Effect of In Vitro Testing Parameters on Ceftazidime-Avibactam Minimum Inhibitory Concentrations
Table 2
Piperacillin-tazobactam MICs with variable testing parameters.
Organism
Isolate #
Genotype
Piperacillin-tazobactam 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
2
2
4
8
4
2
2
2
2
2
4
E. coli
CML2255
CTX-M-15, TEM-1, OXA-1
32
16
512
64
128
16
16
64
32
32
64
E. coli
CML1468
KPC
>512
512
>512
256
>512
512
512
>512
>512
>512
>512
K. pneumoniae
ATCC 700603
SHV-18
16
8
16
64
64
8
16
16
16
16
8
K. pneumoniae
CML138
CTX-M-15
>512
>512
>512
>512
>512
16
>512
>512
>512
>512
>512
K. pneumoniae
CML128
KPC-2, SHV-27, TEM-1
>512
>512
>512
>512
>512
>512
>512
>512
>512
>512
>512
K. pneumoniae
CML148
ΔKPC-2, SHV-27, TEM-1
256
64
>512
256
256
16
64
256
128
128
256
K. pneumoniae
CML2280
CTX-M-15, TEM-1, OXA-1
>512
256
>512
>512
>512
32
>512
>512
>512
>512
>512
K. oxytoca
CML2251
TEM-129
>512
>512
>512
512
>512
256
>512
>512
>512
>512
>512
P. aeruginosa
ATCC 27853
WT
4
4
8
8
4
4
2
2
2
4
4
P. aeruginosa
CML1039
AmpC
512
512
>512
128
512
>512
512
512
512
512
512
P. aeruginosa
CML1040
AmpC, TEM-24
64
64
256
256
256
32
64
64
64
128
256
P. aeruginosa
CML1047
AmpC
>512
512
>512
128
512
>512
512
512
>512
>512
256
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.
