Department of Animal Science, University of Connecticut, 302B Agricultural Biotechnology Laboratory, 1390 Storrs Road, U-4163, Storrs, CT, 06269-4163, USA.
Department of Animal Science, University of Connecticut, 302B Agricultural Biotechnology Laboratory, 1390 Storrs Road, U-4163, Storrs, CT, 06269-4163, USA.
Food Microbiol. 2025 Jan;125:104652. doi: 10.1016/j.fm.2024.104652. Epub 2024 Oct 5.
Listeria monocytogenes was the etiologic agent in nearly all recent outbreaks in North America attributed to pasteurized dairy products, whereas Escherichia coli O157 infections were responsible for most of the rare, yet serious complications from outbreaks involving unpasteurized dairy. This study determined the susceptibility of selected strains of L. monocytogenes and Shiga toxin-producing E. coli (STEC) to commercial phage preparations and their ability to control these pathogens in pasteurized and raw milk during 7-day storage at 7 °C. Both phage products demonstrated high lytic efficiency against 17 strains of L. monocytogenes whereas the efficiency of E. coli phages was more variable against 11 strains of O157 and non-O157 STEC. Broth microdilution assays identified effective endpoint multiplicities of infection (MOI) ranging from log 2.53 to 5.13, which differed between strains of L. monocytogenes and phage products. Mean log MOIs of E. coli phages against STEC also varied within and between products from 0.43 to 7.05. Despite these observations, the change in counts over time of three L. monocytogenes strains exposed to phage in pasteurized milk (log MOI 6) was similar with counts ∼ 4 log CFU/mL lower than control at day 7. Results for STEC O157 varied by strain but counts were lower than control in all cases by 72 h thorough day 7. Titers on isolates of both pathogens isolated from pasteurized milk indicated that the surviving populations were less susceptible to phage. The addition of a phage preparation to raw milk did not reduce populations of either pathogen or affect the change in counts of any strain over time when compared to control. Reduced efficacy in raw milk may be attributed to reduced phage binding as titers in raw milk decreased steadily (∼2 log PFU/mL) during storage. Commercial phage products may be a promising pathogen control intervention for pasteurized dairy products, warranting further investigation.
单核细胞增生李斯特菌是导致北美近期所有经巴氏杀菌乳制品传播的暴发的主要病原体，而大肠杆菌 O157 感染是导致极少数但严重的暴发相关并发症的主要原因，这些暴发涉及未经巴氏杀菌的乳制品。本研究测定了选定的单核细胞增生李斯特菌和产志贺毒素大肠杆菌（STEC）菌株对商业噬菌体制剂的敏感性，并评估了这些噬菌体制剂在 7°C 下对巴氏杀菌和生牛乳进行 7 天储存时控制这些病原体的能力。两种噬菌体产品对 17 株单核细胞增生李斯特菌的裂解效率均很高，而大肠杆菌噬菌体的效率对 11 株 O157 和非-O157 STEC 的菌株则差异较大。肉汤微量稀释法鉴定出有效的终点感染复数（MOI）范围为 log2.53 至 5.13，这在单核细胞增生李斯特菌菌株和噬菌体产品之间有所不同。针对 STEC 的大肠杆菌噬菌体的平均对数 MOI 也在产品之间和产品内从 0.43 到 7.05 变化。尽管存在这些观察结果，但在巴氏杀菌乳中暴露于噬菌体的 3 株单核细胞增生李斯特菌菌株的数量随时间的变化与对照相比，在第 7 天时计数降低了约 4 个对数 CFU/mL。O157 STEC 的结果因菌株而异，但在所有情况下，到第 7 天，计数均比对照低。从巴氏杀菌乳中分离出的两种病原体的分离物的效价表明，存活的种群对噬菌体的敏感性降低。与对照相比，在生牛乳中添加噬菌体制剂不会降低任何病原体的数量，也不会影响任何菌株的数量随时间的变化。在生牛乳中效果降低可能归因于噬菌体结合减少，因为在储存过程中噬菌体效价稳定下降（约 2 个对数 PFU/mL）。商业噬菌体产品可能是巴氏杀菌乳制品中一种有前途的病原体控制干预措施，值得进一步研究。
