Zinc mediates resuscitation of lactic acid‐injuredEscherichia coliby relieving oxidative stress

Abstract

Aims Lactic acid is a natural antimicrobial in food industry, and also exists in fermented food. It was reported that sublethally injured Escherichia coli could survive in acidic conditions. When conditions become advantageous, injured E. coli can restore physiological function, which is a potential threat in food industry. Recovery is a necessary step for discriminating injured bacteria, but the resuscitation mechanism of injured bacteria is still unknown. Methods and Results In our study, sublethal lactic acid treatment (pH 4·2, 60 min) posed oxidative stress on E. coli by decrease of superoxide dismutase (SOD) activity and overproduction of reactive oxygen species (ROS). Zinc with low concentration (1·0 mmol l−1) significantly increased the recovery ratio of injured E.coli induced by lactic acid. The recovery ratios of injured cell in minimal A medium (minA) with 1·0 mmol l−1 zinc reached to that with 3·0 mmol l−1 catalase (CAT). Conversely, the addition of zinc chelator N, N, N′, N′‐tetrakis (2‐pyridylmethyl) decreased the recovery ratio. Zinc accelerated resuscitation of injured E. coli by improving SOD activity, and decreasing ROS production. Deletion of sodC encoding Cu/ZnSOD, katE/katG encoding CAT or regulating gene rpoS significantly decreased the recovery ratio. Among all of the mutants in this study, ΔrpoS and ΔsodC showed the lowest recovery ratio, which means they played significant roles in the process of resuscitation. Conclusion We provided direct evidence that zinc mediated resuscitation of lactic acid‐injured E. coli by relieving oxidative stress. Zinc can be used as a low‐cost and effective agent to improve recovery ratio and detection efficiency of injured bacteria. Significance and Impact of the Study Antibacterial agents are a challenge for bacteria, but bacteria can survive as a sublethally injured state under stresses. Using injured E. coli induced by lactic acid as a model organism, we validated the significant role of zinc on resuscitation of injured cells.

Synergetic Inactivation Mechanism of Protocatechuic Acid and High Hydrostatic Pressure against Escherichia coli O157:H7

“…When treated with PCA only, the CAT activity significantly increased to 109.18% ( p ≤ 0.05). Shi et al [ 23 ] found that at a molecular level that gene katG , which encodes KatG enzyme (a distinct CAT), is up-regulated in E. coli after a lactic acid treatment. After the PCA + HHP treatment, the CAT activity reached a maximum (128.76%) when the pressure reached 200 MPa, and then it decreased to 96.85%.…”

“…The pellets were each re-suspended in 10 mL 1/2-MIC PCA solution, and then cultured at 37 °C for 60 min at 120 rpm. The bacterial suspension after the PCA treatment was then treated under the same conditions as the HHP group [ 23 ]. For the 0 MPa treatment of the PCA + HHP group, cells treated with 1/2-MIC PCA, were then placed in the HHP equipment for 5 min at room temperature.…”

“…The E. coli O157:H7 NCTC 12900 strain, was purchased from the China Center of Industrial Culture Collection (Beijing, China) and stored at −20 • C. The strain was activated by incubating in NB at 37 • C for 7 h and then transferred to NB supplemented with 20% agar powder slant cultures and stored at 4 • C. After streak culturing in TSA, a loop of a single colony was then transferred to 50 mL TSB (pH 7.2), incubated in a shaker (TS-100B, Shanghai Tiancheng Experimental Instrument Manufacturing Co., Ltd., Shanghai, China) at 37 • C, 180 rpm for 6 h until the culture reached the middle period of logarithmic phase [23]. The bacterial pellet was harvested by centrifugation at 6000 rpm and 4 • C for 10 min, and then washed three times with PBS to remove the excess medium.…”

The effect of manganese and iron on mediating resuscitation of lactic acid-injured Escherichia coli

“…According to our previous experimental results, manganese and iron significantly improved the recovery ratio of lactic acid-injured E. coli, but whether and how manganese and iron promoted recovery by participating in oxidative stress response is still unclear (Shi et al 2017). In the genetic level, E. coli are more sensitive to acidic environmental stress after katE, katG, sodC or rpoS involved in oxidative stress resistance is knocked out (Shi et al 2019). In order to understand and design effective recovery condition of injured bacteria, the mechanisms of resuscitation need to be clarified.…”

“…In the genetic level, E. coli are more sensitive to acidic environmental stress after katE , katG , sodC or rpoS involved in oxidative stress resistance is knocked out (Shi et al . 2019). In order to understand and design effective recovery condition of injured bacteria, the mechanisms of resuscitation need to be clarified.…”