Department of Animal Sciences, Institute of Food and Agricultural Sciences, University of Florida, Gainesville 32606, USA.
J Dairy Sci. 2010 Mar;93(3):1098-104. doi: 10.3168/jds.2009-2433.
This study aimed to evaluate the effectiveness of 3 commercial bacterial inoculants at controlling Escherichia coli O157:H7 in corn silages during ensiling and feedout phases of silage production. A second objective was to determine whether the inoculants exhibited and transferred antibacterial activity against E. coli O157:H7 to the silages. Chopped corn forage was ensiled after treatment with the following: distilled water (control); 5 x 10(5) cfu/g of E. coli O157:H7 (EC); EC and 1 x 10(6) cfu/g of Pediococcus pentosaceus and Propionibacterium freudenreichii (EC+BII); EC and 1 x 10(6) cfu/g of Lactobacillus buchneri (EC+LB); and EC and 1 x 10(6) cfu/g of L. buchneri and P. pentosaceus (EC+B500). Each treatment was ensiled in triplicate in mini silos for 3, 7, 31, and 82 d and analyzed for pH and E. coli O157:H7 counts. Samples from d 82 were also analyzed for volatile fatty acids, lactate, and aerobic stability. Antibacterial activity of inoculants and silages was determined by the Kirby-Bauer disc diffusion test. The pH of silages from all treatments decreased below 4 within 3 d of ensiling and remained low until d 82. Therefore, E. coli O157:H7 was not detected in silages after any of the ensiling durations. Applying inoculants containing L. buchneri resulted in less lactate, more acetate, and greater aerobic stability compared with the control. Applying EC+BII containing P. freudenreichii did not increase propionate or aerobic stability. Subsamples of d 82 silages were reinoculated with 1 x 10(5) cfu/g of E. coli O157:H7 either immediately after silo opening on d 82 or after 144h of aerobic exposure (d 88), and E. coli were enumerated 24h later. All silages reinoculated with the pathogen on d 82 had similar, low pH values (<4) and no E. coli were detected 24h later. Control, EC, and EC+BII silages reinoculated with the pathogen after 144h of aerobic exposure had relatively greater pH values (4.71, 5.67, and 6.03, respectively) and E. coli counts (2.87, 6.73, and 6.87 log cfu/g, respectively) 24h later, whereas those treated with L. buchneri had low pH values (<4) and undetectable (EC+B500) or 10-fold lower (1.97, cfu/g; EC+LB) E. coli counts. All pure cultures of commercial bacterial inoculants exhibited antibacterial activity independent of pH against E. coli O157:H7, but the pH-independent activity did not persist in the treated silages, suggesting that E. coli elimination from silages was mediated by pH reduction.
本研究旨在评估 3 种商业细菌接种剂在青贮和青贮饲料生产过程中的饲料投喂阶段控制大肠杆菌 O157:H7 的效果。第二个目的是确定接种剂是否对大肠杆菌 O157:H7 表现出并转移了抗菌活性到青贮饲料中。切碎的玉米饲料在以下处理后进行青贮：蒸馏水（对照）；5 x 10(5)cfu/g 大肠杆菌 O157:H7（EC）；EC 和 1 x 10(6)cfu/g 戊糖片球菌和丙酸杆菌（EC+BII）；EC 和 1 x 10(6)cfu/g 布氏乳杆菌（EC+LB）；和 EC 和 1 x 10(6)cfu/g 布氏乳杆菌和戊糖片球菌（EC+B500）。每个处理在小型青贮窖中一式三份进行青贮 3、7、31 和 82 天，并分析 pH 和大肠杆菌 O157:H7 计数。82 天的样品还分析了挥发性脂肪酸、乳酸和有氧稳定性。接种剂和青贮饲料的抗菌活性通过 Kirby-Bauer 圆盘扩散试验确定。所有处理的青贮饲料的 pH 在青贮 3 天内降至 4 以下，并保持低至 82 天。因此，在任何青贮时间后，青贮饲料中均未检测到大肠杆菌 O157:H7。与对照相比，应用含有布氏乳杆菌的接种剂可导致较少的乳酸、更多的乙酸和更大的有氧稳定性。应用含有丙酸杆菌的 EC+BII 并没有增加丙酸或有氧稳定性。82 天的青贮饲料的亚样本立即在 82 天青贮窖打开后或在有氧暴露 144 小时后（88 天）用 1 x 10(5)cfu/g 大肠杆菌 O157:H7 重新接种，并在 24 小时后对大肠杆菌进行计数。82 天重新接种病原体的所有青贮饲料均具有相似的低 pH 值（<4），并且 24 小时后未检测到大肠杆菌。在有氧暴露 144 小时后用病原体重新接种的对照、EC 和 EC+BII 青贮饲料具有相对较高的 pH 值（分别为 4.71、5.67 和 6.03）和大肠杆菌计数（分别为 2.87、6.73 和 6.87 log cfu/g）24 小时后，而用布氏乳杆菌处理的 pH 值较低（<4），且未检测到（EC+B500）或低 10 倍（1.97，cfu/g；EC+LB）的大肠杆菌计数。所有商业细菌接种剂的纯培养物均表现出对大肠杆菌 O157:H7 的 pH 独立的抗菌活性，但在处理的青贮饲料中，这种 pH 独立的活性并未持续存在，这表明大肠杆菌从青贮饲料中的消除是通过 pH 值降低介导的。
