Effect of In Vitro Testing Parameters on Ceftazidime-Avibactam Minimum Inhibitory Concentrations
Table 3
Meropenem MICs with variable testing parameters.
Organism
Isolate #
Genotype
Meropenem 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
0.016
0.016
0.125
0.125
0.06
0.03
0.03
0.03
0.016
0.03
0.03
E. coli
CML2255
CTX-M-15, TEM-1, OXA-1
≤0.06
≤0.06
0.25
0.125
≤0.06
≤0.06
≤0.06
≤0.06
≤0.06
≤0.06
≤0.06
E. coli
CML1468
KPC
4
1
>8
1
4
4
4
8
2
4
4
K. pneumoniae
ATCC 700603
SHV-18
0.03
0.016
0.06
0.06
0.03
0.06
0.25
0.03
0.016
0.016
0.03
K. pneumoniae
CML138
CTX-M-15
≤0.06
≤0.06
2
0.125
0.125
≤0.06
≤0.06
≤0.06
≤0.06
≤0.06
≤0.06
K. pneumoniae
CML128
KPC-2, SHV-27, TEM-1
>64
32
>64
64
>64
>64
64
>64
32
64
64
K. pneumoniae
CML148
ΔKPC-2, SHV-27, TEM-1
0.25
0.25
4
0.25
0.25
0.5
0.25
0.25
0.125
0.25
0.125
K. pneumoniae
CML2280
CTX-M-15, TEM-1, OXA-1
0.06
0.03
0.5
0.125
0.06
0.06
0.06
0.06
0.06
0.125
0.06
K. oxytoca
CML2251
TEM-129
≤0.06
≤0.06
4
0.125
≤0.06
≤0.06
2
≤0.06
0.25
0.5
≤0.06
P. aeruginosa
ATCC 27853
WT
0.5
0.5
0.5
0.5
0.25
0.5
0.5
0.5
0.5
0.25
0.25
P. aeruginosa
CML1039
AmpC
64
32
64
8
32
64
32
32
32
32
32
P. aeruginosa
CML1040
AmpC, TEM-24
4
4
8
4
4
8
4
4
4
8
8
P. aeruginosa
CML1047
AmpC
16
16
16
4
4
32
16
16
8
16
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.