Department of Infectious Diseases, Heartlands Hospital, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK.
Department of Gastroenterology, Heartlands Hospital, University Hospitals Birmingham NHS Foundation Trust, Birmingham, UK.
J Med Microbiol. 2020 Apr;69(4):548-551. doi: 10.1099/jmm.0.001166.
The gene encodes a thermonuclease which is present in but not in coagulase-negative staphylococci (CoNS) and is the target of the rapid phenotypic thermonuclease test. The effect of gene variation in methicillin-resistant (MRSA) on the performance of PCR testing has been noted, although there are no reports about the effect of MRSA on the activity of the thermonuclease enzyme. Our goals were to examine the sensitivity and specificity of the thermonuclease test used to distinguish from CoNS cultured from blood. In addition, we aimed to assess differences in the sensitivity, specificity and accuracy of the thermonuclease test between methicillin-sensitive (MSSA) and MRSA isolates. We performed a retrospective analysis of 1404 isolates. Each isolate from a positive blood culture was identified as a Gram-positive coccus by microscopy then analysed with the thermonuclease test (Southern Group Laboratory) prior to confirmatory identification using VITEK microbial identification platforms (bioMérieux) and cefoxitin disc diffusion testing. Of 1331 samples included in the final analysis, 189 were thermonuclease-positive, of which 176 were identified as . Of the 1142 thermonuclease-negative samples, 13 were finally identified as , giving a sensitivity of 93.1 % (95 % confidence interval [CI] 88.5-96.3) and specificity of 98.9 % (95 % CI 98.1-99.4). Of the nine proven MRSA samples, eight were thermonuclease-positive, giving a sensitivity of 88.9 % (95 % CI 51.8-99.7). Thermonuclease test accuracy for MSSA and MRSA isolates was 98.1 % (95 % CI 97.2-98.8) versus 98.8 % (95 % CI 98.0-99.3), respectively. In the era of increasing use of molecular-based microbiology assays, the thermonuclease test remains a simple, inexpensive and robust test for the presumptive identification of cultured from blood, irrespective of methicillin sensitivity.
该基因编码一种热核酸酶，存在于金黄色葡萄球菌（金葡菌）中，但不存在于凝固酶阴性葡萄球菌（CoNS）中，是快速表型热核酸酶试验的靶标。已经注意到 基因变异对耐甲氧西林金黄色葡萄球菌（MRSA）PCR 检测性能的影响，尽管尚未有关于 MRSA 对热核酸酶活性影响的报道。我们的目标是检查用于区分血液培养的 CoNS 的热核酸酶试验的灵敏度和特异性。此外，我们旨在评估甲氧西林敏感金黄色葡萄球菌（MSSA）和 MRSA 分离株的热核酸酶试验的灵敏度、特异性和准确性之间的差异。我们对 1404 株分离株进行了回顾性分析。每个阳性血培养物的分离株通过显微镜检查鉴定为革兰氏阳性球菌，然后用热核酸酶试验（Southern Group Laboratory）进行分析，然后使用 VITEK 微生物鉴定平台（bioMérieux）和头孢西丁纸片扩散试验进行确认鉴定。在最终分析中包括 1331 个样本，189 个为热核酸酶阳性，其中 176 个被鉴定为 。在 1142 个热核酸酶阴性样本中，最终有 13 个被鉴定为 ，灵敏度为 93.1%（95%置信区间 [CI] 88.5-96.3），特异性为 98.9%（95% CI 98.1-99.4）。在 9 个证实的 MRSA 样本中，8 个为热核酸酶阳性，灵敏度为 88.9%（95% CI 51.8-99.7）。MSSA 和 MRSA 分离株的热核酸酶试验准确性分别为 98.1%（95% CI 97.2-98.8）和 98.8%（95% CI 98.0-99.3）。在越来越多地使用基于分子的微生物学检测的时代，热核酸酶试验仍然是一种简单、廉价且强大的试验，可用于鉴定从血液中培养的 ，而与耐甲氧西林敏感性无关。
