid containing the gene of SlyA, the recombinant bacteria without any starvation condition, also showed similar haemolytic activity that was exhibited by S. typhi grown under oxygen and glucose starvation conditions. All these findings suggest that both environmental factors like oxygen or glucose starvation and overexpression of the transcription factor SlyA have important role in inducing hlyE gene expression in S. typhi.