Exponential Phase Virulence Genes May be Responsible for Inducing Shigellosis Infection

Our current study may suggest that shigellosis infections caused by Shigella flexneri may be initiated in the exponential phase of microbial growth due to dominance of early induction of virulence genes. Shigella flexneri are gram-negative bacteria that invade the colonic and rectal epithelium causing 1.1 million deaths annually. We evaluated the optimal pH growth of S. flexneri 2a strain (ATC29903) in vitro and determined the relative expressions of virulent gene, virF, and glutamate-dependent acid resistance (GDAR) pathway genes, gadB and gadC, which cause the microorganism to propagate. S. flexneri was grown in LB broth in vitro at pH 5.0, 7.0, and 8.0. Our results revealed that S. flexneri had the largest growth rates at pH 7.0 and 8.0 with the highest log number of cells obtained at pH 8.0. For all samples, exponential phase started at 2 hours while stationary phase began between 4 and 6 hours. Even though each treatment started at a different pH level, the data showed a consistent pH (4.5-4.8) in all groups after 6 hours of incubation. Based on our results, we can conclude that gadB, gadC, and virF genes are induced during exponential phase; and can potentially influence bacterial growth rate, which in turn aids in its invasive activity and possibly the cause of Shigellosis infections