Abstract：
OBJECTIVE: To evaluate the performance of the rapid colorimetric polymyxin B microelution (RCPEm) in determining polymyxin B resistance directly from Enterobacterales-positive blood cultures.
METHODS: A set volume of positive blood culture bottles (diluted 1:10) was inoculated into a glucose-broth-phenol red solution (NP solution), where a polymyxin B disk was previously eluted (final concentration of 3 µg/mL). Test was read each 1 h for up to 4 h. Color change from red/orange to yellow indicated resistant isolates. Results were compared to the reference method, broth microdilution (BMD), performed from colonies grown on solid media from the same blood culture bottle.
RESULTS: One hundred fifty-two Enterobacterales-positive blood cultures were evaluated, 22.4% (34/152) of them resistant to polymyxin B (including 6.6% with borderline MICs). When performing directly from positive blood cultures (RCPEm-BC), specificity and sensitivity were 99.1% and 94.1%, respectively. Of note, 79.4% (27/34) of truly resistant isolates required 3 h of incubation, compared to the 18 ± 2 h incubation that microtiter plates of BMD demand before reading can be performed.
CONCLUSIONS: RCPEm directly from blood cultures has great potential to be part of the routine of clinical microbiology laboratories to establish polymyxin B susceptibility, impacting outcome of patients with bloodstream infections caused by carbapenem-resistant Enterobacterales.
METHODS: A set volume of positive blood culture bottles (diluted 1:10) was inoculated into a glucose-broth-phenol red solution (NP solution), where a polymyxin B disk was previously eluted (final concentration of 3 µg/mL). Test was read each 1 h for up to 4 h. Color change from red/orange to yellow indicated resistant isolates. Results were compared to the reference method, broth microdilution (BMD), performed from colonies grown on solid media from the same blood culture bottle.
RESULTS: One hundred fifty-two Enterobacterales-positive blood cultures were evaluated, 22.4% (34/152) of them resistant to polymyxin B (including 6.6% with borderline MICs). When performing directly from positive blood cultures (RCPEm-BC), specificity and sensitivity were 99.1% and 94.1%, respectively. Of note, 79.4% (27/34) of truly resistant isolates required 3 h of incubation, compared to the 18 ± 2 h incubation that microtiter plates of BMD demand before reading can be performed.
CONCLUSIONS: RCPEm directly from blood cultures has great potential to be part of the routine of clinical microbiology laboratories to establish polymyxin B susceptibility, impacting outcome of patients with bloodstream infections caused by carbapenem-resistant Enterobacterales.
摘要：
目的：评估快速比色多粘菌素B微洗脱（RCPEm）直接从肠杆菌阳性血培养物中测定多粘菌素B耐药性的性能。
方法：将一定体积的阳性血培养瓶（1:10稀释）接种到葡萄糖-肉汤-酚红溶液（NP溶液）中，其中先前洗脱了多粘菌素B圆盘（最终浓度为3µg/mL）。每1小时读取测试,直至4小时。从红色/橙色到黄色的颜色变化指示抗性分离株。将结果与参考方法进行比较，肉汤微量稀释（BMD），从来自相同血液培养瓶的固体培养基上生长的菌落进行。
结果：评估了一百五十二例肠杆菌阳性血培养物，其中22.4％（34/152）对多粘菌素B具有抗性（包括6.6％的临界MIC）。当直接从阳性血培养（RCPEm-BC）进行时，特异性和敏感性分别为99.1%和94.1%,分别。值得注意的是，79.4%(27/34)的真正耐药分离株需要3小时的孵育，与18±2小时孵育相比，可以在读取前进行BMD需求的微量滴定板。
结论：直接来自血培养的RCPEm很有可能成为临床微生物学实验室常规建立多粘菌素B易感性的一部分，影响由耐碳青霉烯类肠杆菌引起的血流感染患者的预后。
方法：将一定体积的阳性血培养瓶（1:10稀释）接种到葡萄糖-肉汤-酚红溶液（NP溶液）中，其中先前洗脱了多粘菌素B圆盘（最终浓度为3µg/mL）。每1小时读取测试,直至4小时。从红色/橙色到黄色的颜色变化指示抗性分离株。将结果与参考方法进行比较，肉汤微量稀释（BMD），从来自相同血液培养瓶的固体培养基上生长的菌落进行。
结果：评估了一百五十二例肠杆菌阳性血培养物，其中22.4％（34/152）对多粘菌素B具有抗性（包括6.6％的临界MIC）。当直接从阳性血培养（RCPEm-BC）进行时，特异性和敏感性分别为99.1%和94.1%,分别。值得注意的是，79.4%(27/34)的真正耐药分离株需要3小时的孵育，与18±2小时孵育相比，可以在读取前进行BMD需求的微量滴定板。
结论：直接来自血培养的RCPEm很有可能成为临床微生物学实验室常规建立多粘菌素B易感性的一部分，影响由耐碳青霉烯类肠杆菌引起的血流感染患者的预后。
