RpoS loss in Cronobacter sakazakii by propagation in the presence of non-preferred carbon sources

This study assessed whether propagation of four Cronobacter sakazakii strains in the presence of various non-preferred substrates (formate, fumarate, propionate, pyruvate and succinate) as sole carbon source can cause loss of RpoS functionality. Growth of C. sakazakii DPC 6525 in the presence of fumarate, propionate and succinate selected for loss of RpoS. rpoS mutants could not be obtained for C. sakazakii DPC 6522, DPC 6526 and DPC 6530. DPC 6525 showed lower growth ability in all carbon sources than the other strains tested and had higher mutagenesis rates, determined by plating on agar media supplemented with rifampicin, than DPC 6522 and DPC 6526 but much lower than DPC 6530. Results demonstrate that growth of C. sakazakii in non-preferred carbon sources can select for RpoS loss and suggest that certain strains are more predisposed to the loss of RpoS due to their reduced growth ability in environments of limited nutrients availability.