Bacteriophages, natural killers of bacteria, and plant secondary metabolites, such as condensed tannins, are potential agents for the control of foodborne pathogens. The first objective of this study evaluated the efficacy of a bacteriophage SA21RB in reducing pre-formed biofilms on stainless-steel produced by two Shiga toxin-producing Escherichia coli (STEC) strains, one from South Africa and the other from Canada. The second objective examined the anti-bacterial and anti-biofilm activity of condensed tannin (CT) from purple prairie clover and phlorotannins (PT) from brown seaweed against these strains. For 24-h-old biofilms, (O113:H21; 6.2 log10 colony-forming units per square centimeter (CFU/cm2) and O154:H10; 5.4 log10 CFU/cm2), 3 h of exposure to phage (1013 plaque-forming units per milliliter (PFU/mL)) reduced (p ≤ 0.05) the number of viable cells attached to stainless-steel coupons by 2.5 and 2.1 log10 CFU/cm2 for O113:H21 and O154:H10, respectively. However, as biofilms matured, the ability of phage to control biofilm formation declined. In biofilms formed for 72 h (O113:H21; 5.4 log10 CFU/cm2 and O154:H10; 7 log10 CFU/cm2), reductions after the same duration of phage treatment were only 0.9 and 1.3 log10 CFU/cm2 for O113:H21 and O154:H10, respectively. Initial screening of CT and PT for anti-bacterial activity by a microplate assay indicated that both STEC strains were less sensitive (p ≤ 0.05) to CT than PT over a concentration range of 25-400 µg/mL. Based on the lower activity of CT (25-400 µg/mL), they were not further examined. Accordingly, PT (50 µg/mL) inhibited (p ≤ 0.05) biofilm formation for up to 24 h of incubation at 22 °C, but this inhibition progressively declined over 72 h for both O154:H10 and O113:H21. Scanning electron microscopy revealed that both SA21RB and PT eliminated 24 h biofilms, but that both strains were able to adhere and form biofilms on stainless-steel coupons at longer incubation times. These findings revealed that phage SA21RB is more effective at disrupting 24 than 72 h biofilms and that PT were able to inhibit biofilm formation of both E. coli O154:H10 and O113:H21 for up to 24 h.

中文翻译：

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噬菌体和复合单宁对加拿大和南非产志贺毒素大肠杆菌生物膜的活性。


噬菌体、细菌的自然杀手和植物次生代谢物（例如缩合单宁）是控制食源性病原体的潜在药物。本研究的第一个目标是评估噬菌体 SA21RB 在减少不锈钢上预先形成的生物膜方面的功效，这两种生物膜由两种产志贺毒素大肠杆菌 (STEC) 菌株（一种来自南非，另一种来自加拿大）产生。第二个目的是检测紫色草原三叶草中的缩合单宁 (CT) 和棕色海藻中的叶皮单宁 (PT) 对这些菌株的抗菌和抗生物膜活性。对于 24 小时生物膜（O113:H21；6.2 log10 菌落形成单位每平方厘米 (CFU/cm2) 和 O154:H10；5.4 log10 CFU/cm2），暴露于噬菌体 3 小时（1013 噬菌斑形成单位）对于 O113:H21 和 O154:H10，每毫升单位 (PFU/mL)) 使附着在不锈钢试样上的活细胞数量分别减少 2.5 和 2.1 log10 CFU/cm2 (p ≤ 0.05)。然而，随着生物膜的成熟，噬菌体控制生物膜形成的能力下降。在形成 72 小时的生物膜中（O113:H21；5.4 log10 CFU/cm2 和 O154:H10；7 log10 CFU/cm2），在噬菌体处理相同持续时间后，O113:H21 和 O154:H10 的减少仅为 0.9 和 1.3 log10 CFU/cm2分别为O154:H10。通过微孔板测定对 CT 和 PT 的抗菌活性进行初步筛选表明，在 25-400 µg/mL 的浓度范围内，两种 STEC 菌株对 CT 的敏感性均低于 PT（p ≤ 0.05）。由于 CT 活性较低（25-400 µg/mL），因此未对其进行进一步检查。因此，PT (50 µg/mL) 在 22 °C 孵育长达 24 小时内抑制 (p ≤ 0.05) 生物膜形成，但对于 O154:H10 和 O113:H21，这种抑制作用在 72 小时内逐渐下降。 扫描电子显微镜显示，SA21RB 和 PT 都消除了 24 小时生物膜，但这两种菌株都能够在较长的孵育时间内在不锈钢试样上粘附并形成生物膜。这些发现表明，噬菌体 SA21RB 在破坏 24 小时生物膜方面比 72 小时生物膜更有效，并且 PT 能够抑制大肠杆菌 O154:H10 和 O113:H21 生物膜形成长达 24 小时。