Menthol Inhibits Candida albicans Growth by Affecting the Membrane Integrity Followed by Apoptosis
Table 2
Inhibition of planktonic growth (A) of Candida albicans isolates and strains (n = 16), biofilm progression (development and maturation) of C. albicans (ATCC 10231) (B) by menthol alone and in combination with FLC (C).
Assay
Planktonic growth
Number of isolates
A. Broth micro dilution assay
MIC of menthol (mM)
Susceptible (N = 8)
S-DD (N = 2)
Resistant (N = 6)
1.79
3
—
2
3.58
5
2
4
B. Biofilm assay
Biofilm formation (%)
Menthol (mM)
0
3.58
7.16
14.32
28.65
57.3
Developing biofilm
100 ± 0
21 ± 9.24
14 ± 0.97
13 ± 0.65
12 ± 1.14
12 ± 0.32
Mature biofilm
100 ± 0
45 ± 11
30 ± 5.17
25 ± 2.08
25 ± 3.78
25 ± 7.02
C. Synergistic assay
C1. Planktonic growth (MIC)
Combinations
MIC FLZ (mg/L)
Menthol (mM)
FICs FLZ
Menthol
FICI
Interaction
FLZ alone
128
0.0
1.0
0.0
1.0
NI
Menthol + FLZ
8.0
0.44
0.062
0.12
0.182
S
Menthol alone
0.0
3.58
0.0
1.0
1.0
NI
C2. Developing biofilm (MIC90)
FLZ alone
≥256
0.0
1.0
0.0
1.0
NI
Menthol + FLZ
8.0
1.79
0.031
0.062
0.093
S
Menthol alone
0.0
28.65
0.0
1.0
1.0
NI
C3. Matured biofilm (MIC70)
Menthol + FLZ
8.0
1.79
0.031
0.031
0.093
S
Menthol alone
0.0
28.65
0.0
1.0
1.0
NI
MIC of menthol is fungicidal; thus, MIC and minimum fungicidal concentration (MFC) is same. S-DD: susceptible dose-dependent to fluconazole (According to CLSI M27 A3). Stage of development: Developing biofilm = 24 h. Mature biofilm = 48 h. FIC = fractional inhibitory concentrations. FICI = ∑FICs. FLZ = fluconazole. (FICI value ≤ 0.5 = Synergy. FICI ≥0.5- ≤4.0 = No interaction and FICI ≥4 = antagonistic [22].
