Molecular Genetics and Antimicrobial Resistance Unit, International Center for Microbial Genomics, Universidad El Bosque, Bogota, Colombia.
Center for Antimicrobial Resistance and Microbial Genomics, McGovern Medical School, University of Texas Health Science Center, Houston, Texas, USA.
J Clin Microbiol. 2021 Mar 19;59(4). doi: 10.1128/JCM.01938-20.
The cefazolin inoculum effect (CzIE) has been associated with therapeutic failures and mortality in invasive methicillin-susceptible (MSSA) infections. A diagnostic test to detect the CzIE is not currently available. We developed a rapid (∼3 h) CzIE colorimetric test to detect staphylococcal-β-lactamase (BlaZ) activity in supernatants after ampicillin induction. The test was validated using 689 bloodstream MSSA isolates recovered from Latin America and the United States. The cefazolin MIC determination at a high inoculum (10 CFU/ml) was used as a reference standard (cutoff ≥16 μg/ml). All isolates underwent genome sequencing. A total of 257 (37.3%) of MSSA isolates exhibited the CzIE by the reference standard method. The overall sensitivity and specificity of the colorimetric test was 82.5% and 88.9%, respectively. Sensitivity in MSSA isolates harboring type A BlaZ (the most efficient enzyme against cefazolin) was 92.7% with a specificity of 87.8%. The performance of the test was lower against type B and C enzymes (sensitivities of 53.3% and 72.3%, respectively). When the reference value was set to ≥32 μg/ml, the sensitivity for isolates carrying type A enzymes was 98.2%. Specificity was 100% for MSSA lacking The overall negative predictive value ranged from 81.4% to 95.6% in Latin American countries using published prevalence rates of the CzIE. MSSA isolates from the United States were genetically diverse, with no distinguishing genomic differences from Latin American MSSA, distributed among 18 sequence types. A novel test can readily identify most MSSA isolates exhibiting the CzIE, particularly those carrying type A BlaZ. In contrast to the MIC determination using high inoculum, the rapid test is inexpensive, feasible, and easy to perform. After minor validation steps, it could be incorporated into the routine clinical laboratory workflow.
头孢唑林接种体效应（CzIE）与侵袭性耐甲氧西林金黄色葡萄球菌（MSSA）感染的治疗失败和死亡率有关。目前尚无检测 CzIE 的诊断测试方法。我们开发了一种快速（约 3 小时）头孢唑林比色检测法，用于检测氨苄青霉素诱导后上清液中的葡萄球菌β-内酰胺酶（BlaZ）活性。该测试使用从拉丁美洲和美国回收的 689 株血流 MSSA 分离株进行了验证。头孢唑林 MIC 测定的高接种体（10 CFU/ml）用作参考标准（临界值≥16μg/ml）。所有分离株均进行了基因组测序。根据参考标准方法，共有 257（37.3%）株 MSSA 分离株表现出 CzIE。比色检测的总敏感性和特异性分别为 82.5%和 88.9%。携带 A 型 BlaZ（对头孢唑林最有效的酶）的 MSSA 分离株的敏感性为 92.7%，特异性为 87.8%。针对 B 型和 C 型酶的检测性能较低（敏感性分别为 53.3%和 72.3%）。当参考值设定为≥32μg/ml 时，携带 A 型酶的分离株的敏感性为 98.2%。缺乏 BlaZ 的 MSSA 特异性为 100%。根据 CzIE 发表的流行率，在拉丁美洲国家，该测试的总体阴性预测值范围为 81.4%至 95.6%。来自美国的 MSSA 分离株具有遗传多样性，与拉丁美洲 MSSA 之间没有明显的基因组差异，分布在 18 个序列型中。一种新的测试方法可以快速识别大多数表现出 CzIE 的 MSSA 分离株，特别是携带 A 型 BlaZ 的分离株。与使用高接种体的 MIC 测定相比，快速检测法价格低廉、可行且易于实施。经过少量验证步骤后，它可以纳入常规临床实验室工作流程。
