Evaluating the effects of Carbapenem-β-Lactamase Inhibitor Combinations in treating Carbapenem-Resistant Gram-Negative Bacterial Infections

Abstract

Background: Gram-negative bacteria are common human pathogens that may cause various complicated infections and can become resistant to carbapenems. This form of resistance is clinically relevant as carbapenems are the last line of safe antimicrobials to be used before resorting to toxic drugs such as colistin. Carbapenem-hydrolyzing enzymes are the β-lactamases responsible for carbapenem resistance. Class A β-lactamases include KPC, Class B β-lactamases include NDM, and Class D β-lactamases include OXA-type carbapenemases. When treating carbapenem-resistant infections, antimicrobial combination therapy has been the solution to avoid using colistin extensively, but its benefit over monotherapy remains controversial. The use of β-lactam-β-lactamase inhibitor (BL-BLI) combinations is an alternative approach to treat carbapenem-resistant infections. In this study, we assessed the effect of three carbapenemase inhibitors: calcium-EDTA (Ca-EDTA), avibactam, and relebactam, were combined with each of imipenem, meropenem, and ertapenem against several bacterial isolates that harbor carbapenem-resistance genes. Methods: Six Acinetobacter baumannii isolates were screened for blaOXA-23-like, blaOXA-24-40, blaOXA-51-like, blaOXA-58, and blaOXA-143-like genes, and eight Enterobacteriaceae isolates were screened for blaOXA-48, blaNDM-1, and blaKPC-2 via PCR amplification. Minimal inhibitory concentrations of carbapenems with corresponding β-lactamase inhibitors for each isolate were determined using broth antimicrobial microdilution testing. Efficacy of the most suitable in vitro treatment regimen of an isolate that harbors blaOXA-48 was tested on 30 BALB-c mice by infecting them with the isolate and treating them appropriately, then monitoring their survival for seven days. Reverse transcription real-time PCR analysis was performed to assess the molecular response of the isolate that harbors blaOXA-48 to the selected treatment regimen under both in vitro and in vivo conditions. Resu