Table_2_The Combined Effect of Cold and Copper Stresses on the Proliferation and Transcriptional Response of Listeria monocytogenes.XLSX

Listeria monocytogenes is a foodborne pathogen that can cause severe disease in susceptible humans. This microorganism has the ability to adapt to hostile environmental conditions such as the low temperatures used by the food industry for controlling microorganisms. Bacteria are able to adjust their transcriptional response to adapt to stressful conditions in order to maintain cell homeostasis. Understanding the transcriptional response of L. monocytogenes to stressing conditions could be relevant to develop new strategies to control the pathogen. A possible alternative for controlling microorganisms in the food industry could be to use copper as an antimicrobial agent. The present study characterized three L. monocytogenes strains (List2-2, Apa13-2, and Al152-2A) adapted to low temperature and challenged with different copper concentrations. Similar MIC-Cu values were observed among studied strains, but growth kinetic parameters revealed that strain List2-2 was the least affected by the presence of copper at 8°C. This strain was selected for a global transcriptional response study after a 1 h exposition to 0.5 mM of CuSO4 × 5H2O at 8 and 37°C. The results showed that L. monocytogenes apparently decreases its metabolism in response to copper, and this reduction is greater at 8°C than at 37°C. The most affected metabolic pathways were carbohydrates, lipids and nucleotides synthesis. Finally, 15 genes were selected to evaluate the conservation of the transcriptional response in the other two strains. Results indicated that only genes related to copper homeostasis showed a high degree of conservation between the strains studied, suggesting that a low number of genes is implicated in the response to copper stress in L. monocytogenes. These results contribute to the understanding of the molecular mechanisms used by bacteria to overcome a combination of stresses. This study concluded that the application of copper in low concentrations in cold environments may help to control foodborne pathogens as L. monocytogenes in the industry.

单核细胞增生李斯特菌（Listeria monocytogenes）是一种食源性致病菌，可使易感人群罹患重症。该微生物可适应恶劣环境条件，例如食品工业为抑制微生物增殖而采用的低温环境。细菌可通过调控转录应答以适应胁迫环境，进而维持细胞稳态。解析单核细胞增生李斯特菌在胁迫条件下的转录应答机制，有助于开发防控该致病菌的全新策略。在食品工业中，使用铜作为抗菌剂是防控微生物污染的可行替代方案之一。本研究针对3株适应低温环境的单核细胞增生李斯特菌菌株（List2-2、Apa13-2及Al152-2A）开展实验，对其施加不同浓度的铜胁迫。供试菌株的铜最低抑菌浓度（MIC-Cu）水平相近，但生长动力学参数分析显示，在8℃条件下，菌株List2-2受铜胁迫的影响最小。研究选取该菌株，分别在8℃与37℃环境中，经0.5 mM五水硫酸铜（CuSO4·5H2O）处理1小时后，开展全局转录应答分析。结果显示，单核细胞增生李斯特菌在铜胁迫下会显著降低代谢水平，且该代谢抑制效应在8℃时较37℃时更为明显。受影响最为显著的代谢通路包括碳水化合物代谢、脂质合成及核苷酸合成通路。最后，研究选取15个基因，以评估另外两株菌株的转录应答保守性。结果表明，仅与铜稳态相关的基因在供试菌株间呈现高度保守性，这提示单核细胞增生李斯特菌中参与铜胁迫应答的基因数量较少。本研究结果有助于深入解析细菌应对多重胁迫的分子机制。本研究最终得出结论：在低温环境中应用低浓度铜制剂，可助力工业领域防控单核细胞增生李斯特菌等食源性致病菌。