AUTHOR=El Hafi Bassam , Rasheed Sari S. , Abou Fayad Antoine G. , Araj George F. , Matar Ghassan M. 

TITLE=Evaluating the Efficacies of Carbapenem/β-Lactamase Inhibitors Against Carbapenem-Resistant Gram-Negative Bacteria in vitro and in vivo

JOURNAL=Frontiers in Microbiology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2019.00933

DOI=10.3389/fmicb.2019.00933

ISSN=1664-302X

ABSTRACT=<sec><title>Background</title><p>Carbapenem-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 <italic>in vitro</italic> and <italic>in vivo</italic> 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.</p></sec><sec><title>Methods</title><p>Six <italic>Acinetobacter baumannii</italic> clinical isolates were screened for <italic>bla</italic><sub>OXA-23-like</sub>, <italic>bla</italic><sub>OXA-24/40</sub>, <italic>bla</italic><sub>OXA-51-like</sub>, <italic>bla</italic><sub>OXA-58</sub>, and <italic>bla</italic><sub>OXA-143-like</sub>, and eight <italic>Enterobacteriaceae</italic> clinical isolates were screened for <italic>bla</italic><sub>OXA-48</sub>, <italic>bla</italic><sub>NDM-1</sub>, and <italic>bla</italic><sub>KPC-2</sub>. 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 <italic>in vitro</italic> treatment option against each of <italic>bla</italic><sub>OXA-48</sub>, <italic>bla</italic><sub>NDM-1</sub>, and <italic>bla</italic><sub>KPC-2</sub> 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 <italic>in vitro</italic> and <italic>in vivo</italic> settings.</p></sec><sec><title>Results</title><p>Combining 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 <italic>bla</italic><sub>OXA-48</sub> and <italic>bla</italic><sub>KPC-2</sub>, respectively. RT-qPCR demonstrated the consistent overexpression of <italic>bla</italic><sub>OXA-48</sub> upon treatment, without hindering Avibactam’s activity, while <italic>bla</italic><sub>NDM-1</sub> and <italic>bla</italic><sub>KPC-2</sub> experienced variable expression levels upon treatment under <italic>in vitro</italic> and <italic>in vivo</italic> settings despite their effective phenotypic results.</p></sec><sec><title>Conclusion</title><p>New carbapenem/βLI combinations may be viable alternatives to antimicrobial combination therapy as they displayed high efficacy <italic>in vitro</italic> and <italic>in vivo.</italic> Meropenem/Avibactam and Meropenem/Relebactam should be tested on larger sample sizes with different carbapenemases before progressing further in its preclinical development.</p></sec>