Assessment of combination therapy in BALB-c mice infected by multidrug resistant enterobacteriaceae -

Abstract

Background: Due to the increase in resistance to third generation cephalosporins in extended spectrum β-lactamases (ESBLs) producing Enterobacteriaceae, carbapenems are administered as an alternative treatment for infections caused by Enterobacteriaceae. However, the extensive use of carbapenems led to the emergence of carbapenem resistance among these organisms. Subsequently, treatment options for patients with infections caused by carbapenem resistant Enterobacteriaceae are limited to new drug tigecycline, and the older drugs: rifampicin, colistin, or fosfomycin, although these antibacterial agents proved to be notorious. It is currently debatable whether using these antibacterial agents in combination therapy is more advantagous than monotherapy. To that purpose we attempted to assess in vitro and in vivo, the efficacy of combination therapy on ESBL producing and carbapenem resistant Enterobacteriaceae harboring various ESBL and carbapenemase encoding genes.Methods: Four carbapenem resistant isolates were selected from previous studies; two Klebsiella pneumoniae (one isolate harboring the ESBL blaCTX-M-15 gene and one harboring the carbapenemase blaNDM-1gene), one Escherichia coli isolate harboring the carbapenemase blaOXA-48 gene and one Salmonella isolate harboring the carbapenemase blaKPC-2 gene. Antibacterial susceptibility testing was performed by the disc diffusion method. Minimal Inhibitory Concentration (MIC) and Minimal Bactericidal Concentration (MBC) were determined by the broth dilution method. Antibacterial synergism between the combination of different antibacterial agents was assessed by the double disc diffusion method. Carbapenemase production was tested by the Modified and Re-modified Hodge Tests (MHT and RMHT). Assessment of gene transcript levels was determined by RT-qPCR, in response to selected treatment options (combination and monotherapy) carried out in vitro and in vivo. The efficacy of combination therapy was assessed in vivo by monitoring weight and survival rates in female B