Study of exogenous oxidative stress response in Escherichia coli, Pseudomonas spp., Bacillus spp., and Salmonella spp.

Abstract

With a previous observation of Escherichia coli growth cessation with the supplementation of 3 mM hydrogen peroxide (H2O2) at the late log phase, the current study further demonstrated the consequences of the addition of an increased concentration (6 mM) of H2O2 and further extended the investigation on such an oxidant's impact on the growth of Salmonella spp., Pseudomonas spp., and Bacillus spp. Cell culturability was measured through the enumeration of colony-forming units (CFUs) on agar plates for up to 72 h. Subsequent changes in cell morphology and arrangements were monitored, and the cell viability was simultaneously retraced by spot tests. A sharp decline in the culturable cells of E. coli was observed after 48 h with a large mass of cell aggregates upon addition of H2O2, while Pseudomonas spp. lost viability after 36 h. Impaired morphology of such stressed cells was comparable to those of the untreated cells. Notably, Pseudomonas cells were more prone to oxidative damage compared to E. coli. In contrast, the impact of H2O2 was insignificant in the case of Salmonella spp. and Bacillus spp., suggestive of a stringent defense mechanism against oxidative stress.