# D-Limonene: Promising and Sustainable Natural Bioactive Compound
## 3 Antimicrobial Activities of D-Limonene
### Inhibition of MDR Strains by D-Limonene  
Trials have revealed the potential of D-limonene to resist MDR bacterial and fungal contamination and exhibited synergistic effects with antimicrobials. For clinically isolated MDR _Mycobacterium tuberculosis_ strains T1 1558, H1 47, and Beijing 1, D-limonene at concentrations of 128, 128, and 256 \(\upmu\)g/mL, respectively, inhibited their growth; potentiated the inhibitory effects of antimicrobial drugs ethambutol, rifampicin, and isoniazid; and reduced the MICs by two-fold at subinhibitory concentrations and by eight-fold for the non-resistant strains [78]. In another study, D-limonene was found to have a synergistic effect with gentamicin, reducing the MIC values of resistant _S. aureus_ and _E. coli_ from 13.71 \(\upmu\)g/mL and 30 \(\upmu\)g/mL to 4 \(\upmu\)g/mL and 20.1 \(\upmu\)g/mL, respectively [91]; for MDR fungi, such as _Candida tropicalis_, _Candida parapsilosis_, _Candida metapsilosis_, _Candida travesi_, _Candida lusitanie_, D-limonene in the concentration range of 16-64 \(\upmu\)g/mL can inhibit their growth [92]; and D-limonene acts synergistically with fluconazole to resentisize fluconazole-resistant strains of _C. albicans_ and inhibit their growth and biofilm formation [93]. This \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Categories** & **Species** & **Strain** & **CFU/mL** & **MIC** & **MBC/MFC** & **Ref.** \\ \hline \multirow{8}{*}{Bacteria} & _Mycobacterium_ & H37 Ra & - & 64 \(\upmu\)g/mL & - & [77] \\  & _tuberculosis_ & ATCC 25177 & \(1.5\times 10^{8}\) & 32 \(\upmu\)g/mL & - & [78] \\ \cline{2-6}  & _Enterococcus faecalis_ & - & \(1\times 10^{6}\) & 12.5 mg/mL & - & [73] \\ \cline{2-6}  & _Listeria monocytogenes_ & ATCC 35152 & \(1\times 10^{6}\) & 12.5 mg/mL & - & [73] \\ \cline{2-6}  & _FSCC 178006_ & \(10^{6}\)–\(10^{7}\) & 20 \(\upmu\)L/mL & & [79] \\ \cline{2-6}  & _Streptococcus tuberis_ & - & \(1\times 10^{6}\) & 3.3 mg/mL & 210 mg/mL & [80] \\ \cline{2-6}  & _Streptococcus mutans_ & UA 159 & \(1\times 10^{8}\) & 21 mg/mL & - & [81] \\ \cline{2-6}  & _Lactobacillus acidophilus_ & - & \(1\times 10^{6}\) & 40 mg/mL & 80 mg/mL & [71] \\ \cline{2-6}  & _Salmonella_ & - & \(1\times 10^{6}\) & 1.25 mg/mL & 40 mg/mL & [71] \\ \cline{2-6}  & _Salmonella_ & - & \(1\times 10^{8}\) & 7.81 \(\upmu\)g/mL & - & [23] \\ \cline{2-6}  & _Bacillus subtilis_ & ATCC 6633 & \(1\times 10^{8}\) & 1 \(\upmu\)g/mL & - & [72] \\ \cline{2-6}  & _Saccharomyces cerevisiae_ & ATCC 9763 & \(1\times 10^{8}\) & 0.5 \(\upmu\)g/mL & - & [72] \\ \cline{2-6}  & _Fusarium sporrichoides_ & ITEM 692 & - & 10 \(\upmu\)L/mL & - & [82] \\ \cline{2-6}  & _Fusarium langesthiae_ & ITEM 11020 & - & 5 \(\upmu\)L/mL & - & [82] \\ \cline{2-6}  & _Fusarium graminaarum_ & ITEM 6477 & - & 5 \(\upmu\)L/mL & - & [82] \\ \cline{2-6}  & _Candida albicans_ & ATCC 90028 & - & 0.31 mg/mL & 0.62 mg/mL & [83] \\ \cline{2-6}  & _Candida glabrata_ & ATCC 90030 & - & 0.31 mg/mL & 1.25 mg/mL & [83] \\ \cline{2-6}  & _CATC 27853 & - & 0.31 mg/mL & 1.25 mg/mL & [83] \\ \cline{2-6}  & _Candida paralysilosis_ & URM 6404 & - & 256 \(\upmu\)g/mL & - & [85] \\ \cline{2-6}  & _HAM 26_ & - & 512 \(\upmu\)g/mL & - & [85] \\ \cline{2-6}  & _Candida krusei_ & ATCC 6258 & - & 0.07 mg/mL & 0.62 mg/mL & [83] \\ \cline{2-6}  & _Candida tropicalis_ & SH 1 & \(1\times 10^{7}\) & 20 \(\upmu\)L/mL & 40 \(\upmu\)L/mL & [86] \\ \cline{2-6}  & _Bacillus cereus_ & ATCC 33018 & \(1\times 10^{7}\) & 2.5 mg/mL & \textgreater{}40 mg/mL & [87] \\ \cline{2-6}  & _Pluytophthora capsici_ & LT 263 & \(5\times 10^{4}\) & 20 mg/L & - & [88] \\ \cline{2-6}  & _Trichophyton rubrum_ & KCTC 6345 & \(1\times 10^{5}\) & 5 \(\upmu\)L/mL & - & [89] \\ \cline{2-6}  & _Trichophyton rubrum_ & MTCC 296 & - & 2 \(\upmu\)L/mL & 6 \(\upmu\)L/mL & [90] \\ \cline{2-6}  & _Sclerotinia sclerootomy_ & BRM 29673 & - & 200 \(\upmu\)L/mL & - & [45] \\ \hline \hline \end{tabular}
\end{table}