Performance Evaluation of the Gradient Diffusion Strip Method and Disk Diffusion Method for Ceftazidime–Avibactam Against Enterobacterales and Pseudomonas aeruginosa: A Dual-Center Study

Abstract

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 blaKPC, 33 blaNDM, 7 blaIMP, and 2 blaVIM 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.

Comparative Evaluation of Vitek 2 and Etest versus Broth Microdilution for Ceftazidime/Avibactam and Ceftolozane/Tazobactam Susceptibility Testing of Enterobacterales and Pseudomonas aeruginosa

“…According to our findings, the CZA Etest for Enterobacterales isolates yielded a CA, EA, ME and VME of 100%, 97%, 0% and 0%, respectively, which is in agreement with those previously reported when using the EUCAST breakpoint (CA, EA, ME and VME of 100%, 100%, 0% and 0%, respectively) [24]. Earlier observations have also supported the appropriate performance of the Etest for CZA AST against Enterobacterales following the CLSI criteria [25][26][27].…”

“…Additionally, applying the EUCAST breakpoints, previous studies have reported VME rates of 4.5–7.2%, corroborating our results [ 24 , 28 ]. Of note, no VMEs were noted with the CLSI breakpoints [ 25 , 26 ], highlighting the impact of the criteria applied for AST interpretation.…”

Performance of Ceftazidime-Avibactam 30/20-μg and 10/4-μg Disks for Susceptibility Testing of Enterobacterales and Pseudomonas aeruginosa

“…Concerningly, the ceftazidime-avibactam automated susceptibility system is not widely applied in China, and the reference broth microdilution (BMD) method is difficult for routine microbiology laboratories to perform. Although Etest has demonstrated exemplary performance for ceftazidime-avibactam susceptibility testing with Enterobacterales and P. aeruginosa isolates ( 11 – 13 ), it is costly. To sum up, the disk diffusion test is the optimal option in most laboratories, because it is convenient, economical, and practical; however, there are some drawbacks to the disk diffusion test, such as different specifications and manufacturers, subjective measurements, and inoculum effects.…”

Electrokinetics in antimicrobial resistance analysis: A review

“…Results from antimicrobial susceptibility testing (AST) and resistant bacteria identification (ID) are regarded as the definitive data in diagnosis of the infectious diseases. Disk diffusion [5], gradient diffusion [6], antibiotic strips [7], broth microdilution [8], and so on are considered current golden standard methods that are accurate and sensitive. However, these approaches rely on complicated and redundant pre‐analytical processing of the samples [9].…”