In vitro evaluation of various antibiotic combinations for carbapenemase-producing enterobacteriaceae

Introduction and Aim: Carbapenemase-producing Enterobacteriaceae strains cause carbapenem-resistant infections with high mortality, and the number of these reports is increasing with each passing day. The fact that new antibiotic studies do not have the desired efficiency and the development of resistance to the last choice drugs such as carbapenem have restricted the alternatives in treatment. Therefore, the treatment regimens that are not frequently used due to the indication and toxicity concerns have come to the fore. In this study, it was aimed to obtain guiding data for these dilemmas in treatment by investigating the in vitro efficacy of antibiotics and their combinations which may be effective in carbapenemase-producing Enterobacteriaceae strains. Accordingly, the in vitro efficacy of antibiotics, such as aztreonam, avibactam, apramycin, ceftolozane/tazobactam and colistin, and some combinations of them in Carbapenemase-producing Klebsiella pneumoniae strains was investigated. Material and Method: From among the strains isolated from rectal swab screening cultures and various clinical specimens performed in Sakarya University Training and Research Hospital Medical Microbiology Laboratory, 38 K. pneumoniae strains of the Enterobacteriaceae family, which are resistant to carbapenem, found to produce carbapenemase and are resistant to extensive drugs were included in the study. Bacterial identification and antibiotic susceptibility studies were performed by the VITEK 2® (bioMerieux, France) automated system and broth microdilution method. Carbapenemase production was determined phenotypically by the Modified Hodge Test and genotypically by real-time Polymerase Chain Reaction method (Gene Xpert Carba-R kit, Cepheid, USA). The aztreonam+avibactam combination in all strains and the colistin+apramycin combination in colistin resistant 26 strains were studied by the checkerboard method. The efficacy of ceftolozane/tazobactam combination was determined by the gradient strip test (Liofilchem®, Italy). Results: Aztreonam and avibactam had high MIC values in all strains alone, and all strains were found to be resistant to aztreonam. However, it was determined that aztreonam-avibactam combination had synergistic activity in all strains. It was also observed that the combination MIC values of aztreonam were in 94.7% sensitivity threshold range according to the EUCAST threshold value. Only 2 strains were susceptible to ceftolozane-tazobactam combination, 36 strains were found to be resistant. While apramycin was alone effective in 30/38 (79%) of the strains, 8 strains (21%) were found to be resistant. In the synergy study of colistin-resistant 26 strains performed by the checkerboard method, it was determined that the colistin and apramycin combination had a synergistic effect in 4 (15.3%) of the strains, an antagonist effect in 8 (30.7%) of them and an additive effect in 14 (54%) of them. Conclusion: It was observed that aztreonam-avibactam combination had a high in vitro synergistic activity in carbapenemase-producing K. pneumoniae strains, including metallo-beta-lactamase, and was very promising in treatment. The synergistic activity of the colistin/apramycin combination tested in colistin-resistant strains was found to be low. Nevertheless, the fact that apramycin has low MIC values in these strains alone constitutes a potential for clinical studies and treatment. These drugs may be new treatment options in carbapenemase-producing Enterobacteriaceae strains with limited treatment options. Keywords: Carbapenemase-producing Enterobacteriaceae, K. pneumoniae, aztreonam-avibactam, ceftolozane-tazobactam, apramycin, colistin