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REVIEW ARTICLE
Year : 2023 | Volume
: 13
| Issue : 2 | Page : 45-59
Antimicrobial activities of Acacia genus: A review
Deeksha Adhikari1, Naresh Kumar Rangra2
1 Department of Pharmacognosy, ISF College of Pharmacy, Moga, Punjab 142001, India
2 Department of Pharmaceutical Chemistry & Analysis, ISF College of Pharmacy, Moga, Punjab 142001, India
Correspondence Address:
Naresh Kumar Rangra
Department of Pharmaceutical Chemistry & Analysis, ISF College of Pharmacy, Moga, Punjab 142001
India
Source of Support: None, Conflict of Interest: None
DOI: 10.4103/2221-1691.369609
More than 1300 species of the vast genus Acacia are found in tropical habitats. They are crucial economic plants since they produce traditional medicines, timber, and gum. The pharmacological uses of the Acacia genus include anti-diarrheal, anti-malarial, chronic pain relief, wound healing, anti-cancer, anti-rheumatism, and anti-diabetes activities. It is also used for treating various illnesses such as gastroenteritis, allergies, Alzheimer's disease, cough, and cardiovascular disease. The present review aims to summarize the antimicrobial activities including the antibacterial and antifungal activity of the Acacia genus. The literature was searched in books and online databases including SciFinder, Google Scholar, Scopus, PubMed, and scientific journals using the most relevant keywords: Acacia+antimicrobial, Acacia+antibacterial, and Acacia+antifungal.
Keywords: Acacia; Antimicrobial; Antibacterial; Antifungal; Polyphenols; Flavonoids
Since ancient times, it is well evidenced that plants are potential medicinal sources and are widely used in Ayurvedic, Unani, Chinese, and other medical systems[1]. Humans have relied on nature for thousands of years to encounter their basic health necessities, specifically for the usage of a variety of ailments[2]. Before the development of modern medicine, plants served as medicines in traditional medicinal systems, moreover, more than 60% of people worldwide use them today[3]. According to the latest numbers, more than a thousand plant species have been utilized either in their raw form or in their structured form as crude extracts in diverse cultures[4].
The Acacia species are typically called the wattles in Australia and thorn trees in Africa. They are crucial economic plants because they produce traditional medicines, wood, gum, tannins, and gum arabic. Many cultures have historically employed the bark, flowers, leaves, pods, seeds, and roots of Acacia to treat a variety of illnesses[5],[6]. Because many kinds of Acacia trees, particularly those that grow in arid climates, have spines and thus are called “thorn trees”. These can also be branches that have grown to be short, harsh, and acrid[7]. The genus Acacia is widely dispersed throughout the world, with communities in North and South America, Africa, and the Australia-Pacific region[8].
The plant Acacia belongs to the tribe Acacieae, which is part of the Fabaceae family subfamily Mimosoideae. About 1300 different species of the herb Acacia can be found throughout the world and also there is potential therapeutic use of Acacia species in both diet and ethnopharmacology. Acacia is found over the whole tropical world, primarily discovered in dry environments, including savannas, forests, and temperate, subtropical, and tropical regions. Moreover, this tropical grassland is a massive genus of woody, legumes, pod-bearing shrubs, and trees[9],[10]. Due to its resistance to drought, capacity to improve soil through nitrogen fixation, fodder as well as for shade and live fence, the genus Acacia is rapidly gaining appeal[11]. Since ancient times, various forms of healing have been accomplished using plants and plant extracts. In traditional medicine, the genus Acacia is used to relieve inflammation and pain[12],[13].
The primary goal of this review is to summarize the antimicrobial activities reported in the Acacia genus to date. The relevant literature was searched using the most specific keywords as“Acacia+antimicrobial”, “Acacia+antibacterial”, and “Acacia+antifungal”. Various offline and online electronic databases were used such as books, SciFinder, PubMed, Scopus, and Google Scholar for the preparation of this manuscript. The flowchart of literature screening is shown in [Figure 1].
1.1. Traditional uses of Acacia genus
Due to their adaptability and accessibility, Acacia has a very long history. It has been said that the ancient Egyptians employed a variety of Acacia species to treat a range of ailments, including internal bleeding, diarrhea, and skin conditions[14]. In sub- Saharan[15], Chinese[16], and Asian traditional medicine, for example in Ayurvedic (Indian) and Unani (Greco-Arabic)[17], Acacia genus is also quite prevalent. The phytoconstituents present in the Acacia with strong free radical scavenging and antioxidant properties are responsible for some pharmacological and biological properties, including antibacterial, anti-inflammatory, anti-hypertensive, antiplatelet, hypoglycemic, anti-atherosclerotic, and analgesic activities[18].
1.2. Pharmacological properties of Acacia genus
The most vital component to eradicate the uncertainty regarding the use of medicinal plants as medications for adjunct medicine is the fact that pharmacological action is primarily based on experience. However, the possible ethnopharmacological properties of Acacia species in diverse traditional systems of medicine, particularly those of Africa and Asia, where herbal pharmacopeia are mainly lacking, justify the verification demand for reliable and safe usage of Acacia genus. A variety of conditions, including diarrhea, Alzheimer’s disease, gastroenteritis, wounds, malaria, allergies, coughs, diabetes, cardiovascular disorders, chronic pain, and inflammatory illnesses like rheumatism and cancer, are among the many conditions for which traditional uses of Acacia species were generally supported by modern pharmacological studies[4].
1.3. Phytochemicals reported in Acacia genus
Acacia is a rich source of a wide range of chemical compounds[10]. The diverse genus Acacia contains several bioactive substances, including alkaloids (phenethylamine, amphetamine, candicine, mescaline, trichocereine, and hordenine)[19]; cyanogenic glycosides (linamarin, procacipetalin, heterodendrin, prunasin, sambunigrin, and lotaustralin); flavonoids (epicatechin, robinetinidol, fasciculiferin, melacacidin, galangin, myricetin, chrysin, and apigenin)[20]; terpenoids (acaciaside A&B and acacigenin)[21], phenolic compounds (ellagic acid, ferulic acid, and gallic acid) and tannins (gallotannin)[22],[23]. Over the past seven decades, 152 active ingredients have been found in the Acacia genus and the medicinal compounds are mainly present in the pods, root, bark, and leaves of the Acacia shrubs. Numerous other compounds such as flavonol and flavone glycosides, as well as aglycones, flavan-3-ols, flavan-3,4-diols, kaempferol-3 acid, quercetin, amyrin, glucoside isoquercetin sitosterol, and botulin were also found in various species of Acacia[24],[25]. Several secondary metabolites from medicinal plants from multiple nations were evaluated on how well they could inhibit a wide range of infectious microorganisms and these metabolites exhibit antibacterial action both in vivo and in vitro[26],[27].
Symbiotic relationships between medicinal plants and the microorganisms that are vital to plant health enable the production of a variety of biologically active chemicals. It is known that medicinal plants with antibacterial properties encourage the growth of endophytic bacteria that are more hostile to human pathogens[28],[29]. Further research on plant-based antimicrobials is urgently required because they offer a major unexplored supply of medications. Antimicrobials produced from plants with immense medicinal potential have a long history of offering desperately needed new treatments[30].
2. Antibacterial activity of Acacia genusThe most commonly mentioned pharmacological action of Acacia species is its antimicrobial properties. While Acacia plants were used as antimicrobial agents extensively in folklore medicine, the abundance of written work is likely a result of how easy and inexpensive it is to conduct antibacterial and antifungal studies. The minimum inhibitory concentration (MIC) in liquid culture media and zone of inhibition (ZOI) in solid culture media are typically used to express antimicrobial activity. To evaluate the antibacterial efficacy quantitatively, MIC is a more often used metric[31].
Before the development of current antibiotics, herbal remedies were used to treat microbiological infections. Numerous medicinal plants have been proven successful in treating bacterial illnesses[32]. Plants are a rich source of antibacterial drugs, due to a wide range of bioactive substances that plants produce, which are most likely established as a chemical defense against disease or predation[33]. Here, the antibacterial activity of various Acacia species has been discussed below.
2.1. Disc diffusion method-based antibacterial activities of Acacia genus
Arias et al. reported the antibacterial activity of Acacia aroma ethanolic and aqueous extracts from different parts (leaves, flowers, and stems) against Gram-positive bacteria [Enterococcus faecalis (E. faecalis), Staphylococcus aureus (S. aureus), S. aureus ATCC 29213, coagulase-negative staphylococci, Streptococcus agalactiae, Streptococcus pyogenes (S. pyogenes), E. faecalis ATCC 29212] as well as Gram-negative bacteria [Escherichia coli (E. coli), Klebsiella pneumoniae (K. pneumoniae), Proteus mirabilis (P. mirabilis), Enterobacter cloacae (E. cloacae), Serratia marcescens (S. marcescens), Morganella morganii, Acinetobacter baumannii, Pseudomonas aeruginosa (P. aeruginosa), Stenotrophomonas maltophilia, E. coli ATCC 35218, P. aeruginosa ATCC 27853, E. coli ATCC 25922] using disk diffusion method. Each ethanolic extract was found active against Gram-positive bacteria while only leaf and flower extracts were found active against Gram-negative bacteria[34].
Different extracts from Acacia arabica (A. arabica) leaf were analyzed for their antibacterial activities against various bacterial strains [E. coli, S. aureus, K. pneumoniae, Proteus vulgaris (P. vulgaris), Salmonella typhi (S. typhi), Shigella flexneri, Salmonella paratyphi (S. paratyphi), Salmonella typhimurium (S. typhimurium), P. aeruginosa, Enterobacter aerogenes (E. aerogenes)]. Among these extracts, the methanol extract of A. arabica showed the most potent results with ZOI of 22, 25, 22, 18, 26, 15, 23, 17, 20, and 24 mm for E. coli, S. aureus, E. aerogenes, P. aeruginosa, S. typhi, S. typhimurium, P. vulgaris, K. pneumoniae, S. paratyphi, and Shigella flexneri, respectively[35]. In another study, the antibacterial activity of Acacia berlandieri and Acacia rigidula leaf extracts (acetone, methanol, and acetic acid) was evaluated against numerous bacterial strains (Yersinia enterocolitica, E. coli, S. aureus, Providencia alcalifaciens, E. aerogenes, S. marcescens, K. pneumoniae, P. aeruginosa, and E. faecalis) using disc diffusion method. Based on the mean zones of inhibition, the antibacterial activity of both Acacia species differs from each other. Three of the nine bacterial species (Providencia alcalifaciens, P. aeruginosa, and Yersinia enterocolitica) were resistant to Acacia berlandieri with MIC of 6.00-8.99 mm. However, the extracts of Acacia rigidula were effective against the six bacterial species, and out of the six bacterial species, four were Gram-negative (Providencia alcalifaciens, P. aeruginosa, Yersinia enterocolitica, and E. coli) and two were Gram-positive (S. aureus and E. faecalis) with mean ZOI ranging from 8.70 to 17.56 mm for acetone extract, 7.80-14.43 mm for methanol extract and 6.00-12.33 mm for acetic acid extract[36].
In a study by Saini et al., five different species of Acacia species were investigated, including Acacia nilotica (A. nilotica), Acacia catechu (A. catechu), Acacia senegal (A. senegal), Acacia tortilis (A. tortilis), and Acacia jacquemontii for antibacterial activity. A. catechu and A. nilotica showed the most potent activity toward three bacteria (E. coli, S. aureus, and S. typhi). Among these species, methanolic extracts of the plant A. nilotica (pods) and A. catechu (bark) were reported to be the most effective. The methanolic extract of A. nilotica (pods) demonstrated significant activity against E. coli, whereas A. catechu showed noteworthy activity against S. aureus. The A. nilotica n-hexane extract, on the other hand, was also discovered to be particularly effective against S. typhi. In contrast, Acacia jacquemontii showed the lowest antibacterial activity[37].
Mutai et al. tested the antibacterial activity of (20S)-oxolupane-30-al, (20R)-oxolupane-30-al, and betulinic acid isolated from stem bark of Acacia mellifera against S. aureus ATCC 25923, E. coli ATCC 25922, and E. faecalis. At a concentration of 1 mg/mL, (20S)-oxolupane-30-al, (20R)-oxolupane-30-al, and betulinic acid demonstrated antibacterial action against S. aureus ATCC 25923 with ZOI of 10, 10, and 9 mm, respectively. However, no antibacterial effect on E. coli ATCC 25922 and E. faecalis was observed[38].
In a previous study, Ntshanka et al. used the ethanol, methanol, acetone, and chloroform extracts of Acacia mearnsii (A. mearnsii) leaf to assess their antibacterial properties against Gram-positive bacteria such as (S. aureus and E. faecalis) as well as Gram-negative bacteria such as (P. aeruginosa and E. coli). According to their results, A. mearnsii ethanol and methanol extracts displayed maximum activity, with 23 mm ZOI against P. aeruginosa whereas A. mearnsii ethanol and chloroform leaf extracts showed antibacterial activity against P. aeruginosa and E. faecalis, with concentrations of 39.06 and 78.13 mg/mL, respectively[39].
Amoussa et al. revealed the antibacterial activity of betulinic acid-3-trans-caffeate isolated from Acacia ataxacantha bark against various bacterial strains such as [S. aureus ATCC 6538, Staphylococcus epidermidis (S. epidermidis) CIP 8039, E. faecalis ATCC 29212, methicillin resistant S. aureus and P. aeruginosa CIP 82118], with ZOI of 15.7 to 23.3 mm. This compound showed the most significant inhibition against S. epidermidis, with an inhibition diameter of 23.3 mm. However, P. aeruginosa (Gramnegative bacteria) had intermediate sensitivity to betulinic acid-3-trans-caffeate, whereas Gram-positive bacteria displayed increased susceptibility. The MIC value for the investigated compounds varied from 12.5 to 50 µg/mL, indicating moderate antibacterial activity. The betulinic acid-3-trans-caffeate was active with the MIC and MBC values of 25 µg/mL against S. aureus and P. aeruginosa. In contrast, the MIC and MBC values against methicillin-resitant S. aureus and E. faecalis were observed as 50 µg/mL. This compound showed the lowest MIC value of 12.5 µg/mL against S. epidermidis[40]. Gum acacia from Omani and Sudan was tested for antibacterial activity using various extracts (hexane, chloroform, ethyl acetate, butanol, and water) against some bacterial strains (S. aureus Code No. 659, E. coli Code No. 846, E. coli Code No. 683 and K. pneumoniae Code No. 684). The highest activity against K. pneumoniae Code No. 684 was found in the chloroform extract at all concentrations (0.25, 0.5, 1, and 2 mg/mL) from Sudanese Gum acacia, and the lowest activity against S. aureus Code No. 659 was found in the n-butanol extract at all concentrations from the same source[41]. The antibacterial potential of Acacia polyacantha bark methanolic extract against Bacillus subtilis (B. subtilis), S. aureus, E. coli, and P. aeruginosa was investigated. At a higher concentration of 100 mg/mL, the highest activity was (19.00±0.05) mm against E. coli while at a lower concentration of 12.5 mg/mL, the lowest activity (10.3±0.1) mm against B. subtilis. S. aureus was affected at a concentration of 100 mg/mL with (13.6±0.02) mm ZOI. As a result, compared to the standard antibiotic, amoxicillin, Acacia polyacantha bark extract at 100 mg/mL showed a greater ZOI against E. coli, P. aeruginosa, and B. subtilis[42]. Methanolic extract of Acacia caesia stem was analyzed for the antibacterial activity against E. coli (ATCC 25922), S. aureus (ATCC 25923), and P. aeruginosa (ATCC 27853). The extract did not affect these microorganisms at a concentration of 25 µL. However, at a concentration of 100 µL, it displayed substantial activity comparable to that of ciprofloxacin. The ZOI of ciprofloxacin and the methanolic extract against E. coli was 30 mm and 17 mm, respectively. On the other hand, ZOI of 34 mm and 11 mm against S. aureus was observed for ciprofloxacin and the methanolic extract, respectively[43]. The summary of the above-mentioned antibacterial activities of Acacia genus is given in [Table 1].
Table 1: The antibacterial activity of Acacia species using disc diffusion method.2.2. Agar diffusion method-based antibacterial activities of Acacia genus
The n-hexane, ethyl acetate, ethanolic and methanolic extracts of Acacia mellifera were examined to verify the antibacterial activity against Gram-positive [Streptococcus pneumoniae (S. pneumoniae) ATCC 10341 and S. aureus ATCC 25923] and Gram-negative (K. pneumoniae ATCC 10273 and E. coli ATCC 25922) bacteria using agar dilution and broth macro dilution method. The n-hexane and ethanol extracts showed varying inhibition against S. pneumoniae ATCC 10341, S. aureus ATCC 25923 and E. coli ATCC 25922 while the ethyl acetate extract only showed the inhibitory action against S. pneumoniae ATCC10341 and E. coli ATCC 25922[44].
Okoro et al. analyzed the antibacterial action of different extracts from A. senegal stem bark against S. aureus, E. coli, S. pneumoniae, S. pyogenes, P. aeruginosa, P. vulgaris, S. typhi, and Shigella dysenteriae. The ZOI of ethanolic extract was 8, 8, and 8 mm for E. coli, P. aeruginosa, and S. typhi respectively at 500 µg/mL whereas the methanolic extract showed 8, 8, 8, 8, 8, and 10 mm for E. coli, K. pneumoniae, P. aeruginosa, P. vulgaris, S. typhi, and Shigella dysenteriae, respectively at 500 µg/mL. Furthermore, the MIC and MBC for the ethanol and methanol extracts were observed at 50 mg/mL and 400 mg/mL[45]. A. catechu methanolic extract was found active against some pathogenic and non-pathogenic species (B. subtilis, S. aureus, S. typhi, E. coli, and P. aeruginosa). Aqueous extracts consistently had lower antibacterial activity than extracts made in organic solvents. Further research revealed that methanol extracts showed more inhibitory activities with ZOI of 18 to 22 mm, compared with other extracts[46].
The antibacterial activity of A. nilotica methanolic fruit extract was determined against clinical isolates of five Gram-negative bacteria (E. coli, Shigella flexneri, S. typhi, P. aeruginosa, and K. pneumoniae), and two Gram-positive bacteria [Listeria monocytogenes and Bacillus cereus (B. cereus)]. Most of the studied microorganisms were inhibited by the fruit methanolic extract, with ZOI ranging from 11 to 39 mm. The highest ZOI was found against S. typhi (39 mm) and B. cereus (30 mm) at 100 mg/mL[47]. The various extracts of A. catechu heartwood were investigated against Gram-positive bacteria (S. aureus and B. subtilis) and Gram-negative bacteria (S. paratyphi, E. coli, Pseudomonas sp., Enterobacter sp., S. typhi, Shigella sp., Acinetobacter sp., P. mirabilis, and K. pneumoniae). Methanol, diethyl ether, and ethyl acetate extracts are proven to have powerful antibacterial activity among various extracts. Moreover, the MBC of the ethyl acetate extract was 50, 100, 100 and 50 mg/mL against B. subtilis, K. pneumoniae, S. aureus, and Shigella spp, respectively[48].
Phyllodes of the plant Acacia auriculiformis (A. auriculiformis) and Acacia bivenosa were determined for the antibacterial activity against three Gram-positive bacteria (S. aureus, S. pyogenes, and B. cereus) and three Gram-negative bacteria (K. pneumoniae, E. coli, P. aeruginosa). S. aureus, S. pyogenes as well as E. coli responded favorably to the methanol extract of A. auriculiformis phyllodes. At a concentration of 6.0 mg, Acacia bivenosa extract exhibited inhibitions of 0.0-11.0 mm and 0.1-9.7 mm for S. aureus and S. pyogenes as opposed to A. auriculiformis extract, which showed ZOI of 0.2-22.7 mm, 0.1-26.0 mm and 0.2-13.7 mm against S. aureus and S. pyogenes and E. coli, respectively. Additionally, 2.0 mg of Acacia bivenosa extract showed 0.1-8.3 mm inhibition against S. aureus while A. auriculiformis extract showed 0.2-19.0 mm and 0.1-17.7 mm inhibition against S. aureus and S. pyogenes, respectively[49].
Various fractions (n-hexane, dichloromethane, ethyl acetate, and aqueous) of A. catechu bark were analyzed for their antibacterial activity against several bacterial strains including S. aureus ATCC 25923, E. coli ATCC 25922, K. pneumoniae ATCC 13883, S. typhi ATCC 14028, and Shigella sonnei (S. sonnei) ATCC 25931. The results showed that as for the n-hexane fraction, the ZOI was 11 mm and 6 mm against S. aureus and S. sonnei whereas the dichloromethane fraction showed 9 mm and 7 mm of ZOI against S. aureus and S. sonnei. The ethyl acetate and aqueous fractions showed ZOI of 13, 8, and 12, as well as 14, 10, and 10 mm against S. aureus, K. pneumoniae, and S. sonnei respectively. The MIC and MBC against S. aureus ATCC 25923 were tested based on the ZOI and the aqueous fraction of the A. catechu bark extract exhibited MIC and MBC of 6.25 and 12.5 mg/mL, respectively[50].
Olajuyigbe et al. evaluated the antibacterial activity of acetone extract from A. mearnsii stem bark against P. vulgaris KZN, S. aureus OK, E. faecalis KZN, K pneumoniae KZN, P. vulgaris CSIR 0030, B. cereus ATCC 10702, E. coli ATCC 25922, Bacillus pumilus ATCC 14884, S. typhi ATCC 13311, S. marcescens ATCC 9986, K. pneumoniae ATCC 10031, and P. aeruginosa ATCC 19582. The crude extract was most effective against P. vulgaris CSIR 0030 as compared to other tested isolates, with an MIC of 39.1 µg/mL. The MIC values ranged from 39.1 to 625 µg/mL against Gram-negative bacterial strains, whereas those against Gram-positive bacterial strains ranged from 78.1 to 312.5 µg/mL[51].
In a study of Priyanka et al., chloroform, ethanol, ethyl acetate, methanol extracts of leaves and roots of Acacia karoo demonstrated antibacterial effects against various bacterial strains including S. aureus, E. coli, S. typhi, P. aeruginosa, K. pneumoniae, P. vulgaris, and B. subtilis. The methanolic leaf extract showed the maximum inhibition against P. vulgaris with 20.33 mm ZOI and the minimum inhibition against S. typhi with 10.33 mm ZOI. On the other hand, the ethyl acetate extract of Acacia karoo roots showed a maximum zone of inhibition of 33.3 mm against S. aureus while a minimum zone of inhibition of 8.67 mm against E. coli[52]. The summary of the above-mentioned antibacterial activities of Acacia genus is reported in [Table 2].
Table 2: The antibacterial activity of Acacia species using agar diffusion method.2.3. Miscellaneous method-based antibacterial activities of Acacia genus
Different extracts of plant Acacia ataxacantha bark showed varying antibacterial activities against S. aureus ATCC 6538, S. epidermidis CIP8039, E. faecalis ATCC 29212, methicillin-resistant S. aureus, E. coli CIP 53126, and P. aeruginosa CIP 82118. The MIC of different extracts ranged from 325 µg/mL to 5 mg/mL[53]. The flower extract and a fraction of Acacia podalyriifolia were investigated for their antibacterial activities against S. aureus ATCC 6538, S. epidermidis ATCC 12229, and S. pyogenes ATCC 19615, E. coli ATCC 25922, K. pneumoniae ATCC 13883, P. mirabilis ATCC 43071, P. aeruginosa ATCC 27857 and S. typhimurium ATCC 14028. The ethanolic extract and dichloromethane fraction inhibited S. aureus and S. epidermidis with an MIC of 1 mg/mL. Whereas, the ethyl acetate fraction showed MIC values of 0.125 and 0.25 mg/mL against S. epidermidis and S. aureus, respectively, and 0.50 mg/mL against S. pyogenes, K. pneumoniae, and P. mirabilis[54].
Acacia saligna flower water extract was evaluated against four phytopathogenic bacteria, including Agrobacterium tumefaciens, E. cloacae, Erwinia amylovora, and Pectobacterium carotovorum. The MIC values were 200, 300, 300, and 100 µg/mL against Agrobacterium tumefaciens, E. cloacae, Erwinia amylovora, and Pectobacterium carotovorum, respectively[55]. The antibacterial activity of leaf and bark extract and fraction, and isolated compound from Acacia polyacantha leaves was evaluated against E. coli (ATCC8739, ATCC10536, AG102, and AG100Atet), E. aerogenes (ATCC13048, CM64, EA27, and EA289), K. pneumoniae (ATCC11296, KP55, and KP63), Providencia stuartii (ATCC29916 and NEA16), and P. aeruginosa (PA01 and PA124). The MIC value of the leaf crude extract was below 100 µg/mL against P. aeruginosa and Providencia stuartii while for bark extract, the same MIC value was found against E. aerogenes. The results revealed that the extract was moderately effective[56]. A comparative study of fresh and dried leaf extracts of Acacia galpinii, Acacia karroo, Acacia xanthophloea, and Acacia sieberiana (A. sieberiana) was done to evaluate their antibacterial activities against S. aureus ATCC29213 and E. coli ATCC27853. Except for Acacia xanthophloea which was the most active with an MIC value of 78 µg/mL against S. aureus and 160 µg/mL against E. coli, the antibacterial activity of extracts from dried leaves was higher than that of fresh leaves. Moreover, Acacia galpinii extract was the least active (MIC > 5000 µg/mL)[57].
Various extracts of leaf, bark, and root of the plants A. nilotica and A. sieberiana were analyzed for their antimicrobial property against Mycobacterium aurum. The dichloromethane extract of A. nilotica as well as A. sieberiana showed no antimicrobial activity. The MIC value of ethanol extracts of leaves, bark and root of A. nilotica was reported as 0.78 mg/mL, however, the MIC of ethyl acetate extracts of A. sieberiana leaves and roots was 3.12 mg/mL[15]. Palombo et al. tested the antibacterial potential of Acacia kempeana and Acacia tetragonophylla leaf ethanolic extracts against B. cereus ATCC 11778, E. faecalis ATCC 19433, E. coli ATCC 11775, K. pneumoniae ACM number 90, P. aeruginosa ATCC 10145, S. typhimurium ATCC 13311, S. aureus pyogenes ACM 178. According to the results, Acacia kempeana extract showed 9 mm and 6 mm ZOI for B. cereus and E. faecalis, respectively, while Acacia tetragonophylla extract showed 6 mm ZOI for B. cereus[58].
The methanolic leaf extract of Acacia saligna was analyzed for antibacterial activity and was found to be effective against all bacterial strains [Listeria monocytogenes (clinical isolate), E. coli ATCC 35210, S. aureus ATCC 6538, B. cereus ATCC 14579, Micrococcus flavus ATCC 10240 and P. aeruginosa ATCC 27853]. The study revealed that the MIC was (0.31±0.03) and (0.30±0.05) mg/mL against E. coli and S. aureus, respectively, and the MBC was (0.73±0.03), (0.72±0.01), and (0.73±0.03) mg/mL against B. cereus, E. coli, and S. aureus, respectively[59]. The crude water and methanolic extract, as well as isolated compounds of Acacia seyal bark were tested for their antibacterial activity. Except for S. aureus, the water extract exhibited no antibacterial action against all of the bacterial strains. In contrast, the methanolic extract showed antibacterial activity against S. aureus, Corynebacterium urealyticum, and P. aeruginosa[60].
The antibacterial properties of the crude extract and the three main fractions (pet-ether, ethanolic, and methanolic fraction) of Acacia macrostachya stem bark were examined. The high-throughput spot culture growth inhibition assay was used to analyze two Gram-positive bacteria (S. aureus ATCC 25923 and S. pyogenes clinical strain) and two Gram-negative bacteria (E. coli ATCC 25922 and P. aeruginosa ATCC 27853). The MIC against bacterial strains ranged from 250 to 500 µg/mL, with the crude extract having the best results against E. coli with an MIC of 250 µg/mL. Additionally, none of the bacterial strains were inhibited by the pet-ether fraction and none of the extract and fractions were effective against S. aureus[61]. The methanolic and aqueous extracts of Acacia salicina leaves were determined by using the microdilution method against S. aureus ATCC 25923, E. faecalis ATCC 29212, E. coli ATCC 25922, Salmonella enteritidis ATCC 13076 and S. typhimurium NRRLB 4420. The MBC ranged from 0.125 to more than 10 mg/mL, whereas the MIC ranged from 0.0625 to over 10 mg/mL. Hence, the plant leaf extract can be a potent antibacterial drug[62].
Ahmed et al. studied the antibacterial activity of Acacia jacquemontii methanolic and n-hexane extracts against B. subtilis ATCC1692, Micrococcus luteus ATCC 4925, S. epidermidis ATCC 8724, Bacillus pumilus ATCC 13835, S. aureus ATCC 6538, E. coli ATCC 25922, Bordetella bronchiseptica ATCC 7319, and P. aeruginosa ATCC 9027. The highest MIC of the methanolic and n-hexane extract was reported as 0.50 and 1.00 mg/mL against B. subtilis, respectively[63]. The stem bark extract of A. nilotica showed potential antibacterial activity against Streptococcus viridans, S. aureus, E. coli, B. subtilis, and S. sonnei with MIC values of 35 and 50 mg/mL as well as MBC values of 35 and 60 mg/mL against B. subtilis and S. sonnei, respectively[64]. The antibacterial activity of A. sieberiana stem bark, root bark, and leaves was examined against many bacterial strains, including S. paratyphi ATCC 9150, K. pneumoniae ATCC 13883, S. sonnei ATCC 25931, E. cloacae ATCC 23355, P. aeruginosa ATCC 27853, E. coli ATCC 25922, and E. faecalis ATCC 25923. All of the test bacteria were susceptible to the crude plant extracts. Root bark and stem bark showed significant antibacterial activity with MIC values of 0.16 mg/mL to 2.5 mg/mL[65]. Furthermore, Muddathir et al. determined the antibacterial activity of methanolic extract and its 4 elucidated fractions [F1-4] from A. nilotica bark against Streptococcus sobrinus and Porphyromonas gingivalis by using broth dilution method. The crude extract of A. nilotica showed MIC and MBC values of 0.5 mg/mL and 2 mg/mL against Streptococcus sobrinus and Porphyromonas gingivalis, respectively. However, the fractions (F1 and F2) showed an MIC value of 0.3 mg/mL against Porphyromonas gingivalis. F2 also displayed an MBC value of 1 mg/mL against both bacteria[66]. The summary of the above-mentioned antibacterial activities of Acacia genus is reported in [Table 3].
Table 3: The antibacterial activity of Acacia species using miscellaneous method. 3. Antifungal activities reported in Acacia genus Fungal infections are the main cause of sickness and mortality in people with immunological deficiencies, and they can be fatal in both developed and developing countries[67],[68]. The majority of fungal infections are persistent and frequently require extended chemotherapy and involve specific dangers for persons with impaired immune systems[69]. The various antifungal activities reported in Acacia genus are highlighted in this section.
3.1. Disc diffusion method-based antifungal activities reported in Acacia genus
Two different Acacia species A. arabica and Acacia raddiana (A. raddiana) were studied for the antifungal activity against Candida albicans (C. albicans) and Aspergillus niger (A. niger). The ZOI diameter of A. arabica and A. raddiana extracts was 36.10 and 37.50 mm against C. albicans, as well as 59.50 and 68.40 mm against A. niger, respectively. Additionally, the MIC values for A. arabica extract were found to be 0.105 and 0.079 mg/mL against C. albicans and A. niger, respectively, whereas for A. raddiana extract, 0.088 and 0.079 mg/mL against C. albicans and A. niger, respectively. On the other hand, the minimum fungicidal concentration (MFC) for A. arabica was 0.105 and 0.158 mg/mL, while for A. raddiana, 0.088 and 0.158 mg/mL against C. albicans and A. niger, respectively[70].
The aqueous extract of A. nilotica leaves was screened against fungal strains [C. albicans, A. niger, and Aspergillus fumigatus (A. fumigatus)] to verify its antifungal activity. The ZOI was 10 and 11 mm against C. albicans at 10 and 20 mg/mL, respectively, 8, 8, and 12 mm against A. niger at 5, 10, and 20 mg/mL, respectively, and 8, 9, and 13 mm against A. fumigatus at 5, 10, and 20 mg/mL, respectively. However, no inhibition was observed at 2.5 mg/mL against each strain[71]. The isolated compounds from Acacia ataxacantha were analyzed for antifungal activity against C. albicans. The isolated compounds i.e., lupeol and betulinic acid did not show any activity against the test organism at 100 µg/mL whereas betulinic acid-3-trans-caffeate was effective against the test organism with a ZOI of 15.7 mm at the same concentration. The MIC and MFC of betulinic acid-3-trans-caffeate were 12.5 and 25 µg/mL, respectively[40]. The summary of the above-mentioned antifungal activities of Acacia genus is reported in [Table 4].
Table 4: The antifungal activity of Acacia species using disc diffusion method.3.2. Agar diffusion method-based antifungal activities of Acacia genus
A comparison of two different Acacia species Acacia mangium and A. auriculiformis was performed based on their antifungal properties. The heartwood extract, fraction, and isolated compounds of the plants were tested against two fungal strains Phellinus noxius and Phellinus badius using agar dilution bioassay. The results revealed that the methanol extract was found to be most effective against fungal growth. As compared to A. auriculiformis, Acacia mangium extracts had little or no effect on the growth of Phellinus badius and Phellinus noxius[72]. Five different extracts (n-hexane, chloroform, diethyl ether, ethyl acetate, and methanol) of A. catechu heartwood were determined for the antifungal properties against Fusarium moniliforme (F. moniliforme), Fusarium oxysporum (F. oxysporum), Exherlium turticum (E. turticum) and Fusarium proliferatum. The ethyl acetate extract displayed the highest ZOI against F. oxysporum. In comparison, the n-hexane extract demonstrated weak activity with a ZOI of 8 mm against F. moniliforme whereas the chloroform and methanol extracts displayed moderate activity with ZOI of 9, 9, and 10 mm, against F. oxysporum, F. moniliforme and E. turticum, respectively and 10, 7, and 8 mm against F. oxysporum, Fusarium proliferatum and E. turticum, respectively. Moreover, the diethyl ether and ethyl acetate displayed good activity with ZOI of 10, 11, 10, and 11 mm and 17, 9, 9, and 14 mm against F. oxysporum, F. moniliforme, Fusarium proliferatum, and E. turticum, respectively[48].
According to the study of Bwai et al., the fruit extracts of A. nilotica exhibited antifungal efficacy at doses from 125 mg/mL to 500 mg/mL. The extracts displayed ZOI of 9.00 mm to 17.00 mm against A. niger and Aspergillus flavus (A. flavus), respectively, whereas F. oxysporum was inhibited by the extracts at 500 mg/mL and 250 mg/mL with ZOI of 11.00 mm and 9.00 mm, respectively. However, only at 500 mg/mL, A. nilotica extracts exhibited antifungal activity against Penicillium spp[73]. The antifungal activity of A. tortilis gum aqueous extract was analyzed against eight fungal strains including Aspergillus ochraceus, A. fumigatus, A. niger, Aspergillus parasiticus, Penicillium expansum, A. flavus, F. oxysporum, and Alternaria sp. The aqueous extracts demonstrated enhanced antifungal activity with increasing extract dilution (1/100, 1/250, 1/500, 1/1000 and 1/5000). Among all fungal strains, F. oxysporum showed more resistance to the extracts[74].
The heartwood ethanolic extract and three fractions (petroleum ether, benzene, and ethyl acetate) of A. raddiana were found to be effective as an antifungal agent. The results showed that the ZOI of the ethanolic extract against C. albicans was 9.60 mm and the petroleum ether fraction effectively prevented all fungal strains. However, with 10.42 mm ZOI, C. albicans and Trichophyton rubrum showed the maximum inhibition. In addition, the benzene fraction was effective against all the fungal strain with the maximum inhibition of 10.21 mm against Trichophyton rubrum and C. albicans, respectively[75]. The crude extracts of Acacia ampliceps stem bark were determined for their antifungal activity against four fungal strains Acremoniums spp, A. niger, Rhizopus spp, and Trichoderma. The results showed that A. niger was more susceptible to the extracts than Rhizopus and Acremonium spp. The methanolic extract was more potent as compared to the ethanolic extract with the ZOI of 20, 20, and 22 mm at 1000 µg/mL against Acremonium spp, Rhizopus spp., and Trichoderma, respectively[76].
Nilobamate isolated from A. nilotica was evaluated for antifungal activity against two fungal strains (A. fumigatus and C. albicans). Mbatchou et al, pointed out that the compound showed varying degrees of inhibition against A. fumigatus at different concentrations with no inhibitory activity against C. albicans[77]. A. catechu bark ethanolic extract was analyzed based on its antifungal activity against three human pathogenic fungal strains (Microsporum gypseum, Epidermophyton floccosum, and Trichophyton rubrum). It was noted that the ethanolic extract had no significant effect on each strain and could not be further used for cutaneous infection[78]. The methanolic and aqueous extracts of Acacia concinna leaf and seed were analyzed for its antifungal activity against some fungal strains [Alternaria alternata (A. alternata) K3, F. oxysporum S10, Fusarium solani L16, A. flavus J12, and Colletotrichum falcatum Went C9]. The results showed that the Acacia concinna extracts inhibited fungal growth[79]. The summary of the above-mentioned antifungal activities of Acacia genus is reported in [Table 5].
Table 5: The antifungal activity of Acacia species using agar diffusion method.3.3. Miscellaneous method-based antifungal activities of Acacia genus
The ethanol extracts of Acacia robusta leaf and A. nilotica stem bark were screened for antifungal properties against [C. albicans, Candida glabrata, Candida parapsilosis, Candida tropicalis, Candida krusei (C. krusei), and Cryptococcus neoformans]. The MIC values of Acacia robusta were 1000, 63, 500, 31, and 4000 µg/mL against Candida glabrata, Candida parapsilosis, Candida tropicalis, C. krusei, and Cryptococcus neoformans, respectively, while for A. nilotica, 31, 63, 1000, and 4000 µg/mL against Candida parapsilosis, Candida tropicalis, C. krusei, and Cryptococcus neoformans, respectively[80].
The in vitro antifungal potential of A. senegal and A. tortilis was assessed against Helminthosporium rostratum, Fusarium solani, and A. alternata. At concentrations of 1.0%, 2.5%, and 5.0%, the aqueous extracts of A. senegal showed no inhibition against A. alternata. Moreover, A. senegal aqueous extracts exhibited a slight effect on the growth of Helminthosporium rostratum at 2.5% and 5.0% concentrations but no antifungal activity at 1.0% concentration. The growth of A. alternata was unaffected by the aqueous extract of A. tortilis at concentrations of 1.0% and 2.5%. However, at 5.0% concentration, it inhibited the growth of A. alternata by 47.9%. Furthermore, Helminthosporium rostratum showed no activity at 1.0% concentration, but at 2.5 % and 5.0%, it showed 5.3% and 43.8% of inhibition, respectively. Whereas, the modest efficacy of the extract of A. tortilis against Fusarium solani increased with increasing concentrations, showing 8.8%, 18.5%, and 19.4% of inhibition, respectively[81].
The leaf and stem methanolic extracts of Acacia karoo were determined for the antifungal property against C. albicans and Microsporum audouinii. The MIC value was 78.12 and 625 µg/mL for the leaf extract while 156.25 and 78.12 µg/mL for the stem extract against C. albicans and Microsporum audouinii, respectively. Additionally, the MFC value was 312.50 and 1250 µg/mL for the leaf extract, whereas 312.50 and 312.50 µg/mL for the stem extract against C. albicans and Microsporum audouinii, respectively[3]. Acacia mangium bark extract (acetone, toluene, and water) was examined to verify its antifungal property by using two fungal strains (Coriolus versicolor and Poria placenta). The ZOI of the acetone, toluene/ethanol, and water extracts was reported as 2.55, 2.00, and 5.29 mm and 6.86, 2.35, and 15.10 mm against Coriolus versicolor at 100 and 500 ppm. In contrast, the ZOI of acetone, toluene/ethanol, and water extracts was 5.69, 4.71, and 52.35 mm and 23.92, 42.16, and 55.59 mm against Poria placenta at 100 and 500 ppm[82].
The crude acetone extract of A. mearnsii stem bark was evaluated against 12 fungal strains (C. albicans, Candida rugosa, C. krusei, Aspergillus terreus, A. flavus, Trichophyton tonsurans, Penicillium notatum, Absidia corymbifera, A. niger, Fusarium sporotrichioides, Trichophyton mucoides ATCC 201382, and Candida glabrata ATCC 2001). The MIC and MFC ranged between 625-5000 µg/mL and 625-5000 µg/mL against various fungal strains, respectively[51]. The summary of the above-mentioned antifungal activities of Acacia genus is presented in [Table 6].
Table 6: The antifungal activity of Acacia species using miscellaneous method. 4. Conclusion The antimicrobial activities including antibacterial and antifungal activities of Acacia are highlighted in this article. The various bacterial and fungal stains such as S. aureus, E. coli, S. typhi, P. aeruginosa, K. pneumoniae, and C. albicans, F. oxysporum, A. niger, and A. flavus are inhibited by various extracts and phytoconstituents of Acacia. Overall, Acacia genus possesses moderate to high microbiological activity. Most of the species of Acacia genus are well explored for in vitro antimicrobial activities, but proper molecular mechanisms are still an issue of concern. Therefore, Acacia genus can be further explored for molecular pharmacological studies to produce potent antimicrobial agents.
Conflict of interest statement
All authors declare no conflict of interest.
Acknowledgments
All authors are thankful to the ISF College of Pharmacy, Moga, Punjab for providing the essential facilities required in the compilation of this manuscript.
Funding
The authors received no extramural funding for the study.
Authors’ contributions
NKR contributed to conceptualization; DA was responsible for design of study and supervision, literature search, writing, and original draft preparation. Both NKR and DA contributed to the final version of the manuscript. All authors have read and agreed to the published version of the manuscript.
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