Antibacterial Activities and Synergistic Interaction of Citrus Essential Oils and Limonene with Gentamicin against Clinically Isolated Methicillin-Resistant Staphylococcus aureus

Abstract

Citrus reticulata Blanco and Citrus aurantifolia are the edible plants which contain several biological properties including antibacterial activity. The aims of the present study were to determine the chemical compositions and evaluate antibacterial activities of citrus essential oils extracted from the fruit peels of C. reticulata (CREO) and C. aurantifolia (CAEO), alone and in combination with gentamicin, against a panel of clinically isolated methicillin-resistant S. aureus (MRSA) (n = 40) and methicillin-susceptible S. aureus (MSSA) (n = 45). Gas chromatography-mass spectrometry analysis revealed that 12 and 25 compounds were identified in CREO and CAEO with the most predominant compound of limonene (62.9–72.5%). The antibacterial activities were determined by agar disk diffusion and resazurin-based microdilution methods. The results found that almost all MRSA isolates were resistant to ciprofloxacin, erythromycin, and clindamycin, and some isolates were resistant to gentamicin. CREO and CAEO exhibited inhibitory effects toward clinical isolates (MIC: 1.0–32.0 and 8.0–32.0 mg/mL, respectively), with a similar trend to limonene (MIC: 1.0–32.0 mg/mL). However, the higher antibacterial effects were found in CREO and limonene when compared to CAEO (p < 0.01). In combination effect, the results showed the synergistic interaction of gentamicin with CREO and limonene on the MRSA and MSSA isolates (FIC indexes: 0.012–0.258 and 0.012–0.375), but that interaction of gentamicin with CAEO was observed only on MRSA (FIC index: 0.012–0.016). These findings demonstrated the potential of these citrus essential oils as natural antibacterial agents that may contribute to reduce the emerging of antimicrobial-resistant bacteria.

Antibacterial efficacy of Citrus hystrix (makrut lime) essential oil against clinical multidrug-resistant methicillin-resistant and methicillin-susceptible Staphylococcus aureus isolates

“…The monoterpenes can be found in various citrus plants and contain anti-staphylococcal properties ( Badawy et al, 2019 ). In addition, d-limonene has been reported to have antibacterial activity against MRSA ( Sreepian et al, 2022 ). However, the antibacterial activity of CHEO might result from the interaction between its various components which produces a synergistic effect ( Bassolé and Juliani, 2012 , Cox et al, 2000 ).…”

“…The checkerboard titration assay was performed to evaluate the synergistic interaction between CHEO and gentamicin against the clinical isolates of S. aureus . The method is based on the resazurin-based microdilution method with a final volume of 100 µL ( Sreepian et al, 2022 ). Briefly, 25 µL of various concentrations of CHEO (0.3–32.0 mg/mL) were prepared by serial 2-fold dilution in 96-well microplate.…”

Potent Anti-Cutibacterium acnes Activity of the Essential Oils Derived from Allium sativum, Gerdenia jasminoides, and Hedychium coronarium Cultivated in Thailand

“…A MBC of the extract that indicated no bacterial growth in agar plates was observed (Singh et al 2011). The MIC indices were calculated using MBC/ MBC values to indicate the mode of action, including bactericidal (MIC index < 4) and bacteriostatic (MIC index ≥ 4) (Sreepian et al 2022).…”

Synergistic and Antibiofilm Effects of the Essential Oil from Croton conduplicatus (Euphorbiaceae) against Methicillin-Resistant Staphylococcus aureus

“…Several studies evidence the inhibition of MSSA and MRSA strains by EOs and the synergistic relationship between EOs and antibacterials, highlighting their efficiency [ 3 , 10 , 11 ].…”