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J Bacteriol. 2013 Feb;195(4):647-57. doi: 10.1128/JB.01397-12. Epub 2012 Nov 30.

Isolation of highly persistent mutants of Salmonella enterica serovar typhimurium reveals a new toxin-antitoxin module.

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  • 1Department of Veterinary Microbiology, Iowa State University, Ames, IA, USA.


Bacterial persistence is characterized by the ability of a subpopulation within bacterial cultures to survive exposure to antibiotics and other lethal treatments. The surviving persisters are not the result of genetic changes but represent epigenetic variants that are in a physiological state where growth is inhibited. Since characterization of persisters has been performed mainly in Escherichia coli K-12, we sought to identify mechanisms of persistence in the pathogen Salmonella enterica serovar Typhimurium. Isolation of new highly persistent mutants revealed that the shpAB locus (Salmonella high persistence) imparted a 3- to 4-order-of-magnitude increase in survival after ampicillin exposure throughout its growth phase and protected the population against exposure to multiple antibiotics. Genetic characterization revealed that shpAB is a newly discovered toxin-antitoxin (TA) module. The high-persistence phenotype was attributed to a nonsense mutation in the 3' end of the shpB gene encoding an antitoxin protein. Characteristic of other TA modules, shpAB is autoregulated, and high persistence depends on the Lon protease.

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