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

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.

Zhang J ，Li G ，Zhang G ，Kang W ，Duan S ，Wang T ，Li J ，Huangfu Z ，Yang Q ，Xu Y ，Jia W ，Sun H ... -  《Frontiers in Microbiology》

Assessment of Ceftazidime-Avibactam 30/20-μg Disk, Etest versus Broth Microdilution Results When Tested against Enterobacterales Clinical Isolates.

Han R ，Yang X ，Yang Y ，Guo Y ，Yin D ，Ding L ，Wu S ，Zhu D ，Hu F ... -  《Microbiology Spectrum》

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

Han R ，Shen S ，Yin D ，Ding L ，Shi Q ，Yang Y ，Guo Y ，Wu S ，Zhi P ，Zhu D ，Hu F ... -  《Microbiology Spectrum》

In-vitro Susceptibility Testing Methods for Ceftazidime-avibactam against Carbapenem-resistant Enterobacterales: Comparison with Reference Broth Microdilution Method.

β-lactam antibiotics, mainly cephalosporins, and carbapenems, have been the mainstay of treatment for infections caused by Enterobacterales. However, their role in treating clinical infections has become limited because of the increase in resistance. There is a need to have cost-effective and rapid methods for antimicrobial susceptibility testing methods for newer antibiotics like ceftazidime-avibactam against carbapenem-resistant Enterobacterales (CRE), which can be applied in routine clinical microbiology laboratories. With this aim, the present study was conducted to compare the disk diffusion and gradient diffusion, i.e., the E-test method with the reference broth microdilution (BMD) method for in-vitro testing of ceftazidime-avibactam against CRE. A total of 111 CRE isolates from various clinical samples were included. Conventional PCR (Polymerase Chain Reaction) was done for the detection of genes encoding carbapenemases and to see their expression, modified carbapenem inactivation method (mCIM) along with EDTA (Ethylenediaminetetraacetic acid) carbapenem inactivation method (eCIM) was done. 42.3% (47/111) isolates were resistant to ceftazidime-avibactam by the standard broth microdilution method; however, 45.9% (51/111) were resistant by both disk diffusion and E-test. In 5.4% of isolates (similar in both methods), microbroth dilution method results did not match with E-strip and disk diffusion. Very major errors (VME) by both disk diffusion and E-test were found in 2.1% (1/47), and major errors (ME) were found in 7.8% (5/64) isolates (similar isolates in both methods). The overall categorical agreement (CA) rate was 94.6% for both E-test and disk diffusion, and the essential agreement (EA) rate was 90.1% (100/111) for E-test. 98% (109/111) of CRE harbored carbapenemase genes either singly (30.3%) or in combination with others (69.7%). In conclusion, for CRE, E-test and the disk diffusion method for ceftazidimeavibactam depicted an acceptable performance as an alternative to the reference broth microdilution method.

Sharma B ，Sreenivasan P ，Angrup A ，Kaur S ，Rana S ，Kundu J ，Biswal M ，Ray P ... -  《-》

Performance Evaluation of BD Phoenix NMIC-413 Antimicrobial Susceptibility Testing Panel for Imipenem, Meropenem, and Ertapenem Against Clinical Carbapenem-Resistant and Carbapenem-Susceptible Enterobacterales.

Purpose: The infection of carbapenem-resistant Enterobacterales (CRE) has become a major clinical and healthcare problem worldwide. The screening methods of CRE have been extensively developed but still need improving [e.g., tests with accurate and simple minimum inhibitory (MICs)]. In this study, the performance of the BD Phoenix NMIC-413 AST panel was evaluated against clinical CRE and carbapenem-susceptible Enterobacterales (CSE) in China. The panel was first evaluated in the Chinese clinical lab. Methods: Antimicrobial susceptibility testing of 303 clinical Enterobacterales isolates were conducted by broth microdilution (BMD), Phoenix NMIC-413 AST panel, and disk diffusion method for imipenem, ertapenem, and meropenem. Considering BMD is a gold standard, essential agreement (EA), categorical agreement (CA), minor error (MIE), major error (ME), and very major error (VME) were determined according to CLSI guidelines. CA and EA > 90%, ME <3%, and VME <1.5% were considered as acceptable criteria. Polymerase chain reaction and sanger sequencing were performed to determine the β-lactamase genotypes of CRE isolates. Results: Three hundred and three isolates included 195 CREs and 108 CSEs were enrolled according to the BMD-MIC values of three carbapenems. Tested CREs showing 100 bla KPC-2-positive organisms, 31 bla IMP-positive organisms, 28 bla NDM-positive organisms, 5 bla VIM-positive organisms, 2 both bla IMP and bla VIM-positive organisms, 2 bla OXA-48-positive organisms, and 27 isolates without carbapenemase genes. For the Phoenix NMIC-413 method, CA and EA rates >93%, MIE rates <5%, ME rates <1.75%, and VME rates were 0%, across the three drugs. For the disk diffusion method, the CA rates for three drugs were all >93%, while the MIE and ME rates were all <5 and <3%, respectively. VME rate was 3.28% for imipenem, exceeded the cut-off value specified by CLSI M52, 0 and 0.56% for ertapenem and meropenem, separately. Conclusion: Based on the genomic data, the detection of CRE and CSE was more reliable using the BD Phoenix NMIC-413 panel compared to the BMD and disk approaches. Therefore, our study supports the use of BD Phoenix NMIC-413 panel as a suitable alternative to BMD for the detection of carbapenem resistant isolates in a clinical setting.

Zhang J ，Jia P ，Zhu Y ，Zhang G ，Xu Y ，Yang Q ... -  《Frontiers in Medicine》