Exploring the therapeutic potential of Ocimum gratissimum extracts against microbial infections: A Comprehensive review

Insect and mosquito repellent

O. gratissimum contains larvicide, which inhibits an insect’s growth at the larval life stage. Commonly found products of these larvicidal are camphor, cineole, and limonene. These leaves and others serve as a natural repellent for mosquitoes, houseflies, bugs, and other crawling and flying insects (Kin et al., 2018; Ojewumi et al., 2017a; 2018a; b).^[24-27]

Anti-inflammatory properties

O. gratissimum has some anti-inflammatory properties that can be used in pain relief drugs, such as Ibuprofen and aspirin. When these leaves are extracted, it is discovered that it is an effective cure for ulcer pains, ear infections, fever, etc. (Amengialue et al., 2013; Okoye et al., 2014; Babatunde et al., 2019).^[28-30]

Treatment of respiratory disorders

Fluid extracts of leaves effectively affect markers of irritation, including kinases in protein, interleukins, and leukocytes/eosinophils in the experimental respiratory hypersensitivity models (in vitro tries assessing impacts on aviation route epithelial cells, in vivo examinations in rodents) and along these lines can be utilized in overseeing breathing issues (Jiao et al., 2013).^[31]

Reduce blood level

They contain cinnamic acid, which aids in improving circulation and regulation of blood sugar levels, and can also be used in improving the breathing sequence of an individual with respiratory problems (Abhay et al., 2014).^[32]

Remedy for stomach disorders

This leaf has been found to take care of stomach upset, including gastroenteritis; just by mere chewing, the leaf can cure cold or flu symptoms. Boiling these leaves with the addition of ginger and honey is effective for treating cough, fever, asthma, bronchitis, and influenza. Drinking from squeezed leaves would help with stooling (Okoye et al., 2014).^[29]

Antispasmodic effect

Aqueous extract from the leaf has an antispasmodic effect used to treat ailments such as convulsions and seizures. This extract, when boiled, can be taken as a tonic and, when gargled, could help with sore throat (Orafidiya et al., 2004).^[33]

Antimicrobial and antibacterial properties

The antimicrobial and antibacterial property of the leaf enables it to be used as a food preservative. The antimicrobial properties make it possible for it to be used to treat infections such as tooth decay, mouth infections, oral infections, fungal infections, and bad breath. Studies also show that O. gratissimum has antibacterial properties against Salmonella Enteritidis, Staphylococcus aureus, and Escherichia coli (Nakamura et al., 1999; Ojewumi et al., 2021c).^[34,35]

Fight against sickle cell anemia

Due to the anti-sickling properties of ursolic acid found in O. gratissimum, the compound fights against the production of abnormal, sickle-shaped red blood cells (Tshilanda et al., 2015).^[36]

Protect from cardiovascular diseases

Heart-friendly compounds in the leaf, such as magnesium, are good for lowering cholesterol levels and aids blood circulation. According to Li et al., 2012^[37] water extract of O. gratissimum reduced the effect of induced cardiac abnormalities linked with liver fibrosis in rats. It was also revealed that scent leaf extract could help protect and reverse toxicity and blood pressure changes linked with exposure to cobalt-chloride in rats.

Supercritical CO₂ method of extraction

Supercritical CO₂ extraction is one of the most recent ways of extracting oils from potential plant parts; although not cost-effective, it yields good oil quality. CO₂ becomes supercritical at 33°C, which is neither gas nor liquid; instead, it possesses gas and liquid properties. Since CO₂ is inert, it does not chemically interact with the oil produced.

Steam distillation extraction method

Steam distillation is another good technique used to extract oils from various plant parts, where the potential plant is put in a container and steam is forced over it. When heated up, the steam assists with delivering the aromatic organic atoms from the plant since the steam powers open up the jackets wherein the oils are kept.

Water distillation extraction method

The water distillation extraction method is known to be one of the oldest extraction methods [Figure 1]. It is the most suitable method for fresh and dry plant samples; heat does not damage them. This method is carried out by heating water at the top of the vessel at the same position where the plant is placed. The EO is usually transported by vapor and accumulates in water due to the difference in density when it gets to the collecting vessel called “The Florentine Container.”

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Figure 1:

Steam and water distillation method. Source: (Akdağ and Öztürk, 2018).^[60]

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Microwave-assisted hydrodistillation extraction method (MAHD)

MAHD is a more advanced method used in the extraction of crude oils from various plant parts [Figure 2] (Golmakani and Rezaei, 2008; Filly et al., 2014).^[41,42] The production of high-yield and good-quality EOs, shorter extraction time, and faster extraction rate with fewer solvents have been associated with this method.

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Figure 2:

Microwave extraction method. Tshilanda, 2015^[36]

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Maceration

The maceration extraction method is used in the wine-making process and is now adopted and used for medicinal plant research. The maceration method involves soaking the plant sample, whether powdered or coarse, in a jar with a solvent and kept at ambient temperature for three days with regular agitation (Organization et al., 2008).^[43] The aim is to soften and open the plant walls to release soluble phytochemicals. It is then strained using the filtration method after 3 days.

Mentha spicata (spearmint)

Mentha spicata is a rhizomatous, herbaceous, and perennial plant of about 35–100 cm tall, with hairy to hair less hair tall stems, underground fleshy wide-spreading rhizome with medium-sized leaves. (Ojewumi et al., 2017a).^[25]

Both freshly plucked and dried plants are frequently used in the food, cosmetic, and pharmaceutical industries (Bensabah et al., 2013).^[44] Having strong antioxidant properties, these plants are a rich source of polyphenols. Plate 2 shows the stem with leaves of a scent leave.

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Plate 2:

Scent leave (Source: Ojewumi et al., 2017a).^[25]

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Moringa oleifera

Moringa oleifera belongs to the Moringaceae family. Since this plant possesses various amazing healing properties, it is widely known as “Miracle Tree” (Ojewumi et al., 2018a).^[26] Due to its various applications, isolation of its bioactive constituents from different parts of the leaf is usually carried out (Guevara et al., 1999).^[45]

Secondary metabolites

Mg

It can be administered intravenously to decrease the chance of atrial fibrillation and also to helps regulate heart rhythm (Holleman et al., 1988).^[53] In the experiment carried out by Alexander (2016),^[54] magnesium was discovered to be one of the most abundant elements with a 1.712 ± 0.537 mg/kg concentration.

Na

The role of this element is to maintain the fluid balance within body cells and in the proper functioning of both muscles and nerve impulses. Milbury and Richer, in 2008,^[55] reported that an average adult needs about 3–4 g daily Na, but modern dietary habits take in 6–20 g daily.

Ca

The role of calcium is to maintain strong teeth and bone, more significant parts of human blood and extracellular fluids also need lots of calcium (Holleman et al., 1988).^[53]

Fe

Iron in plants shows that they are essential for the transportation of oxygen and the production of red blood cells in the body (Bahl and Bahl, 2006).^[56]

Cu

In addition to energy metabolism, another function of copper is the release of iron from cells into the body’s plasma (Bahl and Bahl, 2006).^[56]

Staphylococcus aureus

S. aureus is a Gram-positive pathogen for both animals and humans, causing various degrees of diseases ranging from severe diseases such as endocarditis, bacteremia, pneumonia, and septic arthritis to superficial skin infections. S. aureus is of the family Staphylococcaceae. Mammalian species, including human beings, are most affected. S. aureus is easily transmitted due to its wide species range, including transmission between humans and animals (Spaulding et al., 2013).^[57] Plate 3 shows a cross-sectional picture of S. aureus.

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Plate 3:

Staphylococcus aureus (Source: Spaulding et al., 2013).^[57]

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Streptococcus pneumoniae

S. pneumoniae is a Gram-positive bacterium which is the cause of the majority of community-acquired pneumonia. This organism is located in the human respiratory tract, showing a symbiosis relationship with humans. Nevertheless, infection by pneumococcus is not only dangerous, causing pneumonia, but also causes otitis media, bronchitis, meningitis, and septicemia. The alpha-hemolytic property of S. pneumoniae means that red blood cells can be broken down by producing hydrogen peroxide (H₂O₂) (van der Poll and Opal, 2009).^[58] Plate 4 shows a cross-sectional picture of S. pneumoniae.

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Plate 4:

Streptococcus pneumoniae (Source: van der Poll and Opal, 2009).^[58]

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Escherichia coli

E. coli is a type of bacteria that is popularly found in the intestines. Most of these types of E. coli are not harmful and can even help digestion processes. They are also primarily responsible for food poisoning in their hosts, commonly found in fecaloid matter. It is frequently found in fecaloid matter (Kotloff et al., 2013).^[59] E. coli causes urinary tract infections and Pneumonia from different types of bacteria. About 75–95% of urinary tract infections are caused by this bacterium. Shiga [toxin-producing E-coli] is a toxin caused by E.coli that makes a person sick, damaging the intestine lining. A much-known bad strain is 0157:H7, which causes severe sickness, vomiting, bloody diarrhea, and abdominal pains. One can get infected by E. coli through untreated milk, vegetables, ground meat and fruit, other food, beverages, water, other people, and animals. Plate 5 shows a cross-sectional picture of E. coli.

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Plate 5:

Escherichia coli (Source: Kotloff et al., 2013).^[59]

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Salmonella typhimurium

This organism can cause contamination in any living thing. It is regularly related to the consumption of animal products. S. Typhimurium can move people through crude or half-cooked contaminated food, such as eggs and meat. In poultry, S. Typhimurium is passed from flying creatures like birds to birds, mostly through droppings. When they are butchered for eating, the microbes move from their gut to the fleshy parts of their body and can likewise be transferred from the winged creature’s ovaries to their eggs. S. Typhimurium causes gastroenteritis (aggravation of the gut part), prompting stomach cramps and fever. These side effects may last as long as 7 days. Notwithstanding, anti-infection agents or different medicines might be required if individuals cannot ward off the disease themselves due to a fundamental condition, such as a compromised immune system. Plate 6 shows a cross-sectional picture of S. Typhimurium.

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Plate 6:

Salmonella yphimurium (Source: Nakamura et al., 1999).^[34]

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Salmonella typhi

S. typhi affects only cause diseases in human beings, for example, typhoid fever. It is widespread in some developing countries with poor hygiene and sewage-contaminated water. Typhoid fever symptoms include loss of appetite, tiredness, and stomach pains. In the absence of immediate treatment, S. typhi infection may lead to liver damage, internal bleeding, holes in the gut, and typhoid fever. Typhoid can be fatal in up to 20% if not treated appropriately. Stool and blood samples are ways typhoid can be diagnosed. S. typhi is carried in the blood of people with this typhoid, and the bacteria are passed out in their blood or feces. Vaccination is recommended when traveling to a country where typhoid is rampant. Plate 7 shows a cross-sectional picture of S, Typhi.

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Plate 7:

Salmonella typhi (Source: Nakamura et al., 1999).^[34]

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Klebsiella pneumonia

K. pneumoniae is bacteria that naturally live in the intestine and feces. The bacteria are not threatening when inside the intestine but can be threatening when they spread to other organs, leading to severe problems. Part of the body K. pneumonia can affect the bladder, brain, liver, eyes, blood, and wounds. When the immune system is weak, conditions caused by long-term antibiotic use increase the chances of getting this infection. Plate 8 shows a cross-sectional picture of K. pneumonia.

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Plate 8:

Klebsiella pneumonia (Source: Korvick et al., 1991).^[83]

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O. gratissimum extract antibacterial activity

Kolawole, et al. (2018)^[76] reported that O. gratissimum had a higher antibacterial effect compared to that of V. amygdalina and also phytonutrients (alkaloids, flavonoid, tannin, and steroid) compared with the extract obtained from the leaf of V. amygdalina. The antimicrobial property of O. gratissimum exhibited a higher zone of inhibition on the tested organisms.

Consequently, it is essential to look for alternative sources of antibiotics since the pathogenic microbes are beginning to develop resistance against antibiotics (Agarwal et al., 2012).^[77]

Various plant extracts have been discovered to possess healing properties. These properties provide bactericidal and bacteriostatic effects on bacteria (Effraim et al., 2000; Alo et al., 2012).^[80,81] The results showed that cold water extract of V. amygdalina showed inhibition zone diameter (15 mm) only against S. typhi, which supports the research of Ogbulie et al. (2007).^[82] Likewise, the hot water of V. amygdalina restrained the growth of E. coli and S. typhi with the diameter (15 and 20 mm), respectively, which tallies with the findings of Ogbulie et al., 2007.^[82] Ethanolic extract held back the growth of E. coli and S. typhi with the inhibition zone diameter of 23 and 13 mm, respectively, and it is related to the research findings of Ogbulie et al., 2007.^[82] Furthermore, it was documented by Okigbo and Mmeka (2008)^[84] that the V. amygdalina’s ethanolic and aqueous extract was able to inhibit that E. coli (Madubunyi et al., 1995)^[85] confirmed but opposed to (Ashebir and Ashenafi, 1999)^[86] on the observation on plants capability to inhibit E. coli. The methanolic extract of V. amygdalina suppressed/inhibited the growth of E. coli and S. typhi with the diameter inhibition zone (23 and 20 mm), supporting Akinpelu’s (1999)^[87] research that states that V. amygdalina leaf of 60% was potent at 25 mg/mL against E. coli and S. typhi isolates. However, in this experiment, V. amygdalina showed no inhibition growth against K. pneumonia. Subsequently, O. gratissimum, cold water extract did not inhibit the growth of all the tested organisms, while only inhibiting the growth of E. coli with the zone of inhibition diameter (120 mm), which negates the research done by (Adebolu and Oladimeji, 2005).^[11] Thus, O. gratissimum inhibited S. typhi and E. coli with inhibition zone diameters of 20 m m and 21 mm, respectively [Plate 9], which supports the research work of (Nwinyi et al., 2018)^[88] that reported that ethanol extracts of O. gratissimum have a higher antibacterial activity against E. coli. Moreover, the methanolic extract of O. gratissimum only inhibited S. typhi with an inhibition zone diameter (23 mm). Hence, O. gratissimum did not inhibit the growth of K. pneumoniae. Furthermore, Ogbulie et al. (2007)^[82] research negates that the cold and hot water extracts of A. malagueta only inhibited the growth of E. coli at 19 mm and 21 mm, respectively. At the same time, the ethanolic extract of A. malagueta could only inhibit the growth of S. typhi with the inhibition zone diameter at 14 mm, contrary to Ogbulie et al., 2007^[82] findings. E. coli was only inhibited in the methanolic extracts with an inhibition zone diameter of 12 mm. In conclusion, no plant extracts from this research could inhibit the growth of K. pneumoniae.

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Plate 9:

Antibacterial activity on Escherichia coli (Source: Kin et al., 2018).^[24]

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Akinyemi et al. (2005)^[79] carried out an extensive test on the stem bark parts. Stem back extract showed antimicrobial properties to both ethanolic and aqueous extract of O. gratissimum. At lower concentrations, they function as bacteriostatic, and at higher concentrations, as bactericidal. The minimum inhibitory concentration and minimal concentration of bactericides were discovered to be between 18.2–24.0 g/mL and 30.4–37.0 μg/mL, respectively. In other words, their results offer a scientific basis for the traditional use of water and ethanol extracts of O. gratissimum against Methicillin-resistant S. aureus associated diseases (Akinyemi et al., 2005; Nakamura et al., 1999).^[34,79]