Doripenem, gentamicin, and colistin, alone and in combinations, against gentamicin-susceptible, KPC-producing Klebsiella pneumoniae strains with various ompK36 genotypes

Abstract

Gentamicin doses of 2 and 10 μg/ml were bactericidal against 64% and 100%, respectively, of gentamicin-susceptible KPC-2-producing Klebsiella pneumoniae strains. Treatment with the combination of doripenem (8 μg/ml) plus colistin (2 μg/ml) was inferior to treatment with gentamicin (2 μg/ml), doripenem-gentamicin, gentamicin-colistin, and doripenem-gentamicin-colistin against strains with glycine and aspartic acid insertions in OpmK36 porin at amino acid (aa) positions 134 and 135 (n = 9). Doripenem-colistin was comparable to other 2- or 3-drug regimens and superior to single drugs against wild-type/minor ompK36 mutants (n = 5). An algorithm incorporating ompK36 genotypes and susceptibility to gentamicin and doripenem may predict antimicrobial activity against KPC-producing K. pneumoniae.

FIG 1

Kill curves of KPC-K. pneumoniae strains by single drugs and combinations. Data represent the median log₁₀ CFU/ml for specific drug regimens over time. There were no differences in growth at 12 and 24 h between strains incubated with DOR and those with no drug control. Note that the kill curves for COL+GENT and DOR+GENT+COL overlap.

FIG 2

Median AUBCs for 2-drug combinations against KPC-K. pneumoniae isolates, stratified by ompK36 genotypes. Shown are time-kill results against ins aa134-135GD mutants (A) and wild-type/minor mutants (B). Data represent the median log₁₀ CFU/ml for specific combinations over time. The black dotted line represents median time-kills by DOR+COL. The solid black line and the thick broken black lines represent median time-kills by DOR+GENT and GENT+COL, respectively. Therefore, the AUBCs highlighted by black-and-white checkers depict the activity of GENT+COL, and AUBCs highlighted by solid gray and gray with black diagonal lines depict the differences observed with DOR+GENT and DOR+COL, respectively.

FIG 3

AUBCs for single drugs and combinations against KPC-K. pneumoniae strains, stratified by ompK36 genotypes. Shown are time-kill results against ins aa134-135GD (A) and wild-type/minor (B) mutants. Data represent median AUBCs with interquartile ranges for specific regimens over time. For ins aa134-135GD mutants, the median AUBCs were higher for DOR+COL than for GENT (P = 0.007), DOR+GENT (P = 0.004), GENT+COL (P = 0.002), and DOR+GENT+COL (P < 0.001). For wild-type/minor mutants, the median AUBCs were not significantly different between DOR+COL, DOR+GENT, GENT+COL, and DOR+GENT+COL.

FIG 4

Proposed algorithm for predicting active antimicrobial regimens against KPC-K. pneumoniae strains. A doripenem MIC of ≤8 μg/ml can be used as a proxy for the presence of wild-type/minor ompK36 mutation, and a doripenem MIC of >8 μg/ml can be used as a proxy for the presence of an ins aa134-135GD mutation. DOR+GENT may offer synergy against some GENT-susceptible wild-type/minor ompK36 mutant strains, but it is not likely to offer synergy over GENT alone against GENT-susceptible ins aa134-135GD mutant strains, since constriction of the porin channel will restrict DOR uptake.