Antibacterial activities of plant-based alkaloids and terpenoids

Alkaloids and terpenoids from plant extracts have enormous beneficial aspects and are commercially used in the form of oxygenated, hydrogenated and dehydrogenated derivatives (Cushnie, Cushnie & Lamb, 2014). However, they are also produced by different species of microorganisms and equally helps in antibacterial activities (Mabhiza, Chitemerere & Mukanganyama, 2016). Alkaloids and terpenoids produced by both microorganisms and plants have a similar impact on various harmful bacteria. Therefore, it is important to understand and explore the contrasting chemical and structural composition of different alkaloids and terpenoids found in plants and micro-organisms.

Antibacterial alkaloids from plants

Plant-based secondary metabolites with antibacterial properties were found in extracts from Thylachium africanum, Boscia angustifolia, Cissus quadrangularis, Grewia simi, Acacia etbaica, Scadoxus multiflorus, Commiphora africana and Acacia nilotica. However, methanol was the main chemical compound found from the extracts with the potential to act on Mycobacterium tuberculosis, Mycobacterium kansaii, Mycobacterium smegmatis, Mycobacterium fortuitum, S. typhi, K. pneumonia, P. aeruginosa, E. coli and S. aureus (Mariita et al., 2011).

Furthermore, a study by Nabavi et al., (2015) identified various species of Thymus spp. and the alkaloids extracts have an antibacterial impact on S. aureus (MRSA) and other standard bacterial strains (B. cereus ATCC 9634, E. coli ATCC 3428, Klebsiella pneumoniae ATCC 13883, S. aureus ATCC 25922, and S. aureus ATCC 33592). Secondary metabolites of alkaloids from Thymus spp. such as thymol, carvon, camphor, camphene, limonene, menthone, myrcene, and carvacrol were found to have antibacterial activities. The following list indicates the list of various alkaloid compounds from different plant species and their impact on different species of bacteria.

List of plant-based antibacterial alkaloids compounds (Cowan, 1999; Omojate Godstime et al., 2014)

Antibacterial terpenoids from plants

Terpenoids extracted from the bark of Psidium guajava was found with high concentrations of ethanol extract along with other phytochemicals exhibited anti-Streptococcus faecalis activity (Abdulhamid et al., 2014). Terpenoids from Morinda citifolia was also found to have anti-P. aeruginosa and S. epidermidis activities, whereas, Aspilia mossambicensis, Ocimum gratissimum, O. gratissimum, A. mossambicensis, T. asiatica and Toddalia asiatica were found to have antibacterial activity against methicillin-resistant S. aureus (MRSA) and P. aeruginosa (Compean & Ynalvez, 2014).

Nabavi et al., (2015) also found that Carvacrol an important terpenoid mostly found in plant species such as thyme, oregano, wild bergamot, as well as pepperwort have antibacterial activity on different forms of bacteria. In addition, Bouyahya et al., (2017) identified Cistus monspeliensis, Cistus albidus, Lavandula stoechas, Ajuga iva Daphne gnidium with antibacterial activity on S. aureus and E. coli; Arbutus unedo with terpenoids like n-hexane, ethyl acetate, methanolic and ethanolic extracts have impact on L. monocytogenes and P. aeruginosa; and Ficus carica has antibacterial potential on S. epidermidis.

Steps of bacterial pathogenicity by alkaloids and terpenoids

• Disruption of virulence gene regulation.
• Inhibition of sortase.
• Disruption of fimbriae and other adhesins.
• Inhibition of bacterial defences against the host immune system.
• Restriction of secretion systems.
• Inhibition of exotoxin-mediated effects.
• Restriction of destructive enzyme-mediated effects.
• Inhibition of biofilm formation.

Mechanism of antibacterial activities

Most alkaloids and terpenoids extracted from plants act through efflux pump inhibition and reach a sufficiently high intracellular concentration (Cushnie, Cushnie, & Lamb 2014). Furthermore, the downregulation and inhibition of efflux pump ATPases cause disruption of the ABC transporters in the bacterium and reduce oxygen consumption. This causes disruption of bacterial homeostasis and further compromises the outer membrane and cytoplasmic membrane integrity of the bacterium. At last, the series of inhibitions and disruptions causes leakage of cytoplasmic contents leading to anti-microbial activity.

However, Bazaka et al., (2015) argue that alkaloid and terpenoids interact with bacterial membrane, thereby, causing disruption through lipophilic products. Moreover, this leads to membrane expansion causing an increase of membrane fluidity and permeability. Furthermore, it causes disturbance of membrane-embedded proteins, inhibition of respiration, and alteration of ion transport processes in both Gram-positive and Gram-negative bacteria.

References

• Abdulhamid, A., Fakai, I. M., Sani, I., Argungu, A. U., & Bello, F. (2014). Preliminary phytochemical and antibacterial activity of ethanolic and aqueous stem bark of extracts of Psidium guajava. American Journal Drug Discovery Development, 4, 85-89.
• Bazaka, K., Jacob, M. V., Chrzanowski, W., & Ostrikov, K. (2015). Anti-bacterial surfaces: natural agents, mechanisms of action, and plasma surface modification. Rsc Advances, 5(60), 48739-48759.
• Bouyahya, A., Bakri, Y., Khay, E. O., Edaoudi, F., Talbaoui, A., Et-Touys, A., … & Dakka, N. (2017). Antibacterial, antioxidant and antitumor properties of Moroccan medicinal plants: a review. Asian Pac J Trop Dis, 7(1), 57-64.
• Compean, K. L., & Ynalvez, R. A. (2014). Antimicrobial activity of plant secondary metabolites: A review. Research Journal of Medicinal Plants, 8(5), 204-213.
• Cowan, M. M. (1999). Plant products as antimicrobial agents. Clinical microbiology reviews, 12(4), 564-582.
• Cushnie, T. T., Cushnie, B., & Lamb, A. J. (2014). Alkaloids: an overview of their antibacterial, antibiotic-enhancing and antivirulence activities. International Journal of Antimicrobial Agents, 44(5), 377-386.
• Mabhiza, D., Chitemerere, T. and Mukanganyama, S. (2016) ‘Antibacterial Properties of Alkaloid Extracts from Callistemon citrinus and Vernonia adoensis against Staphylococcus aureus and Pseudomonas aeruginosa’, International Journal of Medicinal Chemistry, 2016, pp. 1–7. doi: 10.1155/2016/6304163.
• Mariita, R. M., Ogol, C. K. P. O., Oguge, N. O., & Okemo, P. O. (2011). Methanol extract of Three medicinal plants from samburu in northern kenya show significant antimycobacterial, antibacterial and antifungal properties. Research Journal of Medicinal Plant, 5(1), 54-64.
• Nabavi, S. M., Marchese, A., Izadi, M., Curti, V., Daglia, M., & Nabavi, S. F. (2015). Plants belonging to the genus Thymus as antibacterial agents: From farm to pharmacy. Food Chemistry, 173, 339-347.
• Omojate Godstime, C., Enwa Felix, O., Jewo Augustina, O., & Eze Christopher, O. (2014). Mechanisms of antimicrobial actions of phytochemicals against enteric pathogens–a review. J Pharm Chem Biol Sci, 2(2), 77-85.