Antibacterial activities of plant-based alkaloids and terpenoids

By Avishek Majumder on February 22, 2019

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.

Common types of alkaloids and thier chemical structures (Cowan, 1999)
Common types of alkaloids and thier chemical structures (Cowan, 1999)
Common types of terpenoids and thier chemical structures (Cowan, 1999)
Common types of terpenoids and thier chemical structures (Cowan, 1999)

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.

Plant speciesAlkaloid compoundsBacterial species
Berberis vulgarisBerberineBacteria
Piper nigrumPiperineLactobacillus, Micrococcus, E. coli, E. faecalis
Erythroxylum cocaCocaineGram-negative and -positive cocci
Gloriosa superbaColchicineBacteria
Hydrastis canadensisBacteria, Giardia duodenale, trypanosomes
Mahonia aquifolia BerberinePlasmodium
Carica papayaLatexBacteria
Vinca minorReserpineBacteria
Lophophora williamsiiMescalineBacteria
Papaver somniferumOpiumBacteria
Cinchona sp.QuininePlasmodium spp.
Rauvolfia serpentinaReserpineBacteria
Phyllanthus discoideus
Cinchona officinaliQuinolineBacteria
Clausena anisataCarbazoleBacteria
Tamarindus indicaEscherichia coli, Staphylococcus aureus, Salmonella typhi and Pseudomonas aeruginosa
Zapoteca portoricensisE. coli, S. aureus, Streptococcus pyogenes, Klebsiella pneumonia and P. aeruginosa
Thymus algeriensisCarvacrolBacteria
Thymus vulgarisLinaloolGram positive 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.

Plant speciesAlkaloid compoundsBacterial species
Ocimum basilicumEssential oilSalmonella, bacteria
Laurus nobilisEssential oilBacteria
Schinus terebinthifoliusTerebinthoneBacteria
Barosma setulinaEssential oilBacteria
Arctium lappaEssential oilBacteria
Cinnamomum verumEssential oilsBacteria
Capsicum annuumCapsaicinBacteria
Syzygium aromaticumEugenolBacteria
Anethum graveolensEssential oilsBacteria
Eucalyptus globulusTanninBacteria
Allium sativumAllicin, ajoeneBacteria
Centella asiaticaAsiatocosideM. leprae
Humulus lupulusLupulone, humuloneBacteria
Armoracia rusticanaLupuloneBacteria
Carica papayaLatexBacteria
Mentha piperitaMentholBacteria
Rosmarinus officinalisEssential oilsBacteria
Satureja montanaCarvacrolBacteria
Tanacetum vulgareEssential oilsBacteria
Thymus vulgarisCaffeic acidBacteria
Curcuma longaCurcuminBacteria
Valeriana officinalisEssential oilsBacteria
Salix albaEssential oilsBacteria
Jacaranda mimosifoliaEssential oilsPseudomonas aeruginosa

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.

Mechanism of alkaloids and terpenoids in antibacterial activities (Bazaka et al., 2015)
Mechanism of alkaloids and terpenoids in antibacterial activities (Bazaka et al., 2015)

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.


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Avishek Majumder