School of Therapeutic Sciences (ETDs)

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Browsing School of Therapeutic Sciences (ETDs) by Keyword "Antimicrobial"

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    Essential oil compounds in combination with conventional antibiotics for dermatology
    (University of the Witwatersrand, Johannesburg, 2024) Simbu, Shivar Bram; Van Vuuren, Sandy
    Skin and soft tissue infections represent a heterogeneous array of clinical entities with varying severity, causative pathogens, and rates of progression. The slow development and overuse of antimicrobial agents have perpetuated the spread and severity of antimicrobial resistance. Natural products such as essential oils and their compounds are often investigated for their pharmacological properties, with particular interest in their antimicrobial properties. This study aimed to investigate the effects of combining six essential oil compounds (α-pinene, γ-terpinene, ±linalool, eugenol, carvacrol, and cinnamaldehyde) with eight conventional antimicrobials (amoxicillin, ciprofloxacin, erythromycin, gentamicin, meropenem, tetracycline, miconazole, and nystatin) against six commonly encountered skin pathogens (Staphylococcus aureus ATCC 25923, Staphylococcus epidermidis ATCC 12228, Pseudomonas aeruginosa ATCC 27853, Acinetobacter baumannii ATCC 19606, Cutibacterium acnes ATCC 11827, and Candida albicans ATCC 10231) to elucidate the interactive profiles, toxicity, and anti-inflammatory properties. The antimicrobial analysis involved determining the minimum inhibitory concentrations (MIC) of the conventional antimicrobials and essential oil compounds, singularly and in combination, using the broth microdilution assay. The sum of the fractional inhibitory concentrations (ΣFICs) was calculated to investigate the interactive profile of the combinations. Synergistic interactions were further analysed at varying ratios and depicted on isobolograms. Eight synergistic interactions were identified, with seven against Gram-positive bacteria (ΣFIC 0.07– 0.42) and one against P. aeruginosa (ΣFIC 0.32). In addition, it was demonstrated that when in combination, the selected combinations resulted in reduced toxicity (Brine-shrimp lethality assay). The combination of amoxicillin and eugenol demonstrated the lowest toxicity (LC50 = 1081 μg/mL) and the highest selectivity index (14.41) when in a (70:30) ratio with the antibiotic in the higher ratio. Based on the synergistic results from the antimicrobial analysis, a selection of essential oil compounds with conventional antimicrobials were assessed for cytotoxicity and anti- inflammatory properties. The cytotoxicity properties were determined using the MTT assay on HaCAT keratinocytes. The anti-inflammatory properties were determined using lipopolysaccharide (LPS) activated RAW 264.7 macrophages, and the reduction in nitrate (NO) production was measured. Cinnamaldehyde demonstrated the highest cytotoxicity (IC50 = 28.63 μg/mL, p < 0.05) and the greatest reduction (77.44%) in nitrite production, which was also concentration dependent. The combination of ciprofloxacin and cinnamaldehyde demonstrated the lowest cytotoxicity (88.42% ± 3.72 cell viability; combination index of 0.12) and the highest reduction in nitrite production (77.42%; ΣFa = 0.44). Further investigations on the interactive properties of ibuprofen were undertaken. The antimicrobial, cytotoxicity, and anti-inflammatory properties of ibuprofen were analysed singularly and in combination with all essential oil compounds and conventional antimicrobials against reference and clinical skin pathogens. For the MIC results, four synergistic interactions were identified between ibuprofen and conventional antimicrobials (ΣFIC 0.33 - 0.50). For the cytotoxicity (MTT assay), none of the combinations demonstrated a cytotoxic effect (cell viability of 93.6-100%) and significant reduction on nitric oxide production. Additionally, higher order combinations involving the synergistic combinations were investigated with the inclusion of the essential oil compounds. Three synergistic interactions were identified (One against C. acnes and two against A. baumannii). The triple combinations were slightly cytotoxic (cell viability of 77.59 - 90.44%; combination index of 0.95 -1.10) on the HaCAT cell line and did not reduce nitric oxide production. Based on the overall results from this study, combinations of essential oil compounds and some conventional antimicrobials demonstrate promising therapeutic approaches to attenuate antimicrobial resistance. These results demonstrated that combinations that comprise cinnamaldehyde have noteworthy antimicrobial and anti-inflammatory properties which may warrant further investigation. Combining ibuprofen with conventional antimicrobials and essential oil compounds may also offer potential advantages in managing resistant infections through direct and indirect antimicrobial mechanisms.