Department of Food, Nutrition, and Packaging Sciences, Clemson University, Clemson, South Carolina, USA.
J Appl Microbiol. 2022 Jun;132(6):4531-4543. doi: 10.1111/jam.15528. Epub 2022 Mar 29.
To isolate the slow-growing or viable but non-culturable competitive exclusion (CE) microorganisms from composts and then verify the anti-Listeria monocytogenes activities of those CE isolates in compost.
CE strains were isolated from composts using double- or triple-layer agar methods, purified, and then characterized. Both compost extracts and solid compost samples were spiked with a cocktail of 3 L. monocytogenes strains which were co-inoculated with or without CE strain cocktail and incubated at both 22 and 35°C for 168 h. Results indicated that the addition of resuscitation promoting factor (Rpf) promoted the growth of slow-growing species from composts. About 50% of the isolated CE strains (n = 40) were identified as Bacillus spp., 17 strains can inhibit more than 10 tested L. monocytogenes strains, and nine strains were motile and competitive biofilm formers. In compost extracts, the growth potentials of L. monocytogenes were reduced up to 2.2 logs when co-culturing with CE strains. In compost samples, the addition of CE strains reduced L. monocytogenes population by ca. 1.3 log CFU/g at 22°C after 24-168 h incubation.
Our modified double/triple-layer agar procedure with Rpf as growth supplement coupled with spot-on-lawn testing can be a quick and efficient method for isolating CE candidates from composts. The efficacy of CE strains against L. monocytogenes in compost extracts and compost samples was affected by compost type, nutrient level, and incubation temperature.
Compost is a rich source of CE microorganisms, and compost-adapted CE microorganisms have the potential as a biological agent to control L. monocytogenes in agricultural environments.
从堆肥中分离出生长缓慢或存活但不可培养的竞争排斥（CE）微生物，然后验证这些 CE 分离株在堆肥中抗李斯特菌的活性。
使用双层或三层琼脂法从堆肥中分离出 CE 菌株，进行纯化后进行鉴定。将堆肥提取物和固体堆肥样品与李斯特菌混合鸡尾酒（共接种或不接种 CE 菌株鸡尾酒）一起接种，并在 22°C 和 35°C 下孵育 168 小时。结果表明，添加复苏促进因子（Rpf）可促进来自堆肥的缓慢生长物种的生长。大约 50%（n=40）的分离 CE 菌株被鉴定为芽孢杆菌属，17 株可抑制超过 10 株测试的李斯特菌，9 株为运动和竞争生物膜形成者。在堆肥提取物中，当与 CE 菌株共培养时，李斯特菌的生长潜力降低了 2.2 个对数级。在堆肥样品中，在 22°C 孵育 24-168 小时后，添加 CE 菌株可使李斯特菌减少约 1.3 个对数 CFU/g。
我们使用改良的双层/三层琼脂程序和 Rpf 作为生长补充物，结合点植法，可以快速有效地从堆肥中分离出 CE 候选物。CE 菌株对堆肥提取物和堆肥样品中李斯特菌的功效受堆肥类型、营养水平和孵育温度的影响。
堆肥是 CE 微生物的丰富来源，适应堆肥的 CE 微生物具有作为生物制剂控制农业环境中李斯特菌的潜力。
