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In Vitro Activities and Inoculum Effects of Ceftazidime-Avibactam and Aztreonam-Avibactam against Carbapenem-Resistant Enterobacterales Isolates from South Korea.


ABSTRACT: Ceftazidime-avibactam (CAZ-AVI) and aztreonam-avibactam (AZT-AVI) are novel antibiotic combinations active against multidrug-resistant Gram-negative pathogens. This study aimed to evaluate their in vitro activities and inoculum effects in carbapenem-resistant Enterobacterales (CRE), including carbapenemase-producing (CP)-CRE and non-CP-CRE. A total of 81 independent clinical isolates of carbapenem-resistant Escherichia coli and Klebsiella pneumoniae were collected. CAZ-AVI and AZT-AVI minimal inhibitory concentrations (MICs) were evaluated by broth microdilution using standard and high inocula. The inoculum effect was defined as an ?8-fold increase in MIC with high inoculum. Phenotypic determination of ?-lactam resistance mechanism and PCR for carbapenemase genes were performed. Of the 81 CRE isolates, 35 (43%) were CP-CRE. Overall, 73% of the isolates were susceptible to CAZ-AVI, and 95% had low AZT-AVI MICs (?8 µg/mL). The MIC50/MIC90s of CAZ-AVI and AZT-AVI were 4/?512 µg/mL and 0.5/4 µg/mL, respectively. CAZ-AVI was more active against non-CP-CRE than against CP-CRE (susceptibility 80% vs. 63%, p = 0.08; MIC50/MIC90, 2/16 ?g/mL vs. 4/?512 ?g/mL), whereas AZT-AVI was more active against CP-CRE (MIC50/MIC90, 0.25/1 ?g/mL vs. 0.5/8 ?g/mL). All four isolates with high AZT-AVI MIC (?16 ?g/mL) were resistant to CAZ-AVI, but only 18% (4/22) of CAZ-AVI-resistant isolates had high AZT-AVI MIC. The rates of the inoculum effect for CAZ-AVI and AZT-AVI were 18% and 47%, respectively (p < 0.001). Interestingly, the frequency of the AZT-AVI inoculum effect was higher in K. pneumoniae than E. coli (64% vs. 8%, p < 0.001). AZT-AVI is more active against CRE than CAZ-AVI, even in CP-CRE and CAZ-AVI-resistant isolates. The presence of a substantial inoculum effect may contribute to clinical failure in high-inoculum infections treated with AZT-AVI.

SUBMITTER: Kim T 

PROVIDER: S-EPMC7765481 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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In Vitro Activities and Inoculum Effects of Ceftazidime-Avibactam and Aztreonam-Avibactam against Carbapenem-Resistant <i>Enterobacterales</i> Isolates from South Korea.

Kim Taeeun T   Lee Seung Cheol SC   Bae Moonsuk M   Sung Heungsup H   Kim Mi-Na MN   Jung Jiwon J   Kim Min Jae MJ   Kim Sung-Han SH   Lee Sang-Oh SO   Choi Sang-Ho SH   Kim Yang Soo YS   Chong Yong Pil YP  

Antibiotics (Basel, Switzerland) 20201215 12


Ceftazidime-avibactam (CAZ-AVI) and aztreonam-avibactam (AZT-AVI) are novel antibiotic combinations active against multidrug-resistant Gram-negative pathogens. This study aimed to evaluate their in vitro activities and inoculum effects in carbapenem-resistant <i>Enterobacterales</i> (CRE), including carbapenemase-producing (CP)-CRE and non-CP-CRE. A total of 81 independent clinical isolates of carbapenem-resistant <i>Escherichia coli</i> and <i>Klebsiella pneumoniae</i> were collected. CAZ-AVI a  ...[more]

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