Institute of Technology, University of Tartu, Nooruse 1, Tartu 50411, Estonia.
J Bacteriol. 2011 Jul;193(14):3598-605. doi: 10.1128/JB.00085-11. Epub 2011 May 20.
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.
大多数从静止期培养物转移到新鲜培养基中的细胞会迅速恢复生长，而少数细胞会处于非生长状态更长时间。这些暂时非增殖的细菌对几种杀菌抗生素具有耐受性，是持久菌的主要来源。已经有几个基因被证明会影响大肠杆菌中持久菌的频率，尽管持久菌形成的确切机制尚不清楚。这项研究表明，持久菌的频率高度依赖于接种物的年龄和其生长的培养基。当从较年轻的静止期培养物中取样接种物时，hipA7 突变体的持久菌数量比野生型多 1000 倍。当从长时间的静止期开始后，两者的持久菌频率都相等且升高。当接种物老化时，glpD、dnaJ 和 surA 缺失株的较低持久菌频率增加到野生型水平。mqsR 和 phoU 缺失仅在接种物来自老化培养物时显示出较低的持久菌水平，而 sucB 和 ygfA 缺失则无论接种物的年龄如何，都表现出较低的持久菌水平。对培养条件的依赖性强调了这样一种观点，即在筛选具有改变的持久菌频率的突变体时，确切的实验细节非常重要。与始终使一部分细菌存活的氨苄青霉素和诺氟沙星不同，阿米卡星在恢复生长实验中杀死了所有细胞。因此，可以得出结论，持久菌的频率取决于接种物培养的条件，特别是其年龄，以及抗生素的选择。
