Abstract

Background: Gastroenteritis is caused by infection and/or inflammation of the digestive tract. The symptoms of this illness include diarrhea and/or stomach cramps and may include fever, headache, blood in feces, loss of appetite, bloating, and body aches. Gastroenteritis is mainly caused    by    bacteria    including    Campylobacter,    some     strains     of Escherichia    coli, Salmonella, Shigella, and Staphylococcus aureus.

Despite the availability of individual treatment, antibiotic resistance is becoming a worldwide problem posing danger to humanity as various diseases and infections that are formerly treated with this substance are now difficult to control. The emergence of antibiotic resistance as well as the recent undesirable side effect of some of the commercially available antibiotics has led to the screening of plant extracts in search for new drug that could serve as alternative therapy for the treatment of various infections and diseases.

However, this study was aimed to investigate the antibacterial activity of the aqueous leaf extract of scent leaf(ocimum gratissimum) on Escherichia coli. Methods:This study employed an experimental design where E.coli bacteria was cultured and the isolates were collected and invitro testing was done to investigate the antibacterial activity of the aqueous leaf extract of scent leaf(ocimum gratissimum) at different concentrations that is 200mg/mL, 100mg/mL, 50mg/mL and 25mg/mL on E.coli.

Results: Results shows that Ocimum gratissimum leaf extract at 200mg/mL had an inhibition zone of 10mm and as concentration dropped to 100mg/mL,its effect on E.coli decreases with an inhibition zone of 8mm, and as concentration dropped to 50mg/mL and 25mg/mL, it has no effect on E.coli with no inhibition zone implying that this extract at lower concentrations produces no significant effect on E.coli.

The minimum inhibitory concentration was determined to be between 100mg/mL and 50mg/mL of the extract on E.coli. The results obtained from this study showed that the leaf extract of the plant inhibited the growth of the test isolates at varying concentrations and 100mg/mL been determined as the MIC.Since Gram-negative bacteria such as E.coli were sensitive to the the inhibitory effect of this extract,the presence of this phytochemicals such as saponnins, tannins and flavonoids in Ocimum gratissimum accounts for its usefulness as medicinal plants. Conclusion: Ocimum gratissimum leaf extract showed an activity against E.coli in-vitro and its can be beneficial as a source of therapeutic agents which may pave a way in the ongoing search for antibacterial agents from plant sources.

CHAPTER ONE

INTRODUCTION

1.1 Background of the Study

Pathogenic gastrointestinal bacteria are bacteria that cause gastroenteritis (Okigbo and Igwe, 2007). They infect the gut leading to inflammation of the stomach and intestines (Ishiwu et al., 2014). This leads to vomiting, severe abdominal cramps, and diarrhea. They include Escherichia coli, Shigella species, and Salmonella species. Bacterial gastroenteritis commonly occurs as a result of poor hygienic practices (Russell and Jarvis, 2011). However, infections can also occur after close contact with infected animals or consuming food or water contaminated with bacteria or the toxic substances produced by bacteria (Opara et al.,  2014).

1. coli are commonly found in fecaloid matters and can cause serious food poisoning in their hosts (Kotloff et al., 2013). Shigella spp. causes shigellosis, commonly referred to as bacterial dysentery (Ram et al., 2008). Salmonella spp. are facultative intracellular pathogens. They are two serotypes; the non-typhoidal and typhoidal serotypes. The non-typhoidal serotype invades only the gastrointestinal tract and cause Salmonella food poisoning while the typhoidal serotype spreads throughout the body, invades organs, and secretes endotoxins (Su and Chiu, 2007). Currently, diarrhea is the second leading cause of death in children aged less than 5 years and is responsible for approximately 760,000 children deaths every year, Children who are malnourished or have impaired immunity and people living with HIV are at considerable risk of life-threatening diarrhea ( Bebell et al.,2014).

Antibacterial are forms of antimicrobial agent used especially against bacteria, for the treatment of bacterial infections (Prabhu et al., 2009). The discovery of antibiotics (a substance produced by microbes which inhibit or kill another microorganism at a very low concentration) has helped in the control of pathogenic bacteria until the recent development of resistance by most pathogens. Antibiotic resistance is becoming a worldwide problem posing danger to humanity as various diseases and infections that are formerly treated with this substance are now difficult to control (Suree and Pana, 2015). In addition, some synthetic available antibacterial agents are becoming ineffective due to their side effects such as tendonitis, seizure, and Steven-Johnson syndrome (WHO, 2002).

The emergence of antibiotic resistance as well as the recent undesirable side effect of some of the commercially available antibiotics has led to the screening of plant extracts in search for new drug that could serve as alternative therapy for the treatment of various infections and diseases (Effraim et al., 2013). The rise of infections caused by multidrug-resistant (MDR) bacteria has become a worrying public health problem (Vivas et al.,2019). The occurrence of these strains is frequently related to strong selective pressure caused by indiscriminate and inadequate use of antibiotics in hospitals (Karam et al.,2016). However, this is not a problem restricted to a nosocomial environment, as it can also be related to infections caused by foodborne pathogens (Chan et al.,2018). In addition, another important issue is the ability of several bacteria to form a complex multicellular structure, called biofilms (Davies et al.,2017)

These tridimensional communities are built mainly by bacterial cells embedded into extracellular polysaccharides secreted by themselves (Makovcova et al.,2017) and this arrangement reduces the effectiveness of antimicrobial agents (Thurlow et al.,2011) Thus, antibiotic resistance reduces the number of therapeutic options and causes an increase in hospitalization costs/time of patients, thus increasing the morbidity/mortality rates (Van Duin et al.,2016). Moreover, the unwanted side effects  (toxic, teratogenic and/or mutagenic, reaction of hypersensitivity, and so on), high cost, and environmental problems of antibiotic drugs are of serious concern (Ojeda-Sana et al.,2013). As such, novel antibacterial agents, especially plant-derived natural products, must be developed.

Ocimum gratissimum popularly referred to as Scent leaf belongs to kingdom plantae, order lamiales, family lamiaceae, genus Ocimum, species Ocimum gratissimum and binomial name Ocimum gratissimum. It is a tropical shrub that grows to between 50cm to 80cm tall in height. The leaves are oval in shape, serrated at margins and opposite in arrangement. The flowers are often white in colour (Obvute, 2006). Ocimum gratissimum referred to as scent leaf because of its aroma is commonly used as spices for food or soup preparation in Nigeria. It is a medicinal plant which has been used traditionally for the treatment of various infections (Abdullahi, 2005).

The plant is cultivated in abundant in different part of Nigeria and it contains some bioactive substances such as tannins, saponins, alkaloids, glycosides, phenols and flavonoids, also referred to as phytochemicals. These phytochemicals when consumed served as medicine for protection and treatment of human or animal disease (Abdullahi, 2005) The in-vitro antimicrobial screening of O. gratissimum against Staphylococcus aureaus, E. coli, Streptococcus fecalis, Psudomonas aeruginosa and Lactobacilli showed that the leaf extract is effective against human pathogens (Prabhu et al., 2009).

According to World Health Organization medicinal plants would be the best source to obtain a variety of drugs. In developed countries about 80% of plants are used in traditional medicine. Therefore, such plants have been investigated for the betterment of understanding of their medicinal properties. The antimicrobial properties of many plants have been investigated by  number of researcher’s worldwide (Adamu et al., 2005).

Plants have been a source of medicine in pharmacopoeia (British, United States or any other). Herbal medicine can be served as an alternative treatment for some commercial drugs (Anyamene and Ezeadila, 2010). Medicinal plants provide inestimable projections for new drug discoveries because of the matchless availability of chemical range. The practice of herbal medicines in Asia signifies a long antiquity of human interactions with the environment (Sasidharan et al., 2011).

In Thailand, this plant has  been  consumed freshly  or used  as  food spice. Essential  oil  of fresh  leaves of Ocimum gratissimum (OGEO) exhibits various biological activities, including antibacterial (Zhang et al.,2017), antifungal (Ruhal et al.,2015), antioxidant (Chauhan et al.,2014), anticandidal (Ghosh et al.,2013), and antinociceptive (Koh et al.,2013). In addition, OGEO is used as food preservative against mycotoxigenic fungi and as a wound-healing promoter (Essid et al.,2017). As candidate bio-agents, essential oils have long been documented to be effective antimicrobial compounds against various pathogens (Ksouri et   al.,2017).

Rosemary   oil   displayed    antibacterial    activity    against S. aureus, Enterococcus faecalis, E. coli and Klebsiella pneumoniae with a MIC in the range  of 10–40 μl ml−1 (S. Burt.,2004) Sienkiewicz et al studied the susceptibility of various pathogenic wound bacteria (S. aureus, E. faecalis, E. coli, K. pneumoniae, Enterobacter cloacae and Actinobacter baumannii) against several essential oils and found that clove oil and thyme oil displayed the highest activity with a MIC about 0.5–1.5 μl ml−1, followed by cinnamon oil (MIC 1.0–1.25 μlml−1).

Germanium, lavender, clary sage and basil showed moderate antibacterial activity with a MIC in the range of 2.75–9 μl ml−1, rosemary oil showed the weakest antibacterial effect (MIC 13–19 μl ml−1). Thymol, cinnamaldehyde and  eugenol are considered to be the active and major component in thyme oil, cinnamon oil and clove oil, respectively.  Essential  oils   from Origanum   floribundum,   rosemary   and Thymus   ciliatus displayed anticandidal effect with MIC in the range of 15–30 μg ml−1 (Oussalah et al.,2006).

Rosemary oil has lowest anticandidal property which may be related to the major composition of the  oil.  Thymol  is  the  major  composition  of  the  oil  from O.  floribundum and Thymus ciliates, whereas rosemary oil contains high percentage of α-pinene and 1,8-cineole. Cinnamon (Cinnamomum verum) and clove oil also displayed potent anticandidal activity with MICs in the range of 31.25–62.5 μg ml−1 and 125–250 μg ml−1, respectively (Kpadonou Kpoviessi et al.,2014). Hence, essential oils are a viable alternative to classical antibiotics. In remote areas, particularly developing countries, the access to modern antibiotic agents may be impractical. Consequently, essential oils and/or plant-bearing essential oils are used to fight against microbial pathogens.

1.2. Statement of problem

Antibiotic resistance is becoming a worldwide problem posing danger to humanity as various diseases and infections that are formerly treated with this substance are now difficult to control (Suree and Pana, 2015). In addition, some synthetic available antibacterial agents are becoming ineffective due to inadequate, irrational use of these antibiotics which leads to their side effects such as tendonitis, seizure, and Steven-Johnson syndrome (WHO, 2002).

However, the increasing problems of multi-drug resistant (MDR) bacteria is of great concern to both the clinicians and pharmaceutical industries and therefore there is a need for the formulation of new antibacterial agents from plant extracts that are highly effective, affordable, acceptable and available to overcome this resistance and improve treatment outcomes. (Martino et al., 2002; Akinjogunla et al.. 2010). This study therefore has been designed to investigate the antibacterial activity of the aqueous plant extract of Ocimum gratissimum on Escherichia coli. If this experiment shows promising effect, further studies would be carried out concerning this drug development and precision in the dose regimen determined and even prescription practices to treat bacterial infection will be employed.

1.3 Research Questions

1. What is the antibacterial activity of the aqueous extracts of Ocimum gratissimum on the growth of Escherichia coli?
2. What is the minimum inhibitory concentration of the aqueous extract that is required to inhibit or stop the growth of Escherichia coli?
3. What are the phytochemicals responsible for the antibacterial activity of Ocimum gratissimum against Escherichia coli?

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