Effect of In Vitro Testing Parameters on Ceftazidime-Avibactam Minimum Inhibitory Concentrations
Table 1
Ceftazidime-avibactam MICs with variable testing parameters.
Organism
Isolate #
Genotype
Ceftazidime-avibactam MIC (µg/mL)
Standard
5 × 104 CFU/mL
5 × 106 CFU/mL
pH 5
pH 6
pH 8
CAMHB + 2.5% LHB
HTM
Trace calcium
50 mg/L calcium
CO2
E. coli
ATCC 25922
WT
0.5
0.25
0.5
2
1
0.25
0.5
0.5
0.25
0.5
0.25
E. coli
CML2255
CTX-M-15, TEM-1, OXA-1
0.125
0.06
0.5
0.5
0.25
0.25
0.125
0.25
0.25
0.25
0.5
E. coli
CML1468
KPC
0.5
0.5
4
2
1
1
1
1
0.5
0.5
0.5
K. pneumoniae
ATCC 700603
SHV-18
1
1
2
4
4
1
1
1
1
1
1
K. pneumoniae
CML138
CTX-M-15
1
1
1
1
2
0.5
1
1
1
1
1
K. pneumoniae
CML128
KPC-2, SHV-27, TEM-1
1
1
2
4
4
1
0.5
4
1
1
2
K. pneumoniae
CML148
ΔKPC-2, SHV-27, TEM-1
0.25
0.25
0.5
4
1
0.5
0.125
0.25
0.25
0.25
0.25
K. pneumoniae
CML2280
CTX-M-15, TEM-1, OXA-1
4
2
4
2
4
2
2
2
4
2
2
K. oxytoca
CML2251
TEM-129
1
1
1
1
2
1
1
1
1
1
2
P. aeruginosa
ATCC 27853
WT
2
2
4
2
2
2
2
2
2
2
2
P. aeruginosa
CML1039
AmpC
8
4
16
2
8
4
8
8
8
4
16
P. aeruginosa
CML1040
AmpC, TEM-24
2
2
4
4
4
2
2
2
2
4
4
P. aeruginosa
CML1047
AmpC
8
4
>16
2
8
8
8
4
4
8
8
MICs obtained under standard CLSI conditions are indicated by the “standard” column header. Parameters that were varied include inoculum density (5 × 104 CFU/mL and 5 × 106 CFU/mL), pH of medium (pH 5, 6, and 8), medium supplements (2.5% laked horse blood (LHB) and HTM), cation content (trace amounts of calcium and 50 mg/L calcium), and incubation with 5% CO2. Bolded values indicate a change in MIC of ≥4-fold.
