Mariam Solomon H, Zegeye Nigus, Aseffa Abraham, Howe Rawleigh
Section of Microbiology, Aklilu Lemma Institute of Pathobiology, Addis Ababa University, P.O. Box 1176, Addis Ababa, Ethiopia.
Armauer Hansen Research Institute (AHRI), Addis Ababa, Ethiopia.
BMC Microbiol. 2017 Feb 15;17(1):35. doi: 10.1186/s12866-017-0944-3.
BACKGROUND: Food-borne infections cause huge economic and human life losses. Listeria monocytogenes and Salmonella enterica serovar Enteritidis are among the top ranking pathogens causing such losses. Control of such infections is hampered by persistent contamination of foods and food-processing environments, resistance of pathogens to sanitizing agents, existence of heterogeneous populations of pathogens (including culturable and viable but non-culturable cells) within the same food items, and inability to detect all such pathogens by culture-based methods. Modern methods such as flow cytometry allow analyses of cells at the single cell level within a short time and enable better and faster detection of such pathogens and distinctions between live and dead cells. Such methods should be complemented by control strategies including the use of beneficial bacteria that produce metabolites capable of inhibiting food-borne pathogens. In this study, broth cultures of lactic acid bacteria (LAB) isolated from fermented milk were tested for production of substances capable of inhibiting L. monocytogenes and S. Enteritidis in co-culture with LAB by assessment of colony-forming units (CFU) and live:dead cell populations by flow cytometry. RESULTS: The LAB isolates belonged to the species Lactococcus lactis, Enterococcus faecalis and Enterococcus faecium. Some LAB were effective in inhibition. Plating indicated up to 99% reduction in CFU from co-cultures compared to control cultures. Most of the bacteria in both cultures were in the viable but non-culturable state. The flow data showed that there were significantly higher dead cell numbers in co-cultures than in control cultures, indicating that such killing was caused by diffusible substances produced by the LAB cultures. CONCLUSION: This study showed that metabolites from selected local LAB species can be used to significantly reduce pathogen load. However, conditions of use and application need to be further investigated and optimized for large-scale utilization.
背景:食源性感染造成巨大的经济损失和人员伤亡。单增李斯特菌和肠炎沙门氏菌是导致此类损失的主要病原体。食品和食品加工环境的持续污染、病原体对消毒剂的抗性、同一食品中病原体异质群体的存在(包括可培养和活的但不可培养的细胞)以及基于培养的方法无法检测到所有此类病原体,都阻碍了对这些感染的控制。诸如流式细胞术等现代方法能够在短时间内对单细胞水平的细胞进行分析,并能更好、更快地检测此类病原体以及区分活细胞和死细胞。此类方法应辅以控制策略,包括使用能产生抑制食源性病原体代谢物的有益细菌。在本研究中,通过评估菌落形成单位(CFU)以及利用流式细胞术分析活细胞与死细胞群体,对从发酵乳中分离出的乳酸菌(LAB)肉汤培养物与LAB共培养时抑制单增李斯特菌和肠炎沙门氏菌的物质产生情况进行了测试。 结果:分离出的LAB菌株属于乳酸乳球菌、粪肠球菌和屎肠球菌。一些LAB具有有效的抑制作用。平板计数表明,与对照培养物相比,共培养物中的CFU减少了高达99%。两种培养物中的大多数细菌都处于活的但不可培养的状态。流式细胞术数据显示,共培养物中的死细胞数量显著高于对照培养物,这表明这种杀灭是由LAB培养物产生的可扩散物质引起的。 结论:本研究表明,所选本地LAB物种的代谢物可用于显著降低病原体载量。然而,使用条件和应用方式需要进一步研究并优化,以便大规模利用。
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