当样品中大肠菌数量很少时,用常规的0.1 g样品(即10%食品匀浆1.0 ml)于90 mm的平皿上进行倾注平板作大肠菌群计数时,在实际工作中至少存在四个方面的问题。 1.如增大样品量,则培养基用量也必须加大以取得适宜的分散度。这在平板计数中往往不易作到,致使只能得出阳性或未检出的检验报告。 2.当其他细菌数量大时可能妨碍大肠菌群的菌落观察。例如靠近大肠杆菌生长的脱氨基细菌菌落,可影响酸度,从而使大肠菌的菌 When there is only a small amount of coliforms in the sample, there will be at least four in practice when using a conventional 0.1 g sample (ie 1.0 ml of 10% food homogenate) on a 90 mm plate for plate counting of coliforms Problems. 1. If the sample size is increased, the amount of medium used must also be increased to achieve the desired degree of dispersion. This is often not easy to do in plate counting, resulting in only positive or undetected test reports. 2. Large numbers of other bacteria may hinder colony observation of colonies. For example, colonies of deaminated bacteria that grow close to E. coli can affect acidity,