Time kill-assays of antibiotic combinations for multidrug resistant clinical isolates of OXA-48 carbapenemase producing Klebsiella pneumoniae

Abstract

ABSTRACTTreatment of infections caused by OXA-48 carbapenemase producing multidrug-resistant isolates often necessitates combination therapy. In vitro effect of different antibiotic combinations against multidrugresistant (MDR) Klebsiella pneumoniae isolates were evaluated in this study.Meropenem-tobramycin (MERþTOB), meropenem-ciprofloxacin (MERþCIP), colistin-meropenem( COLþMER), colistin-ciprofloxacin (COLþCIP) and colistin-tobramycin (COLþTOB) combinations were tested by time kill-assays. Each antibiotic alone and in combination at their Cmax values were tested against 4 clinical K. pneumoniae isolates at 1, 2, 4, 6, 8, 12 and 24 h. Effect of colistin and its associations were also assessed at 30 min. Bactericidal activity was defined as ≥3log10 CFU mL1 decrease compared with initial inoculum. Synergy was defined as ≥2log10CFU mL1 decrease by the combination compared with the most active single agent. Presence of blaOXA-48, blaNDM, blaVIM, blaIMP, blaKPC and blaCTX-M-1 genes was screened by PCR using specific primers. The blaOXA-48 gene was identified together with blaCTXM-1 group gene in all isolates. COLþMER demonstrated to be synergistic and bactericidal. MERþTOB showed synergistic and bactericidal effect on two strains although, regrowth was seen on other two strains at 24 h. MERþCIP exhibited indifferent effect on the strains.Combination therapy could be a potential alternative to treat MDR K.pneumoniae infections. This combination might prevent resistance development and secondary effects of colistin monotherapy. MERþTOB and MERþCIP might have an isolate-dependent effect, that may not always result in synergism.