TABLE 5.

MICs and cumulative percent inhibited distributions for ceftazidime and ceftazidime-avibactam against multidrug-resistant Klebsiella isolates producing Ambler class A, B, C, or D enzymes^a

^aMDR, multidrug resistance (defined by resistance to three or more drug classes, including classes not included in this analysis); no., number of isolates; Cum%, cumulative percentage inhibited; CAZ, ceftazidime; CAZ-AVI, ceftazidime with 4 μg/ml avibactam. MIC₉₀ values (shaded) are only reported for >10 isolates. The FDA susceptibility breakpoint for ceftazidime-avibactam is MIC ≤8 μg/ml (19).

^b Class A: presence of bla_SHV, bla_TEM, bla_CTX-M, bla_VEB, bla_PER, bla_GES, and/or bla_KPC confirmed by PCR. K. oxytoca isolates are presumed to carry the intrinsic chromosomally encoded bla_OXY common to this species, though this was not confirmed by molecular methods. Class B: presence of bla_VIM, bla_IMP, and/or bla_NDM confirmed by PCR. Class C: presence of bla_ACC, bla_CMY, bla_DHA, bla_FOX, bla_MOX, and/or bla_ACT confirmed by PCR. Class D: presence of bla_OXA-48-like confirmed by PCR. No β-lactamase identified: isolates in which none of the tested β-lactamase genes were detected by PCR. Does not include isolates of K. oxytoca, which are presumed to carry the intrinsic chromosomally encoded bla_OXY.