Saint Martin Cédric, Caccia Nelly, Darsonval Maud, Gregoire Marina, Combeau Arthur, Jubelin Grégory, Dubois-Brissonnet Florence, Leroy Sabine, Briandet Romain, Desvaux Mickaël
Université Paris-Saclay, INRAE, AgroParisTech, MICALIS Institute, 78350, Jouy-en-Josas, France.
INRAE, UCA, UMR0454 MEDIS, 63000, Clermont-Ferrand, France.
NPJ Sci Food. 2023 Oct 14;7(1):55. doi: 10.1038/s41538-023-00229-8.
Functional diversity within isogenic spatially organised bacterial populations has been shown to trigger emergent community properties such as stress tolerance. Considering gadB gene encoding a key glutamate decarboxylase involved in E. coli tolerance to acidic conditions, we investigated its expression in hydrogels mimicking the texture of some structured food matrices (such as minced meat or soft cheese). Taking advantage of confocal laser scanning microscopy combined with a genetically-engineered dual fluorescent reporter system, it was possible to visualise the spatial patterns of bacterial gene expression from in-gel microcolonies. In E. coli O157:H7 microcolonies, gadB showed radically different expression patterns between neutral (pH 7) or acidic (pH 5) hydrogels. Differential spatial expression was determined in acidic hydrogels with a strong expression of gadB at the microcolony periphery. Strikingly, very similar spatial patterns of gadB expression were further observed for E. coli O157:H7 grown in the presence of L. lactis. Considering the ingestion of contaminated foodstuff, survival of E. coli O157:H7 to acidic stomachal stress (pH 2) was significantly increased for bacterial cells grown in microcolonies in acidic hydrogels compared to planktonic cells. These findings have significant implications for risk assessment and public health as they highlight inherent differences in bacterial physiology and virulence between liquid and structured food products. The contrasting characteristics observed underscore the need to consider the distinct challenges posed by these food types, thereby emphasising the importance of tailored risk mitigation strategies.
同基因空间组织的细菌群体中的功能多样性已被证明会引发诸如应激耐受性等新出现的群落特性。考虑到gadB基因编码一种参与大肠杆菌耐酸性的关键谷氨酸脱羧酶，我们研究了其在模拟某些结构化食品基质（如碎肉或软奶酪）质地的水凝胶中的表达。利用共聚焦激光扫描显微镜结合基因工程双荧光报告系统，可以可视化凝胶内微菌落中细菌基因表达的空间模式。在大肠杆菌O157:H7微菌落中，gadB在中性（pH 7）或酸性（pH 5）水凝胶中表现出截然不同的表达模式。在酸性水凝胶中，gadB在微菌落周边强烈表达，从而确定了差异空间表达。引人注目的是，在乳酸乳球菌存在下生长的大肠杆菌O157:H7也观察到了非常相似的gadB表达空间模式。考虑到摄入受污染的食品，与浮游细胞相比，在酸性水凝胶中微菌落中生长的大肠杆菌O157:H7细胞对酸性胃部应激（pH 2）的存活率显著提高。这些发现对风险评估和公共卫生具有重要意义，因为它们突出了液体和结构化食品产品之间细菌生理学和毒力的内在差异。观察到的对比特征强调了需要考虑这些食品类型带来的不同挑战，从而强调了量身定制的风险缓解策略的重要性。
