Antimicrobial and antioxidant activities of Tea plant

Many complementary and alternative medicines have enjoyed increased popularity in recent decades. Efforts to validate their use have seen their putative therapeutic properties, which come under increasing scrutiny in vitro and in some cases in vivo . One of such products is tea and its tree oil (TTO); which is a secondary metabolite derived from tea plant ( Melaleuca alternifolia ). Both black and green tea has several polyphenolic compounds with possible antibacterial effects. It is employed largely due to its antimicrobial properties, and is incorporated as the active ingredient in many topical formulations used to treat cutaneous infections, in addition to being marketed as a remedy for various ailments. The essential oil of M. alternifolia exhibits broad-spectrum antimicrobial potential. The TTO may help to treat severe yeast infections. Results also suggested that TTO exerts a greater bactericidal potency against bioﬁlm-grown methicillin-resistant Staphylococcus aureus (MRSA), and methicillin-sensitive Staph. aureus (MSSA) strains. Moreover, tea has inhibitory efficacy against the carcinogenic bacteria.


Introduction
Plant materials are widely used in developed and developing countries as home remedies, over the counter drug products and raw materials of the pharmaceutical industry. They represent a substantial proportion of the global drug market (Kunle et al., 2012). Many complementary and alternative medicines have increased their popularity in recent decades (Kyungseop, 2017). According to previous studies of Martins, (2013); Napatt et al., (2019), tea (Camellia sinensis) is the second most consumed beverage in the world next to water. In a recent study, Reygaert, (2017) reported that tea belongs to the family Theaceae, and is a product made by processing the leaves or buds. All tea varieties such as, green, oolong and black tea, are harvested from this species. Tea extracts work as effective treatments for patients who suffer from damaged skin following radiation treatment for cancer. Several previous studies of Priyanka et al., (2012); Ohishi et al., (2016); Arina et al., (2017) revealed that this might partly be due to the antiinflammatory properties of tea. Moreover, Arina et al., (2017) added that tea acts at the cellular level by inhibiting the inflammatory pathways, and lowering the release of pro-inflammatory cytokines including; IL-1beta, IL-6, IL-8, TNF alpha, PGE2, and white blood cells in human cell lines. Green tea extract had been shown to be potent in neuro-protectant (Orly et al., 2009). A study conducted by Qin et al., (2012) suggested that the intracellular amyloid beta (iAβ)induced toxicity was significantly inhibited by green tea polyphenols in cultured rat primary cortical neurons. Previous studies of Li et al., (2007);Qin et al., (2012) reported that the intracellular iAβ toxicity is related to the development of Alzheimer's disease. In another study of Cong et al., (2016), it was explored that green tea polyphenols inhibit glutamate-induced neurotoxicity which is linked to neurodegenerative diseases.

The effects and mechanism of action of tea
Tea contains several naturally occurring dietary polyphenols such as catechins, which possess anticarcinogenic activity that act as effective chemopreventive agents against the initiation, promotion and progression stages of multistage carcinogenesis. Usually, all the four types of tea could lower the total cholesterol levels (Aleksandra et al., 2016). Black tea has only about one-sixth of the antioxidant power of green tea, owing mainly to the former's low levels of catechins (Anton and Sheila, 2003). On the other hand, Duh et al., (2004) reported that although the polyphenolic compositions of all the four types of tea were dramatically different, they have nearly identical levels of antioxidant potential. Agnieszka and Wilfried, (2014) suggested that the strong antioxidant catechins in green tea are destroyed by the fermentation reactions, leading to oolong, black and Puer teas. Previously Jie et al., (2006) revealed that there is a compensatory gain in the antioxidant activity of tea due to the new compounds produced.
Several years before, Chen et al., (2005) discovered that extracts of Puer and black teas were effective inhibitors of the virus protein-destroying enzyme (called 3CLPro), responsible for Severe Acute Respiratory Syndrome (SARS). In addition, they identified three compounds found in fully fermented teas mainly; tannic acid, theaflavin-3'gallate and theaflavin-3,3'-digallate, acting as effective 3CLPro inhibitors. In another study, Kuo et al., (2005) reported that Puer and oolong significantly lowered the triglyceride levels, whereas green and black did not. Previously, Zhao et al., (2002);Blanco et al., (2005) reported that the properties of green tea inhibit the bacterial growth, which are mainly related to their polyphenolic components including; epicatechin, epicatechin gallate, epigallocatechin, and epigallocatechin gallate, against various Gram-positive and Gramnegative bacteria. Moreover, Zhao et al., (2002);Hu et al., (2002);Stapleton et al., (2004);Cho et al., (2008) added that green tea have a synergistic effect with β-lactam antibiotics against Methicillinresistant Staphylococcus aureus (MRSA). In a previous study, Zhao et al., (2001) revealed that the main components of tea as polyphenols, epigallocatechin gallate, can reverse the methicillin resistance of MRSA by inhibiting the synthesis of Penicillin-binding Protein-2 (PBP2), and may also prevent adhesion to the mammalian epithelial cells (HEp-2) without any probable alteration (Janecki and Kolodziej, 2010;Sharma et al., 2012). It has been proposed by Lee et al., (2009) that green tea leaves extract can prevent the attachment of pathogenic bacteria on the host cell membrane, which in turn acts as a potential anti-adhesive agent. Chung et al., (2003) previously documented that green tea extract may affect the activity of dihydrofolate reductase, an enzyme that is needed by the pathogenic bacteria to synthesize purine and pyrimidine, as well as to increase the thickness of the epidermis.

The tea tree oil (TTO)
Novel Research in Microbiology Journal, 2019 Recently, TTO has gained a good reputation as a safe, natural and effective antiseptic, and is employed significantly due to its antimicrobial properties. During the study of Carson et al., (2006), it was reported that TTO is incorporated as the active ingredient in many topical formulations used to treat cutaneous infections. The chemical composition of TTO has been well defined, and it consists largely of cyclic monoterpenes of which about 50% are oxygenated, whereas the other 50% are hydrocarbons (Cox et al., 2000;Carson et al., 2006). TTO exhibits a broad-spectrum of antimicrobial activity which can be primarily attributed to the presence of terpinen-4-ol. Previously, Cox et al., (2000) observed that the essential oil of M. alternifolia exhibited broadspectrum antimicrobial activity, while TTO caused leakage of K ion in Escherichia coli, Staphylococcus aureus and Candida albicans. Moreover, it has the ability to disrupt the permeability barrier of the cell membrane structures leading to the loss of chemiosmotic control, which is the most likely cause of its lethal action at minimum inhibitory levels. Hammer et al., (2000) stated that germ tube formation (GTF) by C. albicans is affected by the presence of and\ or the pre-exposure to subinhibitory concentrations of TTO. In addition, TTO has been suggested by Hammer et al., (2000); (2003) as a potential agent for MRSA decolonization.
In a previous study, Hammer et al., (1996) suggested that TTO could be useful for removing the transient skin flora, while suppressing but still maintaining the resident flora that acts as a natural defense against colonization by other pathogenic bacteria. In spite of having similar minimum inhibitory concentrations (MIC)/ minimum bactericidal concentrations (MBC) values, the microorganisms studied by Cox et al., (2000) expressed obvious differences in their susceptibility to TTO. Previous work of Messager et al., (2005) showed that the hand-cleansing formulations contain 5% TTO and 10% alcohol, or a solution of 5% TTO in water, which are more effective than soft soap in removing bacteria from the surface of the hand. Aaron et al., (2006) studied the in vitro antibacterial activity of TTO against clinical skin isolates of methicillin-resistant S. aureus (MRSA), methicillin sensitive S. aureus (MSSA), and coagulase-negative Staphylococci (CoNS) growing as biofilms, and concluded that TTO exerted a greater bactericidal potential against the biofilm-growing MRSA and MSSA isolates, than against some of the biofilmgrowing CoNS isolates. -Marshall et al., (2001) reported that TTO is bactericidal in nature, although it may be bacteriostatic at lower concentrations. The activity of TTO against antibiotic-resistant bacteria has attracted considerable interest, especially with methicillin-resistant S. aureus (MRSA) receiving the most attention so far. In a previous study, Inouye et al., (2001) reported that vaporized TTO can inhibit several bacteria spp. including; Mycobacterium avium ATCC 4676, E. coli, Haemophilus influenzae, Streptococcus pyogenes, and S. pneumoniae. Treatment of S. aureus with TTO resulted in the leakage of K ions (Cox et al., 2000;Hada et al., 2003), and inhibited its respiration (Cox et al., 2000). Reichling et al., (2002) stated that treatment with TTO sensitized S. aureus cells to sodium chloride, and caused morphological changes. Similarly, Noormandi and Dabaghzadeh, (2015) reported that the polyphenolic components of green tea have antibacterial potential.

The antifungal potential of TTO
Several years before, Senthaamarai et al., (2015) pointed that the germinated fungal conidia are significantly more susceptible to TTO than nongerminated ones, suggesting that the intact conidial wall confers considerable protection. In addition, TTO vapors have also been reported to inhibit fungal growth and affect their sporulation (Schnitzler et al., 2001), and they also inhibit the formation of germ tubes or mycelial conversion in C. albicans (Schnitzler et al., 2001). Noumi et al., (2011) reported that at low concentrations as 0.3125 mg/ ml of tea tree essential oil and 0.078mg/ ml of eucalyptus oil, they drastically impair the maximum yield and growth rate of C. albicans and C. glabrata, suggesting that essential oils can be used as part of the efficient oral hygiene regime.

The antiviral efficacy of TTO
Previously, Schnitzler et al., (2001) documented that at high concentration of TTO (0.003%), it reduced Herpes Simplex Virus (HSV-1) titers by 98.2%, and HSV-2 titers by 93.0%. They also reported that by applying TTO at different stages of the virus replicative cycle, it had the greatest effect on the intact virus (prior to infection of cells); however, when it was applied during the adsorption period, a slight reduction in the plaque formation was observed. Another study by Mikus et al., (2000) evaluated the activities of 12 different essential oils including TTO for their activities against HSV-1 in Vero cells, where TTO exerted most of its antiviral activity on the free virus. They observed that 1% of the essential oils inhibited plaque formation completely, while 0.1% TTO reduced plaque formation by approximately 10%.

Antioxidant and antimicrobial activities of Tea
Compared with other types of tea, green tea is undoubtedly one of the most potent natural preservatives applied to many foods as antioxidant and antimicrobial agents (Zhu et al., 2005;Almajano et al., 2008;Su et al., 2008;Kristanti and Punbusayakul, 2009). Several previous studies of Sakanaka et al., (2000); Wang et al., (2000) have demonstrated the antimicrobial efficacy of green tea extract in vitro against some potent pathogens such as; Shigella dysenteriae, Salmonella sp., E. coli, S. aureus and Listeria monocytogenes.
The antioxidant activity of green tea extract has also been verified in raw, frozen and cooked meat patties (Jo et al., 2003;Mitsumoto et al., 2005), and in sausage (Bozkurt, 2006). Previously, Kristanti et al., (2014) investigated the effects of two brands of commercial Assam green tea infusion on the microbial growth, anti-lipid oxidation and color change in cooked beef, and recorded a significant reduction in the populations of Staph. aureus, Listeria monocytogenes, S. typhimurium and E. coli, to an undetectable level in the cooked beef within 2 d of storage at 4 o C. In previous studies, Pokorný et al., (2001);Michalczyk and Zawislak, (2008) pointed that besides acting as antimicrobial agents, the polyphenolic compounds in green tea are primarily known as antioxidant agents that can retard the free radical chain reaction during the process of oxidation. Dorota, (2014) studied the effect of addition of green tea on the selected properties of probiotic milk, and reported that green tea can be successfully employed as a functional supplement for probiotic milk, as it added an extra value to the known health benefits of the probiotics. Moreover, Maksum et al., (2013) concluded from their study that C. sinensis leaves extract could be useful in combating emerging drug-resistance caused by MRSA and P. aeruginosa.

Conclusion
Different tea products have different biochemical profiles, and are great sources of antioxidants. Tea has inhibitory activities on carcinogenic and periodontopathic bacteria. Therefore, it can be inferred that the combined use of tea and antibiotics could be useful in fighting the emerging drug resistance problem. However, there are many improvements and experiments that need to be carried out in the future to determine the effectiveness of tea products.