Activity of ceftazidime-avibactam against multidrug-resistance Enterobacteriaceae expressing combined mechanisms of resistance.

Antimicrobial resistance in Enterobacteriaceae is increasing worldwide and is making treating infections caused by multidrug-resistant Enterobacteriaceae a challenge. The use of β-lactam agents is compromised by microorganisms harboring extended-spectrum β-lactamases (ESBLs) and other mechanisms of resistance. Avibactam is a non β-lactam agent that inhibits clinically relevant β-lactamases, such as ESBL and AmpC. The ceftazidime-avibactam combination (CAZ-AVI) was recently approved for use in certain complicated infections, and may provide a therapeutic alternative for infections caused by these microorganisms. The in vitro activity of CAZ and CAZ-AVI (AVI at a fixed concentration of 4mg/L) was tested against 250 clinical isolates of Enterobacteriaceae using broth microdilution. EUCAST breakpoint criteria were used for CAZ, and FDA criteria for CAZ-AVI. Clinical isolates included bacteria producing extended-spectrum β-lactamases (ESBLs) and acquired AmpC β-lactamases (AACBLs). Porin loss in Klebsiella pneumoniae was also evaluated. The combination of AVI with CAZ displayed excellent activity against clinical isolates of ESBL-producing Escherichia coli and Klebsiella pneumoniae, rendering all the ceftazidime-resistant isolates susceptible to ceftazidime. CAZ-AVI retained activity against porin-deficient isolates of K. pneumoniae producing ESBLs, AACBLs, or both, although MIC values were higher compared to porin-expressing isolates. CAZ-AVI rendered all the ceftazidime-resistant AACBL-producing Enterobacteriaceae tested susceptible to ceftazidime. CAZ-AVI showed potent in vitro activity against clinical isolates of Enterobacteriaceae producing ESBLs and/or AACBLs, including K. pneumoniae with loss of porins.

López-Hernández I ，Alonso N ，Fernández-Martínez M ，Zamorano L ，Rivera A ，Oliver A ，Conejo MC ，Martínez-Martínez L ，Navarro F ，Pascual A ... -  《-》

Can Ceftazidime-Avibactam and Aztreonam Overcome β-Lactam Resistance Conferred by Metallo-β-Lactamases in Enterobacteriaceae?

Based upon knowledge of the hydrolytic profile of major β-lactamases found in Gram-negative bacteria, we tested the efficacy of the combination of ceftazidime-avibactam (CAZ-AVI) with aztreonam (ATM) against carbapenem-resistant enteric bacteria possessing metallo-β-lactamases (MBLs). Disk diffusion and agar-based antimicrobial susceptibility testing were initially performed to determine the in vitro efficacy of a unique combination of CAZ-AVI and ATM against 21 representative Enterobacteriaceae isolates with a complex molecular background that included blaIMP, blaNDM, blaOXA-48, blaCTX-M, blaAmpC, and combinations thereof. Time-kill assays were conducted, and the in vivo efficacy of this combination was assessed in a murine neutropenic thigh infection model. By disk diffusion assay, all 21 isolates were resistant to CAZ-AVI alone, and 19/21 were resistant to ATM. The in vitro activity of CAZ-AVI in combination with ATM against diverse Enterobacteriaceae possessing MBLs was demonstrated in 17/21 isolates, where the zone of inhibition was ≥21 mm. All isolates demonstrated a reduction in CAZ-AVI agar dilution MICs with the addition of ATM. At 2 h, time-kill assays demonstrated a ≥4-log10-CFU decrease for all groups that had CAZ-AVI with ATM (8 μg/ml) added, compared to the group treated with CAZ-AVI alone. In the murine neutropenic thigh infection model, an almost 4-log10-CFU reduction was noted at 24 h for CAZ-AVI (32 mg/kg every 8 h [q8h]) plus ATM (32 mg/kg q8h) versus CAZ-AVI (32 mg/kg q8h) alone. The data presented herein require us to carefully consider this new therapeutic combination to treat infections caused by MBL-producing Enterobacteriaceae.

Marshall S ，Hujer AM ，Rojas LJ ，Papp-Wallace KM ，Humphries RM ，Spellberg B ，Hujer KM ，Marshall EK ，Rudin SD ，Perez F ，Wilson BM ，Wasserman RB ，Chikowski L ，Paterson DL ，Vila AJ ，van Duin D ，Kreiswirth BN ，Chambers HF ，Fowler VG Jr ，Jacobs MR ，Pulse ME ，Weiss WJ ，Bonomo RA ... -  《-》

Antimicrobial susceptibility testing of Enterobacteriaceae: determination of disk content and Kirby-Bauer breakpoint for ceftazidime/avibactam.

Yang X ，Wang D ，Zhou Q ，Nie F ，Du H ，Pang X ，Fan Y ，Bai T ，Xu Y ... -  《BMC MICROBIOLOGY》

Successive Emergence of Ceftazidime-Avibactam Resistance through Distinct Genomic Adaptations in bla(KPC-2)-Harboring Klebsiella pneumoniae Sequence Type 307 Isolates.

Ceftazidime-avibactam (CAZ-AVI) is a promising novel treatment for infections caused by carbapenem-resistant Enterobacteriaceae (CRE). Despite improved treatment outcomes compared to those achieved with aminoglycoside- and colistin-based regimens, the rapid evolution of CAZ-AVI resistance during treatment has previously been reported in Klebsiella pneumoniae sequence type 258 (ST258) blaKPC-3-harboring isolates. Here, we report the stepwise evolution and isolation of two phenotypically distinct CAZ-AVI-resistant Klebsiella pneumoniae isolates from a patient with pancreatitis. All susceptible (n = 3) and resistant (n = 5) isolates were of the ST307 clonal background, a rapidly emerging clone. Taking advantage of short-read Illumina and long-read Oxford Nanopore sequencing and full-length assembly of the core chromosome and plasmids, we demonstrate that CAZ-AVI resistance first occurred through a 532G → T blaKPC-2 point mutation in blaKPC-2 (D179Y protein substitution) following only 12 days of CAZ-AVI exposure. While subsequent isolates exhibited substantially decreased meropenem (MEM) MICs (≤2 μg/ml), later cultures demonstrated a second CAZ-AVI resistance phenotype with a lower CAZ-AVI MIC (12 μg/ml) but also MEM resistance (MIC > 128 μg/ml). These CAZ-AVI- and MEM-resistant isolates showed evidence of multiple genomic adaptations, mainly through insertions and deletions. This included amplification and transposition of wild-type blaKPC-2 into a novel plasmid, an IS1 insertion upstream of ompK36, and disruption of the rfb gene locus in these isolates. Our findings illustrate the potential of CAZ-AVI resistance to emerge in non-K. pneumoniae ST258 clonal backgrounds and alternative blaKPC variants. These results raise concerns about the strong selective pressures incurred by novel carbapenemase inhibitors, such as avibactam, on isolates previously considered invulnerable to CAZ-AVI resistance. There is an urgent need to further characterize non-KPC-mediated modes of carbapenem resistance and the intrinsic bacterial factors that facilitate the rapid emergence of resistance during treatment.

Giddins MJ ，Macesic N ，Annavajhala MK ，Stump S ，Khan S ，McConville TH ，Mehta M ，Gomez-Simmonds A ，Uhlemann AC ... -  《-》

Activity of Ceftazidime-Avibactam against Extended-Spectrum- and AmpC β-Lactamase-Producing Enterobacteriaceae Collected in the INFORM Global Surveillance Study from 2012 to 2014.

The in vitro activity of ceftazidime-avibactam was evaluated against 34,062 isolates of Enterobacteriaceae from patients with intra-abdominal, urinary tract, skin and soft-tissue, lower respiratory tract, and blood infections collected in the INFORM (International Network For Optimal Resistance Monitoring) global surveillance study (176 medical center laboratories in 39 countries) in 2012 to 2014. Overall, 99.5% of Enterobacteriaceae isolates were susceptible to ceftazidime-avibactam using FDA approved breakpoints (susceptible MIC of ≤8 μg/ml; resistant MIC of ≥16 μg/ml). For individual species of the Enterobacteriaceae, the ceftazidime-avibactam MIC inhibiting ≥90% of isolates (MIC90) ranged from 0.06 μg/ml for Proteus species to 1 μg/ml for Enterobacter spp. and Klebsiella pneumoniae Carbapenem-susceptible isolates of Escherichia coli, K. pneumoniae, Klebsiella oxytoca, and Proteus mirabilis with a confirmed extended-spectrum β-lactamase (ESBL) phenotype, or a ceftazidime MIC of ≥16 μg/ml if the ESBL phenotype was not confirmed by clavulanic acid inhibition, were characterized further to identify the presence of specific ESBL- and plasmid-mediated AmpC β-lactamase genes using a microarray-based assay and additional PCR assays. Ceftazidime-avibactam demonstrated potent activity against molecularly confirmed ESBL-producing (n = 5,354; MIC90, 0.5 μg/ml; 99.9% susceptible), plasmid-mediated AmpC-producing (n = 246; MIC90, 0.5 μg/ml; 100% susceptible), and ESBL- and AmpC-producing (n = 152; MIC90, 1 μg/ml; 100% susceptible) isolates of E. coli, K. pneumoniae, K. oxytoca, and P. mirabilis We conclude that ceftazidime-avibactam demonstrates potent in vitro activity against globally collected clinical isolates of Enterobacteriaceae, including isolates producing ESBLs and AmpC β-lactamases.

Karlowsky JA ，Biedenbach DJ ，Kazmierczak KM ，Stone GG ，Sahm DF ... -  《-》