In vitro Synergistic Activity of Antimicrobial Combinations Against blaKPC and blaNDM-Producing Enterobacterales With blaIMP or mcr Genes

Abstract

Carbapenemase-producing Enterobacterales have become a severe public health concern because of their rapidly transmissible resistance elements and limited treatment options. The most effective antimicrobial combinations against carbapenemaseproducing Enterobacterales are currently unclear. Here, we aimed to assess the therapeutic effects of seven antimicrobial combinations (colistin-meropenem, colistin-tigecycline, colistin-rifampicin, colistin-erythromycin, meropenem-tigecycline, meropenem-rifampicin, and meropenem-tigecycline-colistin) against twenty-four carbapenem-producing Enterobacterales (producing bla KPC , bla NDM , coexisting bla NDM and bla IMP , and coexisting mcr-1/8/9 and bla NDM genes) and one carbapenemsusceptible Enterobacterales using the checkerboard assay, time-kill curves, and scanning electron microscopy. None of the combinations were antagonistic. The combination of colistin-rifampicin showed the highest synergistic effect of 76% (19/25), followed by colistin-erythromycin at 60% (15/25), meropenem-rifampicin at 24% (6/25), colistin-meropenem at 20% (5/25), colistin-tigecycline at 20% (5/25), and meropenem-tigecycline at 4% (1/25). The triple antimicrobial combinations of meropenem-tigecycline-colistin had a synergistic effect of 100%. Most double antimicrobial combinations were ineffective on isolates with coexisting bla NDM and bla IMP genes. Meropenem with tigecycline showed no synergistic effect on isolates that produced different carbapenemase genes and were highly resistant to meropenem (92% meropenem MIC ≥ 16 mg/mL). Colistin-tigecycline showed no synergistic effect on Escherichia coli producing bla NDM−1 and Serratia marcescens. Time-kill curves showed that antimicrobial combinations achieved an eradication effect (≥ 3 log 10 decreases in colony counts) within 24 h without regrowth, based on 1 × MIC of each drug. The synergistic mechanism of colistin-rifampicin may involve the colistin-mediated disruption of bacterial membranes, leading to severe alterations in their permeability, then causes more rifampicin to enter the cell and induces cell death. In conclusion, the antimicrobial combinations evaluated in this study may facilitate the successful treatment of patients infected with carbapenemase-producing pathogens.

In vitro Investigation of Antibiotic Combinations against Multi- and Extensively Drug-Resistant Klebsiella pneumoniae

“…In cases with MDR and XDR infections treatment with combinations of two or more antibiotics is often selected [13] due to potential benefits in lowering the sub-MICs and achieving a synergistic effect [35].…”

“…Although the in vitro activity of most combinations may be scored as synergistic, their in vivo effectiveness remains uncertain due to the complexity of the infections such as infection site, pharmacokinetic, and pharmacodynamics characteristics of the drugs [13]. The results from genome sequences and epidemiological data of more than 1700 K. pneumoniae samples isolated from patients in 244 hospitals in 32 countries during the European Survey of Carbapenemase-Producing Enterobacteriaceae demonstrate that carbapenemase acquisition is the main cause of CR and 477 of 682 (69.9%) carbapenemase-positive isolates are concentrated in four clonal lineages (11,15, 101, 258/512) and their derivates [36], [37].…”

“…Understanding the mechanisms of action of antimicrobial agents and resistance mechanisms is crucial for the development of novel antibiotics in the future. Unfortunately, the availability of novel antimicrobials is limited due to the lengthy process of drug discovery and certification [13]. Ultimately, the increase of AMR has led to the urge in discovering alternative therapeutic plans.…”

Losing the Battle but Winning the War: Can Defeated Antibacterials Form Alliances to Combat Drug-Resistant Pathogens?

“…Unlike the potential shown with the carbapenem and polymyxin combinations, carbapenem and tigecycline combination studies have yielded fewer promising results against KPCKP. Numerous in vitro studies failed to observe synergistic killing against KPCKP when a carbapenem was paired with tigecycline [41,48,49], whereas other investigations reported that the use of a carbapenem antagonized the killing of tigecycline [50]. Michail et al tested tigecycline drug combinations in vivo using a murine thigh infection model and concluded that the addition of meropenem antagonized the activity of tigecycline against three of the eight KPCKP strains that were investigated, whereas the addition of rifampin or gentamicin increased the killing of KPCKP by tigecycline [41].…”

“…In addition to dual combinations that are composed of a carbapenem and another agent, several triple combinations that utilize two antibacterials and a carbapenem have been evaluated against KPCKP. Triple combinations of a carbapenem, a polymyxin, and either tigecycline or an aminoglycoside were capable of killing more KPCKP than double combinations in multiple in vitro studies [32,33,49]. Dynamic in vitro models have also suggested that synergy against KPCKP may be achieved with the triple combination of a carbapenem, a polymyxin, and rifampin [39,40].…”