Ercibengoa Maria
Clin Lab. 2021 Mar 1;67(3). doi: 10.7754/Clin.Lab.2020.200438.
Streptococcus pneumoniae identification has traditionally been based on two biochemical tests, susceptibility of pneumococci to optochin and solubility in bile-salt solution. Due to slowness and sometimes difficulty in interpretation, the bile solubility test has fallen into disuse. The main objective of this work was to assess the current effectiveness of the optochin susceptibility test in pneumococcal identification in clinical practice.
Overall 126 viridans group streptococci consecutively isolated from respiratory samples were analyzed using the optochin susceptibility test by picking one colony from the culture. Sixty-two were initially considered optochin susceptible, and 64 were considered optochin resistant and analyzed with the bile solubility test. If a discrepancy between the tests was observed (i.e., whether an isolate was optochin susceptible and bile insoluble or optochin resistant and bile soluble), then the optochin susceptibility test was repeated, adjusting the inoculum to a McFarland standard of 0.5. Species were identified by sequencing the lytA and recA genes.
Twelve discrepancies were initially observed. The result of the repeated optochin test showed that the initial optochin test of 4 isolates had been wrongly interpreted. Of the remaining 8 discrepancies, 2 optochin-resistant bile-soluble isolates were identified by gene sequencing as S. pneumoniae, and of the 6 optochin-susceptible bile-nonsoluble isolates, 3 were identified as Streptococcus mitis and 3 as Streptococcus pseudopneumoniae.
The optochin test correctly identified 90.5% of all recent viridans group streptococci clinical isolates which include both optochin susceptible (62/126 = 49.2%) and optochin resistant (64/126 = 50.8%) strains. Of the group of optochin susceptible viridans, 87.5% were correctly identified, and 93.5% of the optochin resistant group were correctly identified. However, this technique does not correctly differentiate between S. pneumoniae from other viridans group streptococci in the clinical setting. Additional testing is needed for that identification.
肺炎链球菌的鉴定传统上基于两项生化试验，即肺炎球菌对奥普托欣的敏感性以及在胆盐溶液中的溶解性。由于胆盐溶解试验速度慢且有时难以解读，该试验已不再使用。这项工作的主要目的是评估奥普托欣敏感性试验在临床实践中鉴定肺炎球菌的当前有效性。
从呼吸道样本中连续分离出126株草绿色链球菌，通过从培养物中挑取一个菌落，使用奥普托欣敏感性试验进行分析。最初62株被认为对奥普托欣敏感，64株被认为对奥普托欣耐药，并进行胆盐溶解试验分析。如果观察到试验之间存在差异（即分离株对奥普托欣敏感但胆盐不溶，或对奥普托欣耐药但胆盐可溶），则重复奥普托欣敏感性试验，将接种物调整至麦氏比浊标准0.5。通过对lytA和recA基因进行测序来鉴定菌种。
最初观察到12处差异。重复奥普托欣试验的结果表明，4株分离株的初始奥普托欣试验被错误解读。在其余8处差异中，2株对奥普托欣耐药且胆盐可溶的分离株经基因测序鉴定为肺炎链球菌，在6株对奥普托欣敏感且胆盐不溶的分离株中，3株鉴定为缓症链球菌，3株鉴定为假肺炎链球菌。
奥普托欣试验正确鉴定了所有近期草绿色链球菌临床分离株中的90.5%，这些分离株包括对奥普托欣敏感（62/126 = 49.2%）和对奥普托欣耐药（64/126 = 50.8%）的菌株。在对奥普托欣敏感的草绿色链球菌组中，87.5%被正确鉴定，在对奥普托欣耐药的组中，93.5%被正确鉴定。然而，在临床环境中，这项技术无法正确区分肺炎链球菌与其他草绿色链球菌。为此类鉴定需要进行额外检测。
