Cunniffe J G, Whitby-Strevens S, Wilcox M H
Clinical Microbiology and Public Health Laboratory, Addenbrooke's Hospital, Cambridge.
J Clin Pathol. 1996 Mar;49(3):249-53. doi: 10.1136/jcp.49.3.249.
To determine the effect of pH changes occurring in cerebrospinal fluid (CSF) after sampling on the viability of meningitis causing bacteria, and on the performance of agglutination assays used for the rapid detection of bacterial antigens.
The pH of CSF collected via lumbar puncture was measured by various methods, and the effects of the following different incubation conditions on subsequent changes were determined: air at 4 degrees C; air at room temperature (22 degrees C); air at 37 degrees C; and air with 5% CO2 at 37 degrees C. The growth/survival in pooled CSF of 15 bacterial isolates collected from 74 patients with meningitis was assessed in these incubation conditions over 24 hours. The effects of pH changes in the CSF on the sensitivity of two latex agglutination and one co-agglutination kits for detecting Haemophilus influenzae, Neisseria meningitidis groups B and C, and Streptococcus pneumoniae were determined.
The measured pH of CSF was highly affected by the method used and particularly the time delay between patient sampling and assay. Measured pH values at the time of sampling (mean 7.5) increased rapidly within 60 seconds by about one unit. CSF pH continued to increase during incubation in all tested conditions (up to approximately pH 10), with the exception of in air with 5% CO2 at 37 degrees C where pH changes were reversible and near physiological values were attained. Bacterial survival for all species tested was poorest in CSF incubated in air at 37 degrees C and best following exposure to air with 5% CO2 at 37 degrees C. Agglutination in rapid antigen detection kits with CSF incubated in air as opposed to air with 5% CO2 generally took longer to occur and in some instances was less prominent. In one case a false negative result was obtained with CSF seeded with N meningitidis group B incubated in the former but not the latter conditions.
CSF pH increases after patient sampling are minimised and/or mostly reversed by incubation in an atmosphere containing 5% CO2. CSF samples should ideally be placed in such an atmosphere as soon as possible after collection, and left there until laboratory processing occurs, to reduce the detrimental effects of pH stress on bacterial survival. pH increases may also reduce the likelihood of obtaining a positive result in rapid antigen detection assays.
确定采样后脑脊液（CSF）中发生的pH变化对引起脑膜炎细菌的生存能力以及用于快速检测细菌抗原的凝集试验性能的影响。
通过多种方法测量经腰椎穿刺采集的脑脊液的pH值，并确定以下不同孵育条件对后续变化的影响：4℃空气；室温（22℃）空气；37℃空气；以及37℃含5%二氧化碳的空气。在这些孵育条件下，对从74例脑膜炎患者中分离出的15株细菌在混合脑脊液中的生长/存活情况进行了24小时评估。确定了脑脊液pH变化对两种乳胶凝集试验试剂盒和一种协同凝集试验试剂盒检测流感嗜血杆菌、B群和C群脑膜炎奈瑟菌以及肺炎链球菌敏感性的影响。
脑脊液的测量pH值受所用方法的高度影响，特别是患者采样与检测之间的时间延迟。采样时测得的pH值（平均7.5）在60秒内迅速上升约一个单位。在所有测试条件下孵育期间，脑脊液pH值持续上升（最高可达约pH 10），但在37℃含5%二氧化碳的空气中，pH变化是可逆的，且接近生理值。在37℃空气中孵育的脑脊液中，所有测试菌种的细菌存活率最差，而在37℃含5%二氧化碳的空气中暴露后存活率最佳。与在含5%二氧化碳的空气中孵育的脑脊液相比，在空气中孵育的脑脊液用于快速抗原检测试剂盒时，凝集反应通常发生得更慢，在某些情况下也不那么明显。在一个案例中，在前一种而非后一种条件下孵育的接种B群脑膜炎奈瑟菌的脑脊液获得了假阴性结果。
患者采样后脑脊液pH值的升高可通过在含5%二氧化碳的气氛中孵育而降至最低和/或大多逆转。脑脊液样本理想情况下应在采集后尽快置于这样的气氛中，并保持在那里直至进行实验室处理，以减少pH应激对细菌存活的有害影响。pH值升高也可能降低快速抗原检测试验获得阳性结果的可能性。
