Doripenem MICs and ompK36 Porin Genotypes of Sequence Type 258, KPC-Producing Klebsiella pneumoniae May Predict Responses to Carbapenem-Colistin Combination Therapy among Patients with Bacteremia

Treatment failures of a carbapenem-colistin regimen among patients with bacteremia due to sequence type 258 (ST258), KPC-2-producing Klebsiella pneumoniae were significantly more likely if both agents were inactive in vitro, as defined by a colistin MIC of >2 mu g/ml and the presence of either a major ompK36 porin mutation (guanine and alanine insertions at amino acids 134 and 135 [ins aa 134-135 GD], IS5 promoter insertion [P = 0.007]) or a doripenem MIC of >8 mu g/ml (P = 0.01). Major ompK36 mutations among KPC-K. pneumoniae strains are important determinants of carbapenem-colistin responses in vitro and in vivo.