Antibacterial, Bactericidal and Membrane-Disruptive Activities of Essential Oils from Callistemon salignus, Croton gratissimus and Melaleuca bracteata against Reference Enterococcus Species
Mona M. E. Eleiwa
Department of Biology, Ibn Sina National College for Medical Studies, P.O. Box 31906 Jeddah 21418, Al Mahjar, Saudi Arabia.
Sideeqot T. Abdullahi
Department of Microbiology, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria.
Omobolanle E. Oladapo
Department of Microbiology, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria and Department of Microbiology, Lagos State College of Nursing, Alimosho General Hospital complex, LASU/Isheri Road, Igando Lagos State, Nigeria.
Emmanuel E. Aduak
Department of Chemistry, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria.
Kanyinsola O. Akinkunmi
Department of Chemistry, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria.
Victoria A. Dada
Department of Chemistry, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria.
Kehinde O. Amisu
Department of Microbiology, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria.
Oladipupo A. Lawal *
Department of Chemistry, Lagos State University, PMB 0001 LASU Post Office, Ojo, Lagos, Nigeria and Department of Biochemistry& Microbiology, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, South Africa.
Andy R. Opoku
Department of Biochemistry& Microbiology, University of Zululand, Private Bag X1001, KwaDlangezwa 3886, South Africa.
*Author to whom correspondence should be addressed.
Abstract
The increasing occurrence of antimicrobial-resistant Enterococcus species has encouraged the investigation of plant-derived products with antibacterial potential. This study evaluated the antibacterial, bactericidal, and membrane-disruptive activities of essential oils obtained from the leaves of Callistemon salignus, Croton gratissimus, and Melaleuca bracteata against five reference Enterococcus species: Enterococcus avium, Enterococcus casseliflavus, Enterococcus hirae, Enterococcus gallinarum, and Enterococcus faecalis. Antibacterial activity was assessed by agar disc diffusion, while minimum inhibitory concentration and minimum bactericidal concentration values were determined using broth microdilution-based methods. Bactericidal potential was further interpreted using MBC/MIC ratios, and membrane-disruptive activity was evaluated using membrane-damage indices. All tested essential oils produced measurable inhibition against at least some of the Enterococcus species, with inhibition zones ranging from 9.0 to 12.0 mm, compared with 25 to 47 mm for ciprofloxacin. Melaleuca bracteata essential oil showed the strongest overall activity, with MIC values ranging from 2.5 to 5.0 mg/mL and MBC values of 5.0 to >5.0 mg/mL. Callistemon salignus showed moderate activity, with MIC values from 2.5 to >5.0 mg/mL and MBC values of 5.0 to >5.0 mg/mL. Croton gratissimus showed comparatively weaker activity, with MIC values of 5.0 to >5.0 mg/mL and no detectable bactericidal activity within the tested concentration range. Membrane-damage indices were highest for M. bracteata against E. avium and E. faecalis. Overall, the findings indicate that M. bracteata and C. salignus possess measurable antibacterial effects against reference Enterococcus species, with membrane disruption likely contributing to their activity.
Keywords: Callistemon salignus, Croton gratissimus, Melaleuca bracteata, essential oil, antibacterial, membrane disruptive, Enterococcus species.