The in vitro activity of polymyxin B and tigecycline alone and combination with other antibiotics against carbapenem-resistant Enterobacter cloacae complex isolates, including high-risk clones

Yongxin Zhao, Chunjiang Li, Jisheng Zhang, Yanjun Fu, Kewang Hu, Shanshan Su, Yong Wang, Huiling Li, Xiaoli Zhang


Background: The emergence of carbapenem-resistant Enterobacteriaceae (CRE) has become a significant problem for global public health. Currently, treatments program is minimal. This study aimed to evaluate the molecular mechanisms of carbapenem-resistant Enterobacter cloacae complex isolates (CREC) infections.
Methods: Resistance genes were detected using PCR with specific primers. Multilocus sequence typing (MLST) was also performed. Furthermore, we evaluated the effects of polymyxin B (PMB) and tigecycline (TGC) antibiotics (Abs) alone and in combination with meropenem (MEM), amikacin (AMK), and levofloxacin (LEV) against CREC isolates. The results were then compared with in vitro synergy testing results obtained from time-kill assays (TKAs), and the microdilution checkerboard method.
Results: The synergistic efficiency of PMB + TGC was also evaluated. Abs use clinically achievable concentrations to determine the antibacterial effects of the Ab. Similar sequence type (ST) classifications had a comparably resistant phenotype; PMB-based combination therapy is better than TGC-based combination therapy.
Conclusions: we found that the combination of PMB + AMK is promising for the treatment of AMK- sensitive CREC. The high-risk ST93 carrying the blaKPC-2 gene should be monitored.