Department of Agricultural, Forest and Food Sciences, University of Turin, Grugliasco, Italy.
Departamento de Veterinária, Universidade Federal de Viçosa, Viçosa, Brazil.
Int J Food Microbiol. 2019 Nov 2;308:108291. doi: 10.1016/j.ijfoodmicro.2019.108291. Epub 2019 Aug 6.
Biocontrol of Staphylococcus aureus by lactic acid bacteria can be considered as a feasible alternative to the use of chemicals in foods, but the mechanisms underlying this antagonistic interaction remains poorly understood. This study aimed to evaluate the impact of a LAB species (Enterococcus faecalis) over the growth, enterotoxin production and gene expression of S. aureus under experimental conditions. E. faecalis 41FL1 and S. aureus ATCC 29213 were inoculated isolated and together in brain heart infusion (BHI) at 30 °C and in a fresh cheese model at 15 °C: microbial populations were monitored by culture plating, production of classical staphylococcal enterotoxins (SEs) was verified by an ELISA assay, expression of S. aureus genes (virulence, transcriptional regulation and central carbon metabolism) was investigated by quantitative real-time PCR, and pH and contents of water-soluble metabolites in both matrices were measured. S. aureus growth was inhibited in co-cultures assays, with a 2.02-log reduction in BHI and a 3.39-log reduction in cheese model compared to respective single cultures. Classical SEs were detected in S. aureus single culture assays (BHI and cheese), in BHI inoculated with both strains after 48 h of incubation, but not detected in co-inoculated cheeses. pH in all matrices containing E. faecalis reached lower values than in matrices containing S. aureus alone, due to lactate production by E. faecalis. Expression of genes coding for transcription regulators (ccpA and rex) and enzymes involved in central carbon metabolism (alsD and citZ) was mostly upregulated in co-inoculated cheeses, whereas expression of several virulence determinants (agrC, hld, hla, entA and spa) was strongly downregulated. This study provides relevant data on the behaviour of S. aureus in the presence of competing microbiota and support the use of controlled population dominance by LAB as an effective biopreservation strategy to ensuring food safety.
乳酸菌对金黄色葡萄球菌的生物防治作用可以被视为食品中使用化学物质的可行替代品，但这种拮抗相互作用的机制仍知之甚少。本研究旨在评估 LAB 物种（粪肠球菌 41FL1）对金黄色葡萄球菌在实验条件下的生长、肠毒素产生和基因表达的影响。粪肠球菌 41FL1 和金黄色葡萄球菌 ATCC 29213 分别在脑心浸液（BHI）中于 30°C 和新鲜奶酪模型中于 15°C 下接种和共接种：通过培养平板监测微生物种群，通过 ELISA 测定法验证经典的葡萄球菌肠毒素（SE）的产生，通过定量实时 PCR 研究金黄色葡萄球菌基因（毒力、转录调控和中心碳代谢）的表达，并测量两种基质的 pH 值和水溶性代谢物含量。在共培养试验中，金黄色葡萄球菌的生长受到抑制，与单独培养相比，BHI 中的减少了 2.02 对数，奶酪模型中减少了 3.39 对数。在金黄色葡萄球菌单独培养试验（BHI 和奶酪）中检测到经典 SE，在接种两种菌株 48 小时后在 BHI 中检测到 SE，但在共接种奶酪中未检测到 SE。由于粪肠球菌产生乳酸，所有含有粪肠球菌的基质的 pH 值均低于单独含有金黄色葡萄球菌的基质。在共接种奶酪中，大多数编码转录调节因子（ccpA 和 rex）和参与中心碳代谢的酶（alsD 和 citZ）的基因表达上调，而许多毒力决定因素（agrC、hld、hla、entA 和 spa）的表达则强烈下调。本研究提供了金黄色葡萄球菌在竞争微生物群存在下的行为的相关数据，并支持使用 LAB 控制群体优势作为确保食品安全的有效生物保鲜策略。
