Mutations of theompK36Porin Gene and Promoter Impact Responses of Sequence Type 258, KPC-2-Producing Klebsiella pneumoniae Strains to Doripenem and Doripenem-Colistin

Abstract

ABSTRACTDoripenem-colistin exerts synergy against some, but not all,Klebsiella pneumoniaecarbapenemase (KPC)-producingK. pneumoniaestrainsin vitro. We determined if doripenem MICs and/orompK36porin gene mutations impacted the responses of 23 sequence type 258 (ST258), KPC-2-producing strains to the combination of doripenem (8 μg/ml) and colistin (2 μg/ml) during time-kill assays. The median doripenem and colistin MICs were 32 and 4 μg/ml. Doripenem MICs did not correlate with KPC-2 expression levels. Five and 18 strains had wild-type and mutantompK36, respectively. The most common mutations were IS5promoter insertions (n= 7) and insertions encoding glycine and aspartic acid at amino acid (aa) positions 134 and 135 (ins aa134-135 GD;n= 8), which were associated with higher doripenem MICs than other mutations or wild-typeompK36(allPvalues ≤ 0.04). Bactericidal activity (24 h) was achieved by doripenem-colistin against 12%, 43%, and 75% of ins aa134-135 GD, IS5, and wild-type/other mutants, respectively (P= 0.04). Doripenem-colistin was more active in time-kill studies than colistin at 12 and 24 h if the doripenem MIC was ≤8 μg/ml (P= 0.0007 and 0.09, respectively), but not if the MIC was >8 μg/ml (P= 0.10 and 0.16). Likewise, doripenem-colistin was more active at 12 and 24 h against the wild type/other mutants than ins aa134-135 GD or IS5mutants (P= 0.007 and 0.0007). By multivariate analysis, the absence of ins aa134-135 GD or IS5mutations was the only independent predictor of doripenem-colistin responses at 24 h (P= 0.002). In conclusion,ompK36genotypes identified ST258 KPC-K. pneumoniaestrains that were most likely to respond to doripenem-colistin.