Al Mamari Azza Mohammed Khalifa, Al Jabri Zaaima, Sami Hiba, Rizvi Syed Gauhar A, Chan Moon Fai, Al Siyabi Turkiya, Al Muharrmi Zakariya, Rizvi Meher
Department of Microbiology and Immunology, College of Medicine and Health Sciences, Sultan Qaboos University, Muscat, Oman.
Department of Microbiology, Jawaharlal Nehru Medical College, AMU, Aligarh 202001, India.
JAC Antimicrob Resist. 2023 Sep 4;5(5):dlad101. doi: 10.1093/jacamr/dlad101. eCollection 2023 Oct.
Phenotypic characterization of the prevalent AmpC β-lactamases in clinical isolates is essential for making informed empirical decisions and critical for strengthening antimicrobial stewardship programmes. This study focused on assessing six assays, two in-house and four commercial phenotypic tests for detection of AmpC, to study the feasibility of making its detection a routine diagnostic microbiology laboratory activity.
A total of 116 non-duplicate Gram-negative bacteria that were resistant to third-generation cephalosporins and amoxicillin/clavulanic acid, and resistant or susceptible to piperacillin/tazobactam and carbapenems, were screened by cefoxitin discs for AmpC. These isolates were subjected to two in-house (AmpC Tris-EDTA and disc approximation) methods and four commercial tests: D69C AmpC Detection Set; D72C ESBL, AmpC & Carbapenemase Detection Set; combination disc test: ESBL + AmpC Screen Disc Kit; and AmpC MIC Test Strip for confirmation of AmpC production. Ten whole-genome-sequenced AmpC-confirmed Gram-negative isolates were used as positive controls and one as a negative control.
The prevalence of AmpC β-lactamases was 16%. was a major carrier of plasmid-mediated AmpC (26.5%), followed by (23.4%). Phenotypically, 61% of AmpCs were detected by Tris-EDTA (accuracy: 73.8%), 76% by disc approximation (accuracy: 89.2%), 75% by the D69C AmpC Detection Set (accuracy: 95.4%), 74% by the D72C AmpC, ESBL & Carbapenemase Detection Set (accuracy: 95.4%), 76% by the combination disc test (accuracy: 95.4%) and 63% by AmpC MIC Test Strip (accuracy: 87.7%). The sensitivity and specificity of D69C were 97.9% and 88.2%, respectively, and 95.9% and 93.8% for the combination disc test, while for the disc approximation test and D72C they were 93.9% and 75%, and 93.9% and 100%, respectively. Screening by cefoxitin screening was less sensitive (75%) and specific (25%). Disc approximation and the combination disc test detect AmpC in Enterobacterales and also and species.
We recommend the in-house disc approximation test and the commercial D69C, as well as the combination disc test, as excellent tools for detection of AmpC. The cefoxitin test overcalls AmpC and cannot be considered a good stand-alone test for AmpC detection.
对临床分离株中普遍存在的AmpC β-内酰胺酶进行表型特征分析，对于做出明智的经验性决策至关重要，且对加强抗菌药物管理计划至关重要。本研究着重评估六种检测方法，其中两种是内部方法，四种是用于检测AmpC的商业表型检测方法，以研究将其检测作为常规诊断微生物学实验室活动的可行性。
总共116株对第三代头孢菌素和阿莫西林/克拉维酸耐药，对哌拉西林/他唑巴坦和碳青霉烯类耐药或敏感的非重复革兰氏阴性菌，通过头孢西丁纸片法筛选AmpC。这些分离株接受了两种内部方法（AmpC Tris-EDTA和纸片逼近法）和四种商业检测：D69C AmpC检测套装；D72C ESBL、AmpC和碳青霉烯酶检测套装；联合纸片试验：ESBL+AmpC筛选纸片试剂盒；以及AmpC MIC试纸条，以确认AmpC的产生。十株经全基因组测序确认产AmpC的革兰氏阴性分离株用作阳性对照，一株用作阴性对照。
AmpC β-内酰胺酶的流行率为16%。大肠埃希菌是质粒介导的AmpC的主要携带者（26.5%），其次是肺炎克雷伯菌（23.4%）。表型上，61%的AmpC通过Tris-EDTA检测到（准确率：73.8%），76%通过纸片逼近法检测到（准确率：89.2%），75%通过D69C AmpC检测套装检测到（准确率：95.4%），74%通过D72C AmpC、ESBL和碳青霉烯酶检测套装检测到（准确率：95.4%），76%通过联合纸片试验检测到（准确率：95.4%），63%通过AmpC MIC试纸条检测到（准确率：87.7%）。D69C的敏感性和特异性分别为97.9%和88.2%，联合纸片试验的敏感性和特异性分别为95.9%和93.8%，而纸片逼近法试验和D72C的敏感性和特异性分别为93.9%和75%，以及93.9%和100%。通过头孢西丁筛选的敏感性（75%）和特异性（25%）较低。纸片逼近法和联合纸片试验可检测肠杆菌科以及肺炎克雷伯菌和大肠埃希菌属中的AmpC。
我们推荐内部纸片逼近法试验和商业D69C以及联合纸片试验，作为检测AmpC的优秀工具。头孢西丁试验对AmpC的判断过度，不能被视为检测AmpC的良好独立试验。
