Affiliation:
1. Institute of Technology, University of Tartu, Nooruse 1, Tartu 50411, Estonia
Abstract
ABSTRACT
The majority of cells transferred from stationary-phase culture into fresh medium resume growth quickly, while a few remain in a nongrowing state for longer. These temporarily nonproliferating bacteria are tolerant of several bactericidal antibiotics and constitute a main source of persisters. Several genes have been shown to influence the frequency of persisters in
Escherichia coli
, although the exact mechanism underlying persister formation is unknown. This study demonstrates that the frequency of persisters is highly dependent on the age of the inoculum and the medium in which it has been grown. The
hipA7
mutant had 1,000 times more persisters than the wild type when inocula were sampled from younger stationary-phase cultures. When started after a long stationary phase, the two displayed equal and elevated persister frequencies. The lower persister frequencies of
glpD
,
dnaJ
, and
surA
knockout strains were increased to the level of the wild type when inocula aged. The
mqsR
and
phoU
deletions showed decreased persister levels only when the inocula were from aged cultures, while
sucB
and
ygfA
deletions had decreased persister levels irrespective of the age of the inocula. A dependency on culture conditions underlines the notion that during screening for mutants with altered persister frequencies, the exact experimental details are of great importance. Unlike ampicillin and norfloxacin, which always leave a fraction of bacteria alive, amikacin killed all cells in the growth resumption experiment. It was concluded that the frequency of persisters depends on the conditions of inoculum cultivation, particularly its age, and the choice of antibiotic.
Publisher
American Society for Microbiology
Subject
Molecular Biology,Microbiology
Cited by
163 articles.
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