TABLE 3

Ceftazidime-avibactam MICs among KPC-Kp, stratified by mutations in ompK35 and ompK36 outer membrane porin genes and KPC typea

Organism/group (n)No. (%) of isolates with ceftazidime-avibactam MICsb (μg/ml) of:MIC50 (μg/ml)MIC90 (μg/ml)
0.250.5124c8d
All KPC-Kp (n = 92)4 (4)2 (2)27 (29)38 (41)20 (22)1 (1)24
Mutations in ompK35 and ompK36
    Wild type (n = 15)4 (27)2 (13)7 (47)2 (13)0012
    ompK35 mutation only (n = 46)e0018 (39)20 (43)7 (15)1 (2)24
    ompK35 and ompK36 mutations (n = 31)e002 (6)16 (52)13 (42)024
KPC-2 (n = 44)f1 (2)2 (5)21 (48)19 (43)1 (2)012
    Wild type (n = 9)1 (11)2 (22)5 (56)1 (11)0011
    ompK35 mutation only (n = 25)0014 (56)10 (40)1 (4)012
    ompK35 and ompK36 mutations (n = 10)002 (20)8 (80)0022
KPC-3 (n = 48)f3 (6)06 (13)19 (40)19 (40)1 (2)24
    Wild type (n = 6)3 (50)02 (33)1 (33)000.52
    ompK35 mutation only (n = 21)004 (19)10 (48)6 (29)1 (5)24
    ompK35 and ompK36 mutations (n = 21)0008 (38)13 (62)044
  • a KPC-Kp, Klebsiella pneumoniae carbapenemase-producing Klebsiella pneumoniae.

  • b A fixed concentration of 4 μg/ml of avibactam was used to determine ceftazidime-avibactam MICs.

  • c The Clinical and Laboratory Standards Institute susceptible breakpoint for ceftazidime and Enterobacteriaceae is 4 μg/ml.

  • d The U.S. FDA susceptible breakpoint for ceftazidime-avibactam and Enterobacteriaceae is 8/4 μg/ml.

  • e Ceftazidime-avibactam MICs for KPC-Kp with ompK35 and ompK36 mutations were greater than those for KPC-Kp with ompK35 mutations only (P < 0.001). MICs for KPC-Kp with OmpK35 mutations only were greater than those for KPC-Kp with wild-type genes (P < 0.001).

  • f Ceftazidime-avibactam MICs for KPC-3-Kp were greater than those for KPC-2-Kp (P < 0.001).