In Vitro Activity of KBP-7072, a Novel Third-Generation Tetracycline, against 531 Recent Geographically Diverse and Molecularly Characterized Acinetobacter baumannii Species Complex Isolates.

KBP-7072 is a novel third-generation tetracycline (aminomethylcycline) antibacterial that overcomes common efflux and ribosomal protection resistance mechanisms that cause resistance in older-generation tetracyclines. KBP-7072 completed phase 1 clinical development studies for safety, tolerability, and pharmacokinetics (ClinicalTrials.gov identifier NCT02454361) and multiple ascending doses in healthy subjects (ClinicalTrials.gov identifier NCT02654626) in December 2015. Both oral and intravenous formulations of KBP-7072 are being developed. In this study, we evaluated the in vitro activities of KBP-7072 and comparator agents by CLSI document M07 (2018) broth microdilution against 531 recent geographically diverse and/or molecularly characterized Acinetobacter baumannii-A. calcoaceticus species complex (A. baumannii) isolates from the United States, Europe, Asia-Pacific (excluding China), and Latin America. A. baumannii isolates included carbapenem-resistant, colistin-resistant, tetracycline-resistant, and extended-spectrum-ß-lactamase (ESBL)- and metallo-ß-lactamase (MBL)-producing isolates. Overall, KBP-7072 (MIC50/90, 0.25/1 mg/liter) was comparable in activity to colistin (92.8%/92.8% susceptible [S] [CLSI/EUCAST]) against A. baumannii isolates, inhibiting 99.2% of isolates at ≤2 mg/liter and 97.6% of isolates at ≤1 mg/liter. KBP-7072 was equally active against A. baumannii isolates, including carbapenem-resistant, colistin-resistant, and tetracycline-resistant isolates, regardless of geographic location, and maintained activity against ESBL- and MBL-producing isolates. KBP-7072 outperformed comparator agents, including ceftazidime (40.3% S [CLSI]), gentamicin (48.2%/48.2% S [CLSI/EUCAST]), levofloxacin (39.5%/37.9% S [CLSI/EUCAST]), meropenem (42.0%/42.0% S [CLSI/EUCAST]), piperacillin-tazobactam (33.3% S [CLSI]), and all tetracycline-class comparator agents, which include doxycycline (67.3% S [CLSI]), minocycline (73.8% S [CLSI]), tetracycline (37.2% S [CLSI]), and tigecycline (79.5% inhibited by ≤2 mg/liter). The potent in vitro activity of KBP-7072 against recent geographically diverse, molecularly characterized, and drug-resistant A. baumannii isolates supports continued clinical development for the treatment of serious infections, including those caused by A. baumannii.

Evaluation of the Bactericidal Activity of Fosfomycin in Combination with Selected Antimicrobial Comparison Agents Tested against Gram-Negative Bacterial Strains by Using Time-Kill Curves.

The effects of combining fosfomycin with various antimicrobial agents were evaluated in vitro by broth microdilution checkerboard and time-kill kinetic studies. Checkerboard analyses were used to evaluate the following 30 Gram-negative isolates: 5 Pseudomonas aeruginosa, 5 Acinetobacter baumannii-Acinetobacter calcoaceticus species complex, and 20 Enterobacteriaceae isolates. No isolate exhibited antagonism when fosfomycin was tested in combination, and synergy was observed in more than 25% of the drug combinations tested. The most frequent instances of synergy occurred when testing fosfomycin with ß-lactams. Two isolates of Pseudomonas aeruginosa, 2 of Klebsiella pneumoniae, and 1 of the A. baumannii-A. calcoaceticus species complex that exhibited synergy when fosfomycin was tested in combination were subjected to time-kill kinetic analyses for confirmation. Time-kill assays confirmed synergistic activity. These data indicated that combination therapy with fosfomycin may be beneficial.

In vitro activity of a novel aminomethylcycline antibacterial (KBP-7072), a third-generation tetracycline, against clinical isolates with molecularly characterized tetracycline resistance mechanisms.

OBJECTIVES: This study evaluated the in vitro activity of KBP-7072 against 413 contemporary surveillance isolates, including subsets with known tetracycline resistance genes. MATERIALS: In total, 105 Klebsiella pneumoniae (51 tetracycline resistant), 103 Escherichia coli (52 tetracycline resistant), 103 Staphylococcus aureus (51 tetracycline resistant) and 102 Streptococcus pneumoniae (51 tetracycline resistant) isolates were included. These isolates were tested by broth microdilution using fresh media. CLSI/EUCAST breakpoints were applied, except for tigecycline and omadacycline, which used FDA criteria. RESULTS: KBP-7072 (MIC50, 0.06 mg/L), tigecycline (MIC50, 0.12 and 0.25 mg/L) and omadacycline (MIC50, 0.12 and 0.5 mg/L) showed similar MIC50s for tetracycline-susceptible and -resistant S. aureus. Other tetracycline comparators had their MIC50 increased 64- to 256-fold by tet. For S. pneumoniae, KBP-7072 (MIC50/90, ≤0.015/0.03 mg/L) showed the lowest MICs, which remained unchanged for tetracycline-susceptible or -resistant isolates [mostly tet(M)]. Similar MICs were observed for omadacycline (MIC50/90, 0.03-0.06/0.06 mg/L) and tigecycline (MIC50/90, 0.03/0.03 mg/L) in the S. pneumoniae population. Tetracycline-susceptible and -resistant E. coli [94.2% tet(A)/tet(B)], KBP-7072 (MIC90, 0.25 and 1 mg/L, respectively) and tigecycline (MIC90, 0.25 and 0.5 mg/L) showed similar MIC90s. KBP-7072 (MIC50/90, 0.25/0.5 mg/L) and tigecycline (MIC50/90, 0.5/0.5 mg/L) had the lowest MIC for tetracycline-susceptible K. pneumoniae. The MIC for KBP-7072 (MIC50/90, 1/4 mg/L) and tigecycline (MIC50/90, 1/2 mg/L) increased 2- to 8-fold for tetracycline-resistant K. pneumoniae, which mostly produced Tet(A). CONCLUSIONS: KBP-7072 activity was minimally affected by the presence of acquired tetracycline genes.

In vitro activity of KHP-3757 (a novel LpxC inhibitor) and comparator agents against recent and molecularly characterized Pseudomonas aeruginosa isolates from a global surveillance program (2017-2018).

This study evaluated the in vitro activity of KHP-3757 (a novel LpxC inhibitor) and comparator agents against recent, geographically diverse, Pseudomonas aeruginosa isolates from a global surveillance program as well as molecularly characterized extended-spectrum-ß-lactamase-positive, metallo-ß-lactamase-positive, and colistin-resistant strains. KHP-3757 (MIC50/90, 0.25/0.5 mg/L; 97.4% inhibited at ≤0.5 mg/L) demonstrated potent in vitro activity based on MIC90 values against P. aeruginosa isolates including extended-spectrum-ß-lactamase-positive, metallo-ß-lactamase-positive, and colistin-resistant strains outperforming other comparator agents.