Reversal of phenotypic resistance in multi-drug resistant carbapenemase-producing K. pneumoniae clinical isolates due to in vitro synergistic interactions between bacteriophages and antibiotics at clinically achievable concentrations.

Abstract

Background: Therapeutic options for MDR carbapenemase-producing Klebsiella pneumoniae (CRKP) are limited. We therefore assessed the in vitro activity of five antibiotics from different classes in combination with lytic bacteriophages (phages) against MDR CRKP isolates.

Material and methods: A total of 15 non-repetitive, well-characterized MDR CRKP isolates and four phages belonging to the Podoviridae family were used in chequerboard assays with amikacin, meropenem, ciprofloxacin, colistin and ceftazidime/avibactam. The spectrophotometrically determined MIC of drugs and phages alone and in combination were used to calculate the fractional inhibitory concentration index (FICi). The clinical relevance was assessed based on the MIC reductions at clinically achievable concentrations and below the corresponding susceptibility breakpoints. Emergence of resistance was studied in growth curves and time-kill experiments.

Results: Synergy was found for ciprofloxacin in 6/15 (40%) isolates, meropenem in 10/15 (67%), ceftazidime/avibactam in 11/15 (73%), colistin in 8/15 (53%) and amikacin in 9/15 (60%) with all four phages against host bacteria. The synergistic interactions were strong as the FICi were 0.01-0.35 reducing the MICs (>90% growth inhibition) to clinically achievable concentrations for 87%-100% of strains, except ciprofloxacin. Reversal of phenotypic resistance was observed for amikacin, meropenem, colistin and ceftazidime/avibactam in 100%, 53%, 89% and 80% of isolates, respectively. No emergence of resistance was found for isolates with low level resistance to amikacin (MΙC 64 mg/L).

Conclusions: The phage-antibiotic combinations were synergistic against more than half of the isolates for all antibiotics except ciprofloxacin reversing resistance in most strains particularly with amikacin.