Abstract
Abstract
Background:
Ceftazidime-avibactam is ceftazidime combined with the novel non-β-lactam β-lactamase inhibitor avibactam, which inhibits Ambler class A (e.g., extended-spectrum β-lactamase [ESBL] and KPC), class C, and some class D enzymes. We evaluated the activity of ceftazidime-avibactam against aerobic gram negative bacteria causing intra-abdominal infections (IAI).
Methods:
A total of 1,540 isolates were collected, one each from patient, with IAI in 57 United States hospitals in 2012–2014. Susceptibility testing was performed by reference broth microdilution methods, and Enterobacteriaceae isolates with an ESBL phenotype were evaluated by a microarray-based assay for the presence of genes encoding the CTX-M, TEM, SHV, KPC, NDM, and transferable AmpC enzymes.
Results:
All Escherichia coli isolates were susceptible to ceftazidime-avibactam, whereas the susceptibility rates for meropenem, piperacillin-tazobactam, and gentamicin were 99.8%, 93.6%, and 85.5%, respectively. Among Klebsiella pneumoniae isolates, the highest ceftazidime-avibactam minimum inhibitory concentration (MIC) value was only 2 mcg/mL (MIC50/90 0.12/0.25 mcg/mL; 100% susceptible), whereas susceptibility rates to meropenem and gentamicin were 94.5% and 91.9%, respectively. The ESBL-phenotype rates among E. coli and K. pneumoniae were 15.8% and 13.3%, respectively. Overall, only one Enterobacteriaceae isolate (Enterobacter cloacae) was not susceptible to ceftazidime-avibactam and had negative results for all β-lactamases tested. Against Pseudomonas aeruginosa, ceftazidime-avibactam (MIC50/90 2/4 mcg/mL; 97.1% susceptible) and amikacin (MIC50/90 2/8 mcg/mL; 99.0% susceptible) were the most active compounds, and ceftazidime-avibactam retained activity against many meropenem-non-susceptible (88.6% susceptible) and piperacillin-tazobactam-non-susceptible (82.9% susceptible) strains.
Conclusion:
Ceftazidime-avibactam coverage (98.7% inhibited at ≤8 mcg/mL) of intra-abdominal infection pathogens was greater than that observed for meropenem (95.7% susceptible) and piperacillin-tazobactam (88.4% susceptible).
I
Avibactam is a novel broad-spectrum non-β-lactam β-lactamase inhibitor with activity against common serine β-lactamase enzymes, including Ambler class A (e.g., ESBL and KPC), class C (AmpC), and some class D (OXA-48) enzymes [5,6]. The addition of avibactam to ceftazidime restores activity against common gram negative pathogens causing IAI, including most of those that are resistant to carbapenem agents (e.g., meropenem) as a result of the production of β-lactamase enzymes [2]. Ceftazidime-avibactam was approved recently by the U.S. Food and Drug Administration (FDA) for the treatment of complicated IAIs, in combination with metronidazole, as well as complicated urinary tract infections (UTIs), including pyelonephritis, in patients with limited or no alternative treatment options [7]. Two Phase 3 clinical trials were completed recently (data available through http://clinicaltrials.gov). Trial NCT01726023 compared ceftazidime-avibactam plus metronidazole with meropenem for the treatment of complicated IAI, and NCT01644643 compared ceftazidime-avibactam and best available therapy for the treatment of complicated UTI caused by ceftazidime-resistant gram negative organisms. Ceftazidime-avibactam also is under clinical development for the treatment of nosocomial pneumonia (NCT01808092). We evaluated the activity of ceftazidime-avibactam against contemporary (2012–2014) isolates causing IAI in U.S. medical centers.
Materials and Methods
Bacterial isolates
A total of 1,540 gram negative organisms, including 1,312 Enterobacteriaceae, 210 Pseudomonas aeruginosa, and 18 Acinetobacter spp., were collected at 57 U.S. hospitals from patients with IAI between January 2012 and December 2014 as part of the International Network for Optimal Resistance Monitoring (INFORM) program [8]. Isolates determined to be significant by local criteria as the probable cause of the IAI were collected (one per patient episode), and only aerobic gram negative strains were included in this investigation. Species identification was confirmed when necessary by matrix-assisted laser desorption ionization–time of flight mass spectrometry (MALDI-TOF MS) using the Bruker Daltonics MALDI Biotyper (Billerica, MA) following the manufacturer's instructions.
Antimicrobial susceptibility testing
All isolates were tested for susceptibility using the reference broth microdilution method, as described by the Clinical and Laboratory Standards Institute (CLSI) [9]. Ceftazidime was combined with avibactam at a fixed concentration of 4 mcg/mL. Ceftazidime-avibactam breakpoints approved by the FDA (≤8 mcg/mL for susceptible and ≥16 mcg/mL for resistant) were applied for all Enterobacteriaceae species and P. aeruginosa [7]. Susceptibility interpretations for comparator agents were those found in CLSI document M100-S26 [10], European Society of Clinical Microbiology and Infectious Diseases (EUCAST) [11] breakpoints, or the FDA-approved package insert [12]. Quality control (QC) was performed using Escherichia coli ATCC 25922 and 35218, Klebsiella pneumoniae 700603, and P. aeruginosa ATCC 27853. All quality control MIC results were within acceptable ranges, as published in CLSI documents [10].
Screening for β-lactamases
Isolates displaying an ESBL phenotype (MIC >1 mcg/mL for aztreonam, ceftazidime, or ceftriaxone [10]) were tested for β-lactamase-encoding genes using a microarray-based assay (Check-MDR CT101 kit; Check-points; Wageningen, The Netherlands). The assay was performed according to the manufacturer's instructions. This kit has the capability to detect CTX-M groups 1, 2, 8 + 25, and 9; TEM wild-type (WT) and ESBL; SHV WT and ESBL; ACC; ACT/MIR; CMYII; DHA; FOX; KPC; and NDM-1. The most common mutations that expand the spectrum of TEM and SHV enzymes are detected by this assay, and these mutations include 104K, 164S/C/H, and 123S for TEM and 138S, 238A, and 240K for SHV. Validation of the assay against U.S. isolates was performed previously [13]. Additionally, all isolates displaying a ceftazidime-avibactam MIC of >4 mcg/mL were screened for the presence of the metallo-β-lactamase- and serine-carbapenemase-encoding gene families (blaIMP, blaVIM, blaNDM, blaKPC, blaOXA-48, blaGES, blaIMI, blaNMC-A, and blaSME) by polymerase chain reaction as previously described [14]. Amplicons were sequenced on both strands, and the results were analyzed using the Lasergene software package (DNASTAR, Madison, WI). Amino acid sequences were compared with those available through the Internet at National Center for Biotechnology Information's Basic Local Alignment Search Tool (NCBI/BLAST).
Results
Overall, 99.9% of Enterobacteriaceae isolates (1,311/1,312) were susceptible to ceftazidime-avibactam (MIC50/90 0.12/0.25 mcg/mL; Tables 1 and 2). Only one Enterobacteriaceae isolate was not susceptible to the combination, an E. cloacae isolate from Indianapolis, IN, which had a MIC of 16 mcg/mL and negative results for all β-lactamases tested. Other compounds active against >90% of Enterobacteriaceae isolates were meropenem (MIC50/90 ≤0.06/≤0.06 mcg/mL; 98.3%/98.7% susceptible [CLSI/EUCAST]) and tigecycline (MIC50/90 0.12/0.5 mcg/mL; 99.0%/96.0% susceptible [FDA/EUCAST]). Piperacillin-tazobactam (MIC50/90 2/16 mcg/mL) and gentamicin (MIC50/90 ≤1/8 mcg/mL) were active against 90.0% and 89.9% of Enterobacteriaceae isolates, respectively, according to the CLSI breakpoint criteria (Table 2).
CAZ = ceftazidime; ESBL = extended-spectrum β-lactamase; MEM = meropenem; NS = not susceptible; P/T = piperacillin-tazobactam.
Criteria as published by CLSI [2016] and EUCAST [2016].
Organisms include Citrobacter freundii (45), C. koseri (12), Enterobacter aerogenes (29), Escherichia coli (627), E. cloacae (147), Klebsiella oxytoca (81), K. pneumoniae (271), Morganella morganii (14), Proteus mirabilis (46), P. vulgaris (5), Providencia rettgeri (2), P. stuartii (3), and Serratia marcescens (30).
Breakpoints from package insert [7].
Breakpoints from package insert [12].
Escherichia coli was the most common organism recovered (40.7%) and had an ESBL-phenotype rate of 15.8% (99/627). All E. coli isolates were susceptible to ceftazidime-avibactam (MIC50/90 0.06/0.12 mcg/mL; Table 1). The organism exhibited high susceptibility rates to tigecycline (MIC50/90 0.06/0.12 mcg/mL; 100% susceptible), meropenem (MIC50/90 ≤0.06/≤0.06 mcg/mL; 99.8% susceptible), and piperacillin-tazobactam (MIC50/90 2/8 mcg/mL; 93.6% susceptible) but reduced susceptibility to gentamicin (MIC50/90 ≤1/>8 mcg/mL; 85.5% susceptible) and levofloxacin (MIC50/90 ≤0.12/>4 mcg/mL; 72.4% susceptible; data not shown).
All Klebsiella spp. isolates were susceptible to ceftazidime-avibactam (MIC50/90 0.12/0.25 mcg/mL), including isolates with an ESBL phenotype (MIC50/90 0.25/1 mcg/mL) and those not susceptible to meropenem (MIC50/90 0.5/2 mcg/mL; Table 1). Klebsiella pneumoniae was the second most common pathogen (17.6% of all aerobic gram negative organisms) and exhibited CLSI susceptibility rates of 94.5% to meropenem (MIC50/90 ≤0.06/≤0.06 mcg/mL), 91.9% to gentamicin (MIC50/90 ≤1/2 mcg/mL), and 88.9% to piperacillin-tazobactam (MIC50/90 4/32 mcg/mL; data not shown). The ESBL-phenotype rates were 13.3% (36/271) among K. pneumoniae and 12.3% (10/81) among K. oxytoca.
Ceftazidime-avibactam activity against ESBL-phenotype E. coli (n = 99) and K. pneumoniae (n = 36) strains stratified by β-lactamase production is presented in Table 3. The most common ESBL observed among E. coli was CTX-M-15: 43 strains [43.4%], including five strains with CTX-M-15 plus CMY-2) and CTX-M-14 (25 strains [25.3%], including one strain with CTX-M-14 plus CMY-2. The highest ceftazidime-avibactam MIC value among CTX-M-14/15-producing strains was 1 mcg/mL (MIC50/90 0.12/0.5 mcg/mL). Among K. pneumoniae, KPC-like was the most common β-lactamase (13 of 36 strains; 36.1%), and the highest ceftazidime-avibactam MIC value was 2 mcg/mL (MIC50/90 0.5/2 mcg/mL; Table 3)
Includes SHV-like (3), FOX-like (1), CMY-2 + CTX-M-15 (5), CMY-2 + CTX-M-14 (1), and CMY-2 + TEM-ESBL (1).
An SHV-like ESBL producer.
Negative results by checkpoints for the following genes: CTX-M Groups 1, 2, 8 + 25 and 9; TEM ESBL; SHV ESBL; ACC; ACT/MIR; CMYII, DHA;FOX, KPC; and NDM-1.
Ceftazidime-avibactam was active against nearly all E. cloacae (MIC50/90 0.12/0.5 mcg/mL; 99.3% susceptible), including ceftazidime-non-susceptible strains (MIC50/90 0.5/1 mcg/mL; 97.8% susceptible; see Table 1). Meropenem (MIC50/90 ≤0.06/0.12 mcg/mL; 98.0%/98.6% susceptible [CLSI/EUCAST]), tigecycline (MIC50/90 0.25/1 mcg/mL; 98.6%/93.2% susceptible [CLSI/EUCAST]), and gentamicin (MIC50/90 ≤1/≤1 mcg/mL; 95.9%/95.9% susceptible [CLSI/EUCAST]) also were active against E. cloacae; whereas only 68.7/66.0 and 78.8%/71.2% of isolates were susceptible (CLSI/EUCAST) to ceftazidime and piperacillin-tazobactam, respectively (data not shown). Among other Enterobacteriaceae species tested, the ceftazidime-avibactam MIC50 ranged from 0.03 to 0.25 mcg/mL, and the MIC90 ranged from 0.06 to 0.5 mcg/mL (Table 1).
Pseudomonas aeruginosa was the third most common pathogen (13.6% of the total), and 97.1% of isolates were susceptible to ceftazidime-avibactam (MIC50/90 2/4 mcg/mL; Tables 1 and 2). Furthermore, ceftazidime-avibactam showed activity against many P. aeruginosa isolates not susceptible to meropenem (88.6% susceptible), piperacillin/tazobactam (82.9% susceptible), or ceftazidime (80.6% susceptible) with a MIC50/90 of 4/16 mcg/mL for all three subsets (Table 1). Amikacin (MIC50/90 2/8 mcg/mL; 99.0%/97.6% susceptible [CLSI/EUCAST]) also was active against P. aeruginosa, whereas susceptibility rates for ceftazidime, meropenem, and piperacillin-tazobactam were 85.2%, 83.3%, and 83.3% (CLSI and EUCAST), respectively (see Table 2). All antimicrobial agents tested exhibited limited activity against Acinetobacter spp. (Table 2).
Among the entire collection of aerobic gram negative organisms evaluated in this investigation, 98.7% of isolates (1,520/1,540) were inhibited at ceftazidime-avibactam MIC of ≤8 mcg/mL, whereas 86.2% (1,327) were susceptible to ceftazidime, 95.7% (1,474) to meropenem, and 88.4% (1,361) to piperacillin-tazobactam (data not shown).
Discussion
The choice of initial antimicrobial therapy for patients with IAI usually is empiric, and failure to initiate an appropriate antimicrobial regimen early in the course of treatment can lead to a greater risk of clinical failure and greater healthcare costs [15]. Whereas broad-spectrum regimens might be more effective, their benefits should be weighed against their greater cost and the potentially greater risk of the development of antimicrobial resistance. There has been a wealth of evidence, however, that proper initial antimicrobial coverage in patients with severe infections, such as complicated IAI and sepsis, has a significant impact in the clinical outcome, the need for re-operation, length of hospitalization, selection of resistant strains, and overall healthcare costs [3,4,15–17].
The guidelines for the treatment of IAI published by the Surgical Infection Society and Infectious Diseases Society of America (IDSA) is a comprehensive document that was prepared by a panel of renowned experts and provides evidence-based recommendations for the diagnosis and subsequent management of pediatric and adult patients with complicated and uncomplicated IAI [1]. Although this document provides excellent treatment guidance, antimicrobial resistance has evolved since its release, and new drugs have been approved for the treatment of IAI since the publication of the last update in 2010 [1]. Ceftazidime-avibactam in combination with metronidazole was approved by the FDA in early 2015 for the treatment of complicated IAI and represents a valuable addition to the armamentarium of antimicrobial agents for this indication [5,7,18].
In the present study, we evaluated a large collection (1,540) of aerobic gram negative organisms isolated from patients hospitalized with IAI in U.S. medical centers between January 2012 and December 2014. Ceftazidime-avibactam was active (MIC ≤8 mcg/mL) against 98.7% of the organisms isolated. The addition of avibactam increased the coverage from 86.2% for ceftazidime alone to 98.7% for the combination. Furthermore, ceftazidime-avibactam coverage against this collection of aerobic gram negative organisms was greater than that observed for meropenem (95.7% susceptible) and piperacillin-tazobactam (88.4% susceptible). Furthermore, ceftazidime-avibactam demonstrated potent activity against Enterobacteriaceae producing ESBLs or KPC-like carbapenemases and inhibited the majority of P. aeruginosa strains not susceptible to ceftazidime or meropenem.
The limitations of the study should be considered when interpreting the data, and it is important to note that the study was not designed to evaluate the prevalence of organisms causing IAI in U.S. hospitals. Although unique isolates were collected consecutively, only aerobic gram negative species were included in this investigation. Another limitation of the study is related to the criteria used for establishing the clinical relevance of an isolate. Each participating center used local criteria, which might differ among the centers. Despite these limitations, the results presented here provide valuable information on the antimicrobial susceptibility of aerobic gram negative organisms causing IAIs in U.S. hospitals and additionally demonstrated that ceftazidime-avibactam represents a valuable treatment option for IAIs, including those caused by MDR Enterobacteriaceae and P. aeruginosa.
Footnotes
Acknowledgments and Author Disclosure Statement
The authors thank all participants in the International Network for Optimal Resistance Monitoring (INFORM) program for providing bacterial isolates.
This study was supported by Allergan. The company was involved in the design and decision to present these results, and JMI Laboratories received compensation fees for services in relation to preparing the abstract/poster, which was funded by the sponsor. Allergan had no involvement in the collection, analysis, or interpretation of the data.
JMI Laboratories, Inc. has received research and educational grants in 2014–2015 from Achaogen, Actavis, Actelion, American Proficiency Institute (API), AmpliPhi, Anacor, Astellas, AstraZeneca, Basilea, Bayer, BD, Cardeas, Cellceutix, CEM-102 Pharmaceuticals, Cempra, Cerexa, Cidara, Cormedix, Cubist, Debiopharm, Dipexium, Dong Wha, Durata, Enteris, Exela, Forest Research Institute, Furiex, Genentech, GSK, Helperby, ICPD, Janssen, Lannett, Longitude, Medpace, Meiji Seika Kasha, Melinta, Merck, Motif, Nabriva, Novartis, Paratek, Pfizer, Pocared, PTC Therapeutics, Rempex, Roche, Salvat, Scynexis, Seachaid, Shionogi, Tetraphase, The Medicines Co., Theravance, ThermoFisher, VenatoRX, Vertex, Wockhardt, Zavante, and some other corporations. Some JMI employees are advisors/consultants for Allergan, Astellas, Cubist, Pfizer, Cempra, and Theravance. With regard to speakers' bureaus and stock options, there are none to declare.