In Vitro Bactericidal Activity of 4- and 5-Chloro-2-hydroxy-N-[1-oxo-1-(phenylamino)alkan-2-yl]benzamides against MRSA
Table 3
Change in viable counts (log10 CFU/mL) of MRSA and S. aureus strains following incubation for 24 h with 5-chloro-2-hydroxy-N-[(2S)-3-methyl-1-oxo-1-{[4-(trifluoromethyl)-phenyl]amino}butan-2-yl]benzamide (1f), N-{(2S)-1-[(4-bromophenyl)amino]-3-methyl-1-oxobutan-2-yl}-4-chloro-2-hydroxybenzamide (1g), and 4-chloro-N-{(2S)-1-[(3,4-dichlorophenyl)amino]-3-methyl-1-oxobutan-2-yl}-2-hydroxybenzamide (1h) (bactericidal effect is expressed in bold).
Strain
MIC/MBC
Conc.
Log10 difference in CFU/mL from inoculum
4 h
6 h
8 h
24 h
Comp. 1f
MRSA 63718
4/4
1× MIC
0.34
0.56
0.66
1.68
2× MIC
−3.08a
−3.33
−3.75
−2.40b
4× MIC
−5.30
−5.30
−5.30
−5.30
MRSA SA 630
2/4
1× MIC
0.65
1.16
1.36
0.65
2× MIC
−0.26
−0.77
−1.40
−2.07
4× MIC
−0.83
−3.26
−2.52
−3.22
MRSA SA 3202
2/8
1× MIC
1.21
1.56
1.75
1.57
2× MIC
0.06
−0.05
−0.65
−1.59
4× MIC
−0.07
−1.05
−2.70
−3.30
S.a.
2/4
1× MIC
0.82
1.00
1.14
1.21
2× MIC
−0.25
−0.74
−1.52
−2.52
4× MIC
−1.17
−2.85
−3.88
−3.65
Comp. 1g
MRSA 63718
8/16
1× MIC
0.43
0.65
0.75
0.95
2× MIC
−2.54
−3.23
−3.15
−0.76
4× MIC
−3.18
−3.58
−3.10
−2.24
MRSA SA 630
4/8
1× MIC
0.98
1.42
1.57
0.55
2× MIC
−0.12
−0.73
−1.50
−0.28
4× MIC
−1.00
−1.54
−2.37
−3.38
MRSA SA 3202
4/8
1× MIC
0.56
1.47
1.70
2.14
2× MIC
−0.03
−0.07
−0.82
−0.69
4× MIC
−0.35
−0.56
−1.49
−4.01
S.a.
4/8
1× MIC
1.02
1.10
1.45
1.57
2× MIC
0.16
0.10
0.80
−0.34
4× MIC
−0.07
−0.11
−1.65
−2.33
Comp. 1h
MRSA 63718
2/4
1× MIC
−0.76
−1.09
−0.71
0.89
2× MIC
−1.77
−2.07
−1.97
0.47
4× MIC
−2.90
−3.54
−3.31
−2.65
MRSA SA 630
1/1
1× MIC
−0.27
−0.10
−0.09
1.42
2× MIC
0.19
−1.19
−1.39
−0.30
4× MIC
−2.72
−3.21
−3.39
−3.18
MRSA SA 3202
1/4
1× MIC
0.27
0.82
0.96
1.12
2× MIC
0.17
−0.27
−0.53
−0.09
4× MIC
−0.35
−1.13
−1.83
−3.02
S.a.
1/2
1× MIC
0.27
0.06
0.00
1.43
2× MIC
0.04
−0.35
−0.94
−1.20
4× MIC
−0.34
−1.29
−2.62
−2.61
CFU: colony-forming units; Conc.: concentration (multiplicity of MIC).
≥3 reduction in CFU implies a bactericidal effect.
<3 reduction in CFU implies a bacteriostatic effect.