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金黄色葡萄球菌直接计数方法 如下: 吸取 1 : 10 混悬液,进行十倍递次稀释,根据样品污染情况,选择不同浓度的稀释液 1mL ,分别加入三块 Baird - Parker 平板,每个平板接种量分别为 0.3mL 、 0.3mL 、 0.4mL ,然后用灭菌 L 棒涂布整个平板。如水分不多吸收,可将平板放在 36±1°C 1h ,等水分蒸发后反转平皿置 36±1°C 培养。 在三个平板上点数周围有混浊带的黑色菌落,并从中任选 5 个菌落,分别接种血平板, 36±1°C24h 培养后进行染色镜检、血浆凝固酶试验,步骤同增菌培养法。 菌落计数:将三个平板中疑似金黄色葡萄球菌黑色菌落数相加,乘以血浆凝固酶阳性数,除以 5 ,再乘以稀释倍数,即可求出每克样品中金黄色葡萄球菌数。 实验结果: 稀释倍数 为10 2 , 三个平板中疑似金黄色葡萄球菌黑色菌落数 分别14、 15 、 21 , 血浆凝固酶阳性数 为4,则固体样品中 金黄色葡萄球菌 数为多少? (5分) 固体样品中 金黄色葡萄球菌 数: (14+15+21)×4÷5× 10 2 ÷1=4000个/克
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