临床咽拭子标本反复冻融对肺炎支原体分离效果的影响

Effect of repeated freeze-thaw on culture and isolation of Mycoplasma pneumoniae from clinical throat swab specimen

目的了解临床呼吸道标本反复冻融对肺炎支原体分离培养的影响,促进肺炎支原体临床标本分离培养工作的开展。方法选取2008-2009年北京临床医院150份肺炎病例咽拭子标本,使用液体培养并通过颜色变化单位(CCU)测定法检测标本中活菌,对1～4次冻融样本的阳性培养率和/或活菌量进行分析。结果临床咽拭子标本(200μl)中肺炎支原体携带量主要在0～103CCU之间。带菌量≤10 CCU的标本占培养阳性标本的40%左右,此类标本带菌量为临界培养检测限,经每次冻融会造成约1/4的阳性标本培养转阴。带菌量>10 CCU的标本,经3次反复冻融后均培养阳性,且CCU计数无明显变化,但培养阳性时间平均每次延长14 h左右。结论鉴于反复冻融对低病原体含量样品分离率的明显影响和对样品培养所需时间的明显延长,可能是影响临床样本支原体分离率的重要因素,应在样品分离培养前避免样品的反复冻融。

Objective To investigate the effect of repeated freeze-thaw on the culture and isolation of Mycoplasma pneumoniae （M. pneumoniae） from throat swab specimen and improve the isolation of M. pneumoniae from clinical specimen. Methods A total of 150 throat swabs were taken from the pneumonia patients in hospitals in Beijing. After culture the viable organism in these specimens were detected by color changing unit （CCU） assay, the positive culture rate and/or viable organism amount were analyzed for repeated freeze-thaw specimens （ 1 to 4 times）. Results There were about 0 -103CCU of M, pneumoniae in each 200 μl clinical swab specimen, The specimens with M, pneumoniae less than 10 CCU accounted for 40% of the total positive specimens and 25% of such specimens turned to be negative after 1 time freeze-thaw. After three times freeze-thaw, specimens with more than 10 CCU of M. pneumoniae had no significant change in CCU count, but which needed about 14 hours for prolonged incubation. Conclusion Due to the organism＇s sensitivity to repeated freeze-thaw, the freeze-thaw of clinical specimen should he avoided before culture.