Brief Report
21 December 2017

Antimicrobial Activities of Aztreonam-Avibactam and Comparator Agents against Contemporary (2016) Clinical Enterobacteriaceae Isolates

ABSTRACT

A total of 10,451 contemporary (2016) Enterobacteriaceae isolates from 84 U.S. medical centers and 116 metallo-β-lactamase- and/or OXA-48-like-producing Enterobacteriaceae isolates from other countries were tested against aztreonam-avibactam and comparators. All U.S. isolates were inhibited at aztreonam-avibactam MICs of ≤8 μg/ml (MIC50, ≤0.03 μg/ml; MIC90, 0.12 μg/ml), including Klebsiella pneumoniae carbapenemase-producing isolates (n = 102; MIC50, 0.25 μg/ml; MIC90, 0.5 μg/ml), multidrug-resistant isolates (n = 876; MIC50, 0.06 μg/ml; MIC90, 0.25 μg/ml), and extensively drug-resistant isolates (n = 111; MIC50, 0.12 μg/ml; MIC90, 0.5 μg/ml). The highest aztreonam-avibactam MIC value among ex-U.S. isolates was 4 μg/ml.

TEXT

Resistance to carbapenems among Enterobacteriaceae is generally mediated by β-lactamase production. Serine β-lactamases, mainly Klebsiella pneumoniae carbapenemase (KPC), are the most common carbapenemases found in the United States and worldwide, whereas metallo-β-lactamases (MBLs) are more common in some geographic regions, such as India, Italy, Turkey, and some Eastern European countries (1, 2).
The approval of ceftazidime-avibactam by the U.S. Food and Drug Administration (FDA) in 2015 represented an important advancement in the treatment of infections caused by carbapenem-resistant Enterobacteriaceae (CRE) (35). Avibactam restores ceftazidime activity against most carbapenemase-producing Enterobacteriaceae; however, avibactam and all other β-lactamase inhibitors currently available for clinical use do not inhibit MBLs (6).
Aztreonam was approved by the FDA in 1986, and it is still the only clinically available member of the monobactam class (7, 8). Aztreonam is stable to hydrolysis by MBLs, a unique feature, compared to other β-lactams; however, it is hydrolyzed by most clinically relevant serine β-lactamases, such as extended-spectrum β-lactamases, AmpC, and KPC. Because Enterobacteriaceae isolates that produce an MBL usually coproduce a serine β-lactamase, aztreonam was combined with avibactam, and this novel β-lactamase-inhibitor combination is under clinical development (ClinicalTrials registration no. NCT01689207). In this investigation, we assessed the in vitro activity of aztreonam-avibactam against a large collection of contemporary (2016) clinical Enterobacteriaceae isolates recovered from patients hospitalized in U.S. medical centers, as well as selected carbapenemase (NDM-like and OXA-48-like)-producing Enterobacteriaceae isolates recovered outside the United States.
A total of 10,451 Enterobacteriaceae isolates were consecutively collected from 84 medical centers in 37 states, from all 9 U.S. Census divisions, in 2016. These isolates were collected from patients with urinary tract infections (n = 4,222 [40.4%]), pneumonia (n = 2,051 [19.6%]), skin and skin structure infections (n = 1,806 [17.3%]), bloodstream infections (n = 1,641 [15.7%]), intra-abdominal infections (n = 398 [3.8%]), and other infection types (n = 333 [3.2%]), according to defined protocols. Only isolates determined to be significant by local criteria as the reported probable cause of infection were included in the program. Species identification was confirmed by using standard biochemical tests and by using a MALDI Biotyper (Bruker Daltonics, Billerica, MA, USA), according to the manufacturer's instructions, when necessary.
Isolates were categorized as multidrug-resistant (MDR), extensively drug-resistant (XDR), or pan-drug-resistant (PDR) strains according to criteria published by Magiorakos et al. (9), which define MDR strains as being nonsusceptible to ≥1 agent in ≥3 antimicrobial classes, XDR strains as being nonsusceptible to ≥1 agent in all but ≤2 antimicrobial classes, and PDR strains as being nonsusceptible to all antimicrobial classes tested. Isolates were categorized as nonsusceptible based on the CLSI criteria (10), unless noted, and the antimicrobial classes and drug representatives used in the analysis were broad-spectrum cephalosporins (ceftriaxone, ceftazidime, and cefepime), carbapenems (imipenem, meropenem, and doripenem), broad-spectrum penicillin combined with a β-lactamase inhibitor (piperacillin-tazobactam), fluoroquinolones (ciprofloxacin and levofloxacin), aminoglycosides (gentamicin, tobramycin, and amikacin), glycylcyclines (tigecycline [FDA criteria]), and the polymyxins (colistin [EUCAST criteria]). Additionally, CRE was defined as resistant (MIC, ≥4 μg/ml [CLSI criteria]) to imipenem (imipenem was not applied to Proteus mirabilis or indole-positive Proteeae), meropenem, or doripenem.
With the purpose of assessing the in vitro activity of aztreonam-avibactam against Enterobacteriaceae strains producing MBLs or OXA-48-like enzymes, which are very uncommon in the United States, we included a collection of contemporary clinical Enterobacteriaceae isolates that produced these enzymes. The collection contained 116 Enterobacteriaceae isolates, including 59 producing MBLs and 57 producing OXA-48-like enzymes, that were collected in 2016 from 27 medical centers in 19 countries other than the United States. The isolates were from the following countries: Australia (2 isolates), Belarus (6 isolates), Belgium (3 isolates), Brazil (2 isolates), Germany (8 isolates), Greece (3 isolates), Guatemala (1 isolate), Italy (4 isolates), Malaysia (4 isolates), Mexico (5 isolates), Philippines (9 isolates), Russia (23 isolates), Slovakia (1 isolate), Spain (8 isolates), Taiwan (2 isolates), Thailand (5 isolates), Turkey (26 isolates), United Kingdom (2 isolates), and Venezuela (2 isolates).
Isolates were tested against aztreonam-avibactam and all comparator agents with the broth microdilution method, according to CLSI guidelines (11). All tests were conducted in a central monitoring laboratory (JMI Laboratories, North Liberty, IA, USA), and aztreonam-avibactam was tested with avibactam at a fixed concentration of 4 μg/ml. Concurrent quality control (QC) testing was performed to ensure proper test conditions and procedures. QC strains included Escherichia coli ATCC 25922 and ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. All QC results were within published ranges. CLSI (10), EUCAST (12), and FDA (13) susceptibility interpretive criteria were used to determine susceptibility/resistance rates for comparator agents.
Total genomic DNA was extracted using the fully automated Thermo Scientific KingFisher Flex magnetic particle processor (Cleveland, OH, USA). DNA extracts were quantified using the Qubit high-sensitivity double-stranded DNA assay (Invitrogen, Thermo Fisher) and normalized to 0.2 ng/μl. A total of 1 ng high-quality genomic DNA was used as input material for library construction using the Nextera XT DNA library preparation kit (Illumina, San Diego, CA, USA). Libraries were normalized using the bead-based normalization procedure (Illumina) and sequenced with a MiSeq system. Fastq files generated were assembled using the SPAdes assembler and subjected to proprietary software (JMI Laboratories) for screening of β-lactamase genes.
The highest aztreonam-avibactam MIC value observed was 8 μg/ml, which was observed in only 1 isolate (Escherichia coli). Overall, 99.9% of Enterobacteriaceae isolates from the United States were inhibited at aztreonam-avibactam concentrations of ≤1 μg/ml (Table 1).
TABLE 1
TABLE 1 Antimicrobial activity of aztreonam-avibactam tested against the main organisms and organism groups of isolates from U.S. hospitals
Organism and groupaNo. of isolates (cumulative %)MIC50 (μg/ml)MIC90 (μg/ml)
MIC of ≤0.03 μg/mlMIC of 0.06 μg/mlMIC of 0.12 μg/mlMIC of 0.25 μg/mlMIC of 0.5 μg/mlMIC of 1 μg/mlMIC of 2 μg/mlMIC of 4 μg/mlMIC of 8 μg/ml
Enterobacteriaceae (n = 10,451)6,486 (62.1)2,378 (84.8)1,023 (94.6)333 (97.8)152 (99.2)64 (99.9)10 (>99.9)4 (>99.9)1 (100.0)≤0.030.12
    CRE (n = 120)23 (19.2)11 (28.3)35 (57.5)28 (80.8)14 (92.5)6 (97.5)1 (98.3)2 (100.0) 0.120.5
    MDR (n = 876)408 (46.6)157 (64.5)133 (79.7)92 (90.2)48 (95.7)26 (98.6)7 (99.4)4 (99.9)1 (100.0)0.060.25
    XDR (n = 111)28 (25.2)8 (32.4)27 (56.8)27 (81.1)14 (93.7)5 (98.2)2 (100.0)  0.120.5
    PDR (n = 2)1 (50.0)0 (50.0)1 (100.0)      ≤0.03 
Escherichia coli (n = 3,748)2,364 (63.1)1,063 (91.4)263 (98.5)39 (99.5)9 (99.7)4 (99.8)3 (99.9)2 (>99.9)1 (100.0)≤0.030.06
    Ceftriaxone-nonsusceptible (MIC of ≥2 μg/ml) (n = 549)237 (43.2)193 (78.3)83 (93.4)18 (96.7)8 (98.2)4 (98.9)3 (99.5)2 (99.8)1 (100.0)0.060.12
Klebsiella pneumoniae (n = 2,200)1,487 (67.6)435 (87.4)206 (96.7)59 (99.4)7 (99.7)4 (99.9)2 (100.0)  ≤0.030.12
    Ceftriaxone-nonsusceptible (MIC of ≥2 μg/ml) (n = 281)126 (44.8)53 (63.7)56 (83.6)37 (96.8)5 (98.6)3 (99.6)1 (100.0)  0.060.25
    Meropenem-nonsusceptible (MIC of ≥2 μg/ml) (n = 76)14 (18.4)6 (26.3)26 (60.5)23 (90.8)5 (97.4)1 (98.7)1 (100.0)  0.120.25
    Colistin-nonsusceptible (MIC of ≥4 μg/ml) (n = 58)21 (36.2)11 (55.2)11 (74.1)11 (93.1)3 (98.3)1 (100.0)   0.060.25
Klebsiella oxytoca (n = 480)299 (62.3)112 (85.6)56 (97.3)11 (99.6)2 (100.0)    ≤0.030.12
Proteus mirabilis (n = 825)815 (98.8)7 (99.6)2 (99.9)1 (100.0)     ≤0.03≤0.03
Enterobacter cloacae (n = 1,021)335 (32.8)316 (63.8)151 (78.6)97 (88.1)79 (95.8)41 (99.8)1 (99.9)1 (100.0) 0.060.5
    Ceftazidime-nonsusceptible (MIC of ≥8 μg/ml) (n = 263)15 (5.7)20 (13.3)36 (27.0)76 (55.9)73 (83.7)41 (99.2)1 (99.6)1 (100.0) 0.251
Enterobacter aerogenes (n = 427)220 (51.5)114 (78.2)61 (92.5)19 (97.0)10 (99.3)2 (99.8)0 (99.8)1 (100.0) ≤0.030.12
Morganella morganii (n = 341)291 (85.3)21 (91.5)15 (95.9)8 (98.2)4 (99.4)1 (99.7)1 (100.0)  ≤0.030.06
Citrobacter koseri (n = 214)177 (82.7)28 (95.8)7 (99.1)2 (100.0)     ≤0.030.06
Citrobacter freundii (n = 318)119 (37.4)102 (69.5)49 (84.9)26 (93.1)18 (98.7)3 (99.7)1 (100.0)  0.060.25
Serratia marcescens (n = 436)11 (2.5)146 (36.0)192 (80.0)61 (94.0)17 (97.9)7 (99.5)2 (100.0)  0.120.25
Proteus vulgaris (n = 4)4 (100.0)        ≤0.03 
Providencia spp. (n = 223)212 (95.1)6 (97.8)3 (99.1)1 (99.6)1 (100.0)    ≤0.03≤0.03
a
CRE, carbapenem-resistant Enterobacteriaceae; MDR, multidrug-resistant; XDR, extensively drug-resistant; PDR, pan-drug-resistant.
Aztreonam-avibactam was highly active against CRE (n = 120; MIC50, 0.12 μg/ml; MIC90, 0.5 μg/ml; highest MIC, 4 μg/ml), MDR strains (n = 876; MIC50, 0.06 μg/ml; MIC90, 0.25 μg/ml; highest MIC, 8 μg/ml), XDR strains (n = 111; MIC50, 0.12 μg/ml; MIC90, 0.5 μg/ml; highest MIC, 4 μg/ml), and PDR strains (2 isolates with aztreonam-avibactam MIC values of ≤0.03 and 0.12 μg/ml) (Tables 1 and 2). Other resistant subsets evaluated included ceftriaxone-nonsusceptible E. coli (n = 549; MIC50, 0.06 μg/ml; MIC90, 0.12 μg/ml), ceftriaxone-nonsusceptible Klebsiella pneumoniae (n = 281; MIC50, 0.06 μg/ml; MIC90, 0.25 μg/ml), meropenem-nonsusceptible K. pneumoniae (n = 76; MIC50, 0.12 μg/ml; MIC90, 0.25 μg/ml), colistin-nonsusceptible K. pneumoniae (n = 58; MIC50, 0.06 μg/ml; MIC90, 0.25 μg/ml; highest MIC, 1 μg/ml), and ceftazidime-nonsusceptible Enterobacter cloacae (n = 263; MIC50, 0.25 μg/ml; MIC90, 1 μg/ml) (Table 1). Aztreonam-avibactam was active against all individual Enterobacteriaceae species and genera, with MIC50 values ranging from ≤0.03 μg/ml (E. coli, K. pneumoniae, Klebsiella oxytoca, Enterobacter aerogenes, Morganella morganii, Citrobacter koseri, Proteus mirabilis, Proteus vulgaris, and Providencia spp.) to 0.12 μg/ml (Serratia marcescens) and MIC90 values ranging from ≤0.03 μg/ml (P. mirabilis and Providencia spp.) to 0.5 μg/ml (E. cloacae) (Table 1).
TABLE 2
TABLE 2 Activity of aztreonam-avibactam and comparator antimicrobial agents when tested against isolates from U.S. hospitals (2016)
Organism and antimicrobial agentaMIC50 (μg/ml)MIC90 (μg/ml)CLSI criteriabEUCAST criteriab
Susceptible (%)Resistant (%)Susceptible (%)Resistant (%)
All Enterobacteriaceae (n = 10,451)      
    Aztreonam-avibactam≤0.030.12NAcNANANA
    Aztreonam0.061687.810.985.812.2
    Ceftriaxone≤0.06>884.414.684.414.6
    Ceftazidime0.251687.910.785.012.1
    Cefepime≤0.12290.97.089.47.9
    Ampicillin-sulbactam16>3249.434.449.450.6
    Piperacillin-tazobactam21692.53.989.27.5
    Meropenem0.030.0698.81.099.00.5
    Imipenem≤0.12190.62.597.50.5
    Ciprofloxacin≤0.03>481.616.978.019.9
    Levofloxacin0.06>483.114.879.218.2
    Gentamicin0.5291.57.490.88.5
    Amikacin2499.40.298.40.6
    Tigecycline0.25196.80.1d90.53.2
    Colistin0.25>8  79.120.9
CRE (n = 120)e      
    Aztreonam-avibactam0.120.5NANANANA
    Aztreonam>16>162.597.51.797.5
    Ceftriaxone>8>81.797.51.797.5
    Ceftazidime>32>324.290.82.595.8
    Cefepime>16>168.380.02.587.5
    Ampicillin-sulbactam>32>320.899.20.899.2
    Piperacillin-tazobactam>64>643.389.23.396.7
    Meropenem8>324.287.512.546.7
    Imipenem8>84.294.25.844.2
    Ciprofloxacin>4>417.570.815.082.5
    Levofloxacin>4>426.766.715.880.0
    Gentamicin8>843.334.240.856.7
    Amikacin83274.26.759.225.8
    Tigecycline0.5296.70.0d85.03.3
    Colistin0.25>8  81.718.3
MDR (n = 876)f      
    Aztreonam-avibactam0.060.25NANANANA
    Aztreonam>16>1634.162.628.965.9
    Ceftriaxone>8>823.474.223.474.2
    Ceftazidime16>3231.762.424.268.3
    Cefepime16>1638.451.032.955.3
    Ampicillin-sulbactam>32>3212.778.912.787.3
    Piperacillin-tazobactam16>6456.825.648.843.2
    Meropenem0.06486.211.888.26.2
    Imipenem0.5468.216.283.85.8
    Ciprofloxacin>4>411.977.79.189.6
    Levofloxacin>4>421.868.412.282.9
    Gentamicin8>840.049.435.660.0
    Amikacin41693.41.786.56.6
    Tigecycline0.5482.40.3d69.717.6
    Colistin0.25>8  58.341.7
XDR (n = 111)g      
    Aztreonam-avibactam0.120.5NANANANA
    Aztreonam>16>1616.282.910.883.8
    Ceftriaxone>8>84.593.74.593.7
    Ceftazidime>32>329.085.64.591.0
    Cefepime>16>1612.679.39.983.8
    Ampicillin-sulbactam>32>320.993.70.999.1
    Piperacillin-tazobactam>64>6413.578.412.686.5
    Meropenem8>3230.664.036.041.4
    Imipenem8>819.869.430.638.7
    Ciprofloxacin>4>40.086.50.0100.0
    Levofloxacin>4>49.980.20.997.3
    Gentamicin>8>818.951.418.081.1
    Amikacin8>3265.811.755.034.2
    Tigecycline1479.30.0d64.920.7
    Colistin0.25>8  57.742.3
a
CRE, carbapenem-resistant Enterobacteriaceae; MDR, multidrug-resistant; XDR, extensively drug-resistant.
b
Criteria published by the CLSI (10) and EUCAST (12).
c
NA, not applicable; breakpoints for aztreonam-avibactam have not been defined.
d
Breakpoints from the tigecycline package insert (13).
e
Organisms include Citrobacter freundii species complex (4 isolates), Enterobacter aerogenes (5 isolates), Enterobacter cloacae species complex (15 isolates), Escherichia coli (5 isolates), Klebsiella oxytoca (7 isolates), Klebsiella pneumoniae (74 isolates), Proteus mirabilis (2 isolates), Providencia stuartii (1 isolate), Raoultella ornithinolytica (1 isolate), Serratia marcescens (4 isolates), and Raoultella strains not identified to the species level (2 isolates).
f
Organisms include Citrobacter freundii species complex (20 isolates), Citrobacter koseri (1 isolate), Enterobacter aerogenes (11 isolates), Enterobacter cloacae species complex (75 isolates), Escherichia coli (242 isolates), Hafnia alvei (3 isolates), Klebsiella oxytoca (22 isolates), Klebsiella pneumoniae (194 isolates), Morganella morganii (51 isolates), Proteus mirabilis (158 isolates), Proteus vulgaris group (1 isolate), Providencia rettgeri (5 isolates), Providencia stuartii (58 isolates), Raoultella ornithinolytica (1 isolate), Serratia liquefaciens (1 isolate), S. marcescens (30 isolates), Raoultella strains not identified to the species level (2 isolates), and Serratia strain not identified to the species level (1 isolate).
g
Organisms include Citrobacter freundii species complex (4 isolates), Enterobacter cloacae species complex (14 isolates), Escherichia coli (1 isolate), Klebsiella oxytoca (3 isolates), Klebsiella pneumoniae (60 isolates), Morganella morganii (6 isolates), Proteus mirabilis (9 isolates), Providencia stuartii (8 isolates), Raoultella ornithinolytica (1 isolate), Serratia marcescens (4 isolates), and Raoultella strain not identified to the species level (1 isolate).
Amikacin (MIC50, 2 μg/ml; MIC90, 4 μg/ml [99.4% susceptible per CLSI criteria]), meropenem (MIC50, 0.03 μg/ml; MIC90, 0.06 μg/ml [98.8% susceptible per CLSI criteria]), and tigecycline (MIC50, 0.25 μg/ml; MIC90, 1 μg/ml [96.8% susceptible per FDA criteria and 90.5% susceptible per EUCAST criteria]) were also very active against the entire Enterobacteriaceae collection, but these antimicrobial agents exhibited limited activity against CRE, MDR, and/or XDR isolates (Table 2). The most active compound tested against MDR and XDR Enterobacteriaceae isolates was aztreonam-avibactam (99.9% and 100.0% of isolates, respectively, were inhibited at ≤4 μg/ml), followed by amikacin (93.4% and 65.8% susceptible, respectively, per CLSI criteria and 86.5% and 55.0% susceptible per EUCAST criteria), meropenem (86.2% and 30.6% susceptible, respectively, per CLSI criteria and 88.2% and 36.0% susceptible per EUCAST criteria), and tigecycline (82.4% and 79.3% susceptible, respectively, per CLSI criteria and 69.7% and 64.9% susceptible per EUCAST criteria) (Table 2). Among CRE isolates, 100.0% were susceptible to aztreonam-avibactam at ≤4 μg/ml (the CLSI susceptibility breakpoint for aztreonam) (MIC50, 0.12 μg/ml; MIC90, 0.5 μg/ml), 96.7% (FDA criteria) and 85.0% (EUCAST criteria) of isolates were susceptible to tigecycline, and 74.2% (CLSI criteria) and 59.2% (EUCAST criteria) of isolates were susceptible to amikacin. Furthermore, only 81.7% of CRE isolates, 58.3% of MDR isolates, and 57.7% of XDR isolates were susceptible to colistin according to EUCAST criteria (≤2 μg/ml) (Table 2).
Among 120 CRE isolates found in the United States, a total of 106 carbapenemases were detected in 106 isolates, including 102 KPCs (35 KPC-2, 66 KPC-3, and 1 KPC-4), 2 SME-4, 1 NDM-1, and 1 IMP-27 (see Table S1 in the supplemental material). The carbapenemases produced by the 116 strains isolated in other countries (ex-U.S. isolates) included IMP-4 (2 isolates), NDM-1 (40 isolates), NDM-5 (2 isolates), NDM-6 (1 isolate), NDM-7 (7 isolates), VIM-1 (7 isolates), OXA-48 (56 isolates), OXA-244 (1 isolate), and OXA-370 (1 isolate). One K. pneumoniae isolate produced NDM-1 and OXA-48 (Table S2).
Aztreonam-avibactam was highly active against KPC-producing strains, with an MIC50 of 0.25 μg/ml, an MIC90 of 0.5 μg/ml, and a highest MIC value of 1 μg/ml (Table 3). MBL-producing isolates were also very susceptible to aztreonam-avibactam (MIC50 of 0.12 μg/ml and MIC90 of 0.5 μg/ml for ex-U.S. isolates), and the highest aztreonam-avibactam MIC value among ex-U.S. OXA-48-like-producing isolates was only 0.5 μg/ml (Table 3). In summary, all CRE isolates, including all carbapenemase-producing Enterobacteriaceae strains (U.S. and ex-U.S. strains), were inhibited at aztreonam-avibactam MICs of ≤4 μg/ml.
TABLE 3
TABLE 3 Antimicrobial activity of aztreonam-avibactam tested against carbapenem-resistant Enterobacteriaceae isolates stratified by carbapenemase type
Organism and groupaNo. of isolates (cumulative %)MIC50 (μg/ml)MIC90 (μg/ml)
MIC of ≤0.03 μg/mlMIC of 0.06 μg/mlMIC of 0.12 μg/mlMIC of 0.25 μg/mlMIC of 0.5 μg/mlMIC of 1 μg/mlMIC of 2 μg/mlMIC of 4 μg/ml
United States          
    All CRE isolates (n = 120)23 (19.2)11 (28.3)35 (57.5)28 (80.8)14 (92.5)6 (97.5)1 (98.3)2 (100.0)0.120.5
    KPC producers (n = 102)20 (19.6)10 (29.4)32 (60.8)25 (85.3)11 (96.1)4 (100.0)  0.250.5
    SME-4 producers (n = 2)  1 (50.0)1 (100.0)    0.12 
    MBL producers (n = 2)1 (50.0)0 (50.0)0 (50.0)0 (50.0)0 (50.0)1 (100.0)  ≤0.03 
    Carbapenemase-negative isolates (n = 14)2 (14.3)1 (21.4)2 (35.7)2 (50.0)3 (71.7)1 (78.6)1 (85.7)2 (100.0)0.254
Worldwide (ex-U.S. isolates)          
    All isolates (n = 116)9 (7.8)9 (15.5)38 (48.3)49 (90.5)8 (97.4)0 (97.4)2 (99.1)1 (100.0)0.250.25
    OXA-48-like producers (excluding MBL producers) (n = 57)b2 (3.5)2 (7.0)17 (36.8)32 (93.0)4 (100.0)   0.250.25
    MBL producers (n = 59)c7 (11.9)7 (23.7)21 (59.3)17 (88.1)4 (94.9)0 (94.9)2 (98.3)1 (100.0)0.120.5
a
CRE, carbapenem-resistant Enterobacteriaceae; MBL, metallo-β-lactamase.
b
Includes 55 OXA-48-producing strains, 1 OXA-244-producing strain, and 1-OXA-370-producing strain.
c
Includes 36 NDM-1-producing strains, 7 NDM-7-producing strains, 7 VIM-1-producing strains, 3 NDM-1- plus OXA-232-producing strains, 2 NDM-5- plus OXA-232-producing strains, 2 IMP-4-producing strains, 1 NDM-1- plus OXA-48-producing strain, and 1 NDM-6-producing strain.
Whole-genome sequencing (WGS) results for the isolate with the aztreonam-avibactam MIC of 8 μg/ml showed three serine β-lactamase genes (blaCMY-42, blaOXA-1/30, and blaTEM-1). WGS results also showed a 4-amino-acid insertion in penicillin-binding protein 3 (PBP3) (Y334_R335insRIKY) (14). Additionally, this isolate displayed reduced expression of OmpF and alterations in OmpC, whereas expression of the AcrAB-TolC multidrug efflux pump was similar to baseline levels.
For many years, treatments for CRE infections relied on various combination regimens, with sparse clinical data to support their use (1). In terms of in vitro activity, colistin, tigecycline, fosfomycin, and some aminoglycosides are among the few agents that may remain active against these organisms; however, these compounds have important spectrum deficiencies and/or toxicity issues that prevent their use for empirical treatment of life-threatening infections.
The results of this investigation, coupled with results from previous studies on the in vitro activity of aztreonam-avibactam against carbapenemase-producing strains (1517), indicate that this combination provides universal coverage against β-lactamase-producing Enterobacteriaceae. Only 1 (0.01%) of 10,451 isolates showed an elevated aztreonam-avibactam MIC value, i.e., an E. coli isolate with an aztreonam-avibactam MIC of 8 μg/ml that displayed three serine-β-lactamase genes (blaCMY-42, blaOXA-1/30, and blaTEM-1), membrane porin alterations, and a 4-amino-acid insertion in PBP3 (Y334_R335insRIKY).
NDM-producing E. coli isolates with decreased susceptibility to aztreonam-avibactam were characterized by Alm et al. (14), and their results indicated that decreased susceptibility was not due to aztreonam hydrolysis by NDM-1 or the serine-β-lactamases found in the isolates. Rather, it was caused by a 4-amino-acid insertion in PBP3. This PBP3 alteration appears to affect the accessibility of the transpeptidase binding site to multiple β-lactam compounds, and it is not related to the presence of blaNDM-like or other serine-β-lactamase genes (14). Furthermore, aztreonam-avibactam has demonstrated activity against a large collection of porin-deficient serine-β-lactamase-producing strains from France (18).
Currently available therapeutic options to treat infections caused by antimicrobial-resistant Gram-negative organisms are very limited, due, in part, to the emergence and dissemination of CRE. Results on the in vitro activity of aztreonam combined with avibactam presented here and currently available clinical data for aztreonam used alone (7, 8) and for avibactam used in combination with ceftazidime (35) indicate that aztreonam-avibactam may represent a valuable option for treating infections caused by CRE, MDR Enterobacteriaceae, and XDR Enterobacteriaceae, including MBL-producing strains.

ACKNOWLEDGMENTS

This study was supported by Allergan. Allergan was involved in the design and decision to present these results, and JMI Laboratories received fees for services in relation to preparing the manuscript. Allergan had no involvement in the collection, analysis, and interpretation of the data.
In 2016, JMI Laboratories contracted to perform services for Achaogen, Actelion, Allecra Therapeutics, Allergan, AmpliPhi Biosciences, API, Astellas Pharma, AstraZeneca, Basilea Pharmaceutica, Bayer AG, BD, Biomodels, Cardeas Pharma Corp., CEM-102 Pharma, Cempra, Cidara Therapeutics, Inc., CorMedix, CSA Biotech, Cutanea Life Sciences, Inc., Debiopharm Group, Dipexium Pharmaceuticals, Inc., Entasis Therapeutics, Inc., Fortress Biotech, Fox Chase Chemical Diversity Center, Inc., Geom Therapeutics, Inc., GSK, Laboratory Specialists, Inc., Medpace, Melinta Therapeutics, Inc., Merck & Co., Inc., Micromyx, MicuRx Pharmaceuticals, Inc., Motif Bio, N8 Medical, Inc., Nabriva Therapeutics, Inc., Nexcida Therapeutics, Inc., Novartis, Paratek Pharmaceuticals, Inc., Pfizer, Polyphor, Rempex, Scynexis, Shionogi, Spero Therapeutics, Symbal Therapeutics, Synlogic, TenNor Therapeutics, TGV Therapeutics, The Medicines Company, Theravance Biopharma, ThermoFisher Scientific, VenatoRx Pharmaceuticals, Inc., Wockhardt, and Zavante Therapeutics, Inc. There are no speakers' bureaus or stock options to declare.

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Information & Contributors

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Published In

cover image Antimicrobial Agents and Chemotherapy
Antimicrobial Agents and Chemotherapy
Volume 62Number 1January 2018
eLocator: 10.1128/aac.01856-17

History

Received: 5 September 2017
Returned for modification: 4 October 2017
Accepted: 19 October 2017
Published online: 21 December 2017

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Keywords

  1. carbapenem-resistant Enterobacteriaceae
  2. CRE
  3. KPC
  4. metallo-β-lactamase
  5. NDM-1
  6. OXA-48

Contributors

Authors

Helio S. Sader
JMI Laboratories, North Liberty, Iowa, USA
Rodrigo E. Mendes
JMI Laboratories, North Liberty, Iowa, USA
Michael A. Pfaller
JMI Laboratories, North Liberty, Iowa, USA
University of Iowa, Iowa City, Iowa, USA
Dee Shortridge
JMI Laboratories, North Liberty, Iowa, USA
Robert K. Flamm
JMI Laboratories, North Liberty, Iowa, USA
Mariana Castanheira
JMI Laboratories, North Liberty, Iowa, USA

Notes

Address correspondence to Helio S. Sader, [email protected].

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