Abstract
BackgroundCarbapenem-resistant Gram-negative bacteria are a major clinical concern as they cause virtually untreatable infections since carbapenems are among the last-resort antimicrobial agents. β-Lactamases implicated in carbapenem resistance include KPC, NDM, and OXA-type carbapenemases. Antimicrobial combination therapy is the current treatment approach against carbapenem resistance in order to limit the excessive use of colistin; however, its advantages over monotherapy remain debatable. An alternative treatment strategy would be the use of carbapenem/β-lactamase inhibitor (βLI) combinations. In this study, we assessed the in vitro and in vivo phenotypic and molecular efficacies of three βLIs when combined with different carbapenems against carbapenem-resistant Gram-negative clinical isolates. The chosen βLIs were (1) Avibactam, against OXA-type carbapenemases, (2) calcium-EDTA, against NDM-1, and (3) Relebactam, against KPC-2.MethodsSix Acinetobacter baumannii clinical isolates were screened for blaOXA-23-like, blaOXA-24/40, blaOXA-51-like, blaOXA-58, and blaOXA-143-like, and eight Enterobacteriaceae clinical isolates were screened for blaOXA-48, blaNDM-1, and blaKPC-2. The minimal inhibitory concentrations of Imipenem (IPM), Ertapenem (ETP), and Meropenem (MEM) with corresponding βLIs for each isolate were determined. The efficacy of the most suitable in vitro treatment option against each of blaOXA-48, blaNDM-1, and blaKPC-2 was assessed via survival studies in a BALB/c murine infection model. Finally, RT-qPCR was performed to assess the molecular response of the genes of resistance to the carbapenem/βLI combinations used under both in vitro and in vivo settings.ResultsCombining MEM, IPM, and ETP with the corresponding βLIs restored the isolates’ susceptibilities to those antimicrobial agents in 66.7%, 57.1%, and 30.8% of the samples, respectively. Survival studies in mice revealed 100% survival rates when MEM was combined with either Avibactam or Relebactam against blaOXA-48 and blaKPC-2, respectively. RT-qPCR demonstrated the consistent overexpression of blaOXA-48 upon treatment, without hindering Avibactam’s activity, while blaNDM-1 and blaKPC-2 experienced variable expression levels upon treatment under in vitro and in vivo settings despite their effective phenotypic results.ConclusionNew carbapenem/βLI combinations may be viable alternatives to antimicrobial combination therapy as they displayed high efficacy in vitro and in vivo. Meropenem/Avibactam and Meropenem/Relebactam should be tested on larger sample sizes with different carbapenemases before progressing further in its preclinical development.
Highlights
Carbapenem resistant Gram-negative bacteria have been gradually increasing in prevalence in recent years
The Department of Pathology and Laboratory Medicine at the American University of Beirut Medical Center (AUBMC), Beirut, Lebanon provided all of the clinical bacterial isolates included in this study with the exception of one Salmonella spp. isolate that was provided by the Centers for Disease Control and Prevention (CDC), Atlanta, GA, United States
Concerning the survival rate of the BALB/c mice upon infection with the tested isolates and treatment with Meropenem monotherapy in comparison to Meropenem/β-lactamase inhibitor (βLI) combinations, the group receiving Meropenem/Avibactam against E. coli IMP 57 experienced a 100% survival rate (p < 0.0001) when compared to their positive control group (16.7% survival) as well as the group receiving Meropenem monotherapy (0% survival) and the group receiving Avibactam alone (0% survival) (Figure 2)
Summary
Carbapenem resistant Gram-negative bacteria have been gradually increasing in prevalence in recent years. KPC and OXA-type carbapenemases are families of Ambler Class A and Class D serine β-lactamases, respectively, that contain a serine moiety in their active sites (Sahuquillo-Arce et al, 2015). NDM is a family of Ambler Class B metallo-β-lactamases that contain a divalent cation in their active site (Sahuquillo-Arce et al, 2015) with NDM-1 being the most prominent member (Nordmann et al, 2011). Β-Lactamases implicated in carbapenem resistance include KPC, NDM, and OXA-type carbapenemases. We assessed the in vitro and in vivo phenotypic and molecular efficacies of three βLIs when combined with different carbapenems against carbapenem-resistant Gram-negative clinical isolates. The chosen βLIs were (1) Avibactam, against OXA-type carbapenemases, (2) calcium-EDTA, against NDM-1, and (3) Relebactam, against KPC-2
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