Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii
Abstract The use of natural products as antibiotic adjuvants to enhance efficacy and mitigate resistance is increasingly recognized as a promising strategy. This study explored five novel synergistic antimicrobial combinations (SACs) of carvacrol (CARV) and three already identified SACs of thymol (T...
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SpringerOpen
2025-06-01
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| Series: | Natural Products and Bioprospecting |
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| Online Access: | https://doi.org/10.1007/s13659-025-00518-7 |
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| author | Cristina Gan Elisa Langa Gang Wang Françoise Van Bambeke Diego Ballestero María Rosa Pino-Otín |
| author_facet | Cristina Gan Elisa Langa Gang Wang Françoise Van Bambeke Diego Ballestero María Rosa Pino-Otín |
| author_sort | Cristina Gan |
| collection | DOAJ |
| description | Abstract The use of natural products as antibiotic adjuvants to enhance efficacy and mitigate resistance is increasingly recognized as a promising strategy. This study explored five novel synergistic antimicrobial combinations (SACs) of carvacrol (CARV) and three already identified SACs of thymol (THY) with chloramphenicol, gentamicin, and streptomycin against Staphylococcus aureus and Acinetobacter baumannii, critical WHO-listed pathogens, and investigated their mechanisms of action and resistance-prevention capabilities. Despite being isomers, CARV and THY exhibited distinct synergistic effects and fractional inhibitory concentration index (FICI) values depending on the antibiotic and bacterial species. The SACs significantly reduced the required antibiotic dose by 4- to 16-fold, with FICI values ranging from 0.25 to 0.5. Growth kinetics revealed that SACs completely inhibited planktonic bacterial growth, outperforming antibiotics alone. Additionally, the SACs demonstrated efficacy in both inhibiting and eradicating biofilms of S. aureus and A. baumannii. Resistance development studies highlighted that neither THY nor CARV induced resistance in these pathogens. Moreover, SACs combining aminoglycosides with THY reduced the emergence of resistance in A. baumannii by up to 32-fold. In S. aureus, THY mitigated gentamicin resistance by 16-fold. CARV exhibited similar, albeit slightly less potent, effects. Mechanistic investigations revealed that THY and CARV exert antimicrobial action by multiple mechanisms, including bacterial membrane depolarization and disruption, efflux pump inhibition, disrupting ATP metabolism and mitigating oxidative stress induced by antibiotics. These findings highlight the potential of SACs to enhance antibiotic efficacy while preventing resistance, positioning them as strong candidates for innovative antimicrobial therapies against multidrug-resistant pathogens. Graphical Abstract |
| format | Article |
| id | doaj-art-9781230f1b2b4e06bd700be04075721d |
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| issn | 2192-2195 2192-2209 |
| language | English |
| publishDate | 2025-06-01 |
| publisher | SpringerOpen |
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| series | Natural Products and Bioprospecting |
| spelling | doaj-art-9781230f1b2b4e06bd700be04075721d2025-08-20T02:31:09ZengSpringerOpenNatural Products and Bioprospecting2192-21952192-22092025-06-0115112210.1007/s13659-025-00518-7Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumanniiCristina Gan0Elisa Langa1Gang Wang2Françoise Van Bambeke3Diego Ballestero4María Rosa Pino-Otín5Universidad San Jorge. Campus Universitario Villanueva de Gállego Autovía AUniversidad San Jorge. Campus Universitario Villanueva de Gállego Autovía ALouvain Drug Research Institute, Université Catholique de LouvainLouvain Drug Research Institute, Université Catholique de LouvainUniversidad San Jorge. Campus Universitario Villanueva de Gállego Autovía AUniversidad San Jorge. Campus Universitario Villanueva de Gállego Autovía AAbstract The use of natural products as antibiotic adjuvants to enhance efficacy and mitigate resistance is increasingly recognized as a promising strategy. This study explored five novel synergistic antimicrobial combinations (SACs) of carvacrol (CARV) and three already identified SACs of thymol (THY) with chloramphenicol, gentamicin, and streptomycin against Staphylococcus aureus and Acinetobacter baumannii, critical WHO-listed pathogens, and investigated their mechanisms of action and resistance-prevention capabilities. Despite being isomers, CARV and THY exhibited distinct synergistic effects and fractional inhibitory concentration index (FICI) values depending on the antibiotic and bacterial species. The SACs significantly reduced the required antibiotic dose by 4- to 16-fold, with FICI values ranging from 0.25 to 0.5. Growth kinetics revealed that SACs completely inhibited planktonic bacterial growth, outperforming antibiotics alone. Additionally, the SACs demonstrated efficacy in both inhibiting and eradicating biofilms of S. aureus and A. baumannii. Resistance development studies highlighted that neither THY nor CARV induced resistance in these pathogens. Moreover, SACs combining aminoglycosides with THY reduced the emergence of resistance in A. baumannii by up to 32-fold. In S. aureus, THY mitigated gentamicin resistance by 16-fold. CARV exhibited similar, albeit slightly less potent, effects. Mechanistic investigations revealed that THY and CARV exert antimicrobial action by multiple mechanisms, including bacterial membrane depolarization and disruption, efflux pump inhibition, disrupting ATP metabolism and mitigating oxidative stress induced by antibiotics. These findings highlight the potential of SACs to enhance antibiotic efficacy while preventing resistance, positioning them as strong candidates for innovative antimicrobial therapies against multidrug-resistant pathogens. Graphical Abstracthttps://doi.org/10.1007/s13659-025-00518-7ThymolCarvacrolStaphylococcus aureusAcinetobacter baumanniiAntibiotic resistance |
| spellingShingle | Cristina Gan Elisa Langa Gang Wang Françoise Van Bambeke Diego Ballestero María Rosa Pino-Otín Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii Natural Products and Bioprospecting Thymol Carvacrol Staphylococcus aureus Acinetobacter baumannii Antibiotic resistance |
| title | Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii |
| title_full | Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii |
| title_fullStr | Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii |
| title_full_unstemmed | Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii |
| title_short | Mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in Staphylococcus aureus and Acinetobacter baumannii |
| title_sort | mechanisms of action and resistance prevention of synergistic thymol and carvacrol combinations with antibiotics in staphylococcus aureus and acinetobacter baumannii |
| topic | Thymol Carvacrol Staphylococcus aureus Acinetobacter baumannii Antibiotic resistance |
| url | https://doi.org/10.1007/s13659-025-00518-7 |
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