Shigella modulation of polyamines during the invasion of host cells

Polyamines are small molecules found in all cells and associated with a wide variety of physiological processes. In bacterial pathogens the modulation of polyamine content could represent a strategy to optimize bacterial fitness within the host. Shigella, the etiological agent of bacillary dysentery, in contrast to its innocuous ancestor Escherichia coli, has a polyamine profile characterized by high level of intracellular spermidine. To understand the role of polyamines in the Shigella-host interaction, we analysed the expression of host cell genes involved in the biogenesis and back-conversion of polyamines during Shigella infection. Preliminary data indicate that the acetyl polyamine oxidase (APAO) is induced at early stages of Shigella infection, while induction of the spermine/spermidine acetyltransferase and of the spermine oxidase is detected later during the infection. These observations lead us to speculate that the early release of H2O2 as secondary product of APAO activity might represent a signal for Shigella to activate the expression of mdtJI efflux pump operon in order to export bacterial polyamines which have a scavenger function during oxidative stress conditions.