Objectives: Ceftazidime–avibactam is a novel synthetic beta-lactam + beta-lactamase inhibitor combination. We evaluated the performance of the gradient diffusion strip method and the disk diffusion method for the determination of ceftazidime–avibactam against Enterobacterales and Pseudomonas aeruginosa.

Methods: Antimicrobial susceptibility testing of 302 clinical Enterobacterales and Pseudomonas aeruginosa isolates from two centers were conducted by broth microdilution (BMD), gradient diffusion strip method, and disk diffusion method for ceftazidime–avibactam. Using BMD as a gold standard, essential agreement (EA), categorical agreement (CA), major error (ME), and very major error (VME) were determined according to CLSI guidelines. CA and EA rate > 90%, ME rate < 3%, and VME rate < 1.5% were considered as acceptable criteria. Polymerase chain reaction and Sanger sequencing were performed to determine the carbapenem resistance genes of all 302 isolates.

Results: A total of 302 strains were enrolled, among which 182 strains were from center 1 and 120 strains were from center 2. A percentage of 18.21% (55/302) of the enrolled isolates were resistant to ceftazidime–avibactam. The CA rates of the gradient diffusion strip method for Enterobacterales and P. aeruginosa were 100% and 98.65% (73/74), respectively, and the EA rates were 97.37% (222/228) and 98.65% (73/74), respectively. The CA rates of the disk diffusion method for Enterobacterales and P. aeruginosa were 100% and 95.95% (71/74), respectively. No VMEs were found by using the gradient diffusion strip method, while the ME rate was 0.40% (1/247). No MEs were found by using the disk diffusion method, but the VME rate was 5.45% (3/55). Therefore, all the parameters of the gradient diffusion strip method were in line with acceptable criteria. For 31 bla_KPC, 33 bla_NDM, 7 bla_IMP, and 2 bla_VIM positive isolates, both CA and EA rates were 100%; no MEs or VMEs were detected by either method. For 15 carbapenemase-non-producing resistant isolates, the CA and EA rates of the gradient diffusion strips method were 100%. Whereas the CA rate of the disk diffusion method was 80.00% (12/15), the VME rate was 20.00% (3/15).

Conclusion: The gradient diffusion strip method can meet the needs of clinical microbiological laboratories for testing the susceptibility of ceftazidime–avibactam drugs. However, the VME rate > 1.5% (5.45%) by the disk diffusion method. By comparison, the performance of the gradient diffusion strip method was better than that of the disk diffusion method.

目标：头孢他啶-阿维巴坦是一种新型合成β-内酰胺+β-内酰胺酶抑制剂组合。我们评估了梯度扩散条法和圆盘扩散法测定头孢他啶-阿维巴坦的性能肠杆菌目 和 铜绿假单胞菌。

方法： 302临床药敏试验 肠杆菌目 和 铜绿假单胞菌通过肉汤微量稀释 (BMD)、梯度扩散条带法和头孢他啶-阿维巴坦的圆盘扩散法对来自两个中心的分离株进行了分析。使用 BMD 作为黄金标准，根据 CLSI 指南确定基本一致性 (EA)、分类一致性 (CA)、主要错误 (ME) 和非常主要错误 (VME)。CA 和 EA 率 > 90%、ME 率 < 3% 和 VME 率 < 1.5% 被认为是可接受的标准。进行聚合酶链反应和Sanger测序以确定所有302个分离株的碳青霉烯类抗性基因。

结果：共纳入302株菌株，其中182株来自中心1，120株来自中心2。18.21%（55/302）的登记分离株对头孢他啶-阿维巴坦耐药。梯度扩散带法的 CA 率肠杆菌目 和 铜绿假单胞菌分别为 100% 和 98.65% (73/74)，EA 率分别为 97.37% (222/228) 和 98.65% (73/74)。圆盘扩散法的 CA 率肠杆菌目 和 铜绿假单胞菌分别为 100% 和 95.95% (71/74)。梯度扩散条带法未发现VME，ME率为0.40%（1/247）。使用磁盘扩散法未发现ME，但VME率为5.45%（3/55）。因此，梯度扩散带法的所有参数均符合可接受的标准。对于 31布拉_KPC, 33 布拉_无损检测, 7 布拉_IMP, 和 2 布拉_虚拟机阳性分离株，CA 和 EA 率均为 100%；两种方法均未检测到 ME 或 VME。对于 15 株不产碳青霉烯酶的耐药菌株，梯度扩散条带法的 CA 和 EA 率为 100%。而磁盘扩散法的 CA 率为 80.00% (12/15)，而 VME 率为 20.00% (3/15)。

结论：梯度扩散条带法可以满足临床微生物实验室检测头孢他啶-阿维巴坦类药物敏感性的需要。然而，磁盘扩散法的 VME 率 > 1.5% (5.45%)。相比之下，梯度扩散条法的性能优于圆盘扩散法。