Antibiotics to a large extent have helped protect people from infections and have become widely available; this unique class of drugs is losing its effectiveness from overuse. The more exposure bacteria have to an antibiotic, the more likely they will develop resistance to the antibiotic. Increasing resistance of microorganisms to antibiotics and other orthodox drugs has resulted in the search for more organic molecules from plant source with antimicrobial properties. Therefore African medicinal plants’ study and investigation is of great significance. Phytochemical composition of plants are abundant with tannins, saponins, alkaloids, flavonoids, cardiac glycosides and phytosterols (Nair et al, 2007), which serve as bioactive precursors have shown to exhibit antimicrobial characteristics. In ethnopharmacology research, the antimicrobial susceptibility test (AST) is used to determine the efficacy of potential antimicrobial species. AST methods are used to screen plant extracts for antimicrobial activity but are largely used to determine the usefulness of an antimicrobial in combating infections by determining its minimum inhibitory concentration. In clinical research in vitro susceptibility tests are particularly important if an organism is suspected to belong to a species that has shown resistance to frequently used antimicrobial agents of which the study organisms are part of them. (Kamba et al., 2010). The array of secondary metabolites produced by plants is daunting, with wide ranging chemicals, physical and biological activities. These constitute a source of bioactive substances which are hypothetically the reason for the perceived recognition being antimicrobial. Antimicrobial extracts serve as plant defense mechanism against predation by microorganisms, insects and herbivores. Some such as terpenoids give plants their odors, others (quinones and tannins) are responsible for plant’s pigments (Cowan, 1999). Therefore, analogously, these metabolites and extracts are meant to be used initially to prevent microbial infestation of the plants (a defense mechanism) but these extracts are not discriminatory, that is to say that when prudently extracted, it would still inadvertently serve the same original purpose (inhibit microbial growth or rather prevent microbial survival). Therefore, for these extracts to be harnessed, the particular regions of the plant where the defenses are stationed or most concentrated should be recognized. These regions are characterized often by eccentric tastes (stems) or colorfulness (leaves).The inclining principle is that for the intricacies of plants to be sterile, they must have “something” that keeps it that way. That “something” should be extracted and tested against certain microorganisms to discover the antimicrobial potencies. Interestingly, African mango (Irvingia gabonensis) leaf and root extracts have documented inhibitory activity against several bacterial and fungi (Kubmarawa et al., 2012). For instance, leaf extract of lrvirgia gabonensis used as a febrifuge. In Cameroon, preparation mainly from the bark are used to treat hernia and yellow fever and as an antidote for poisoning. Kernels of Irviginia gabonensis are used to treat diabetes. Preparations from the bark are rubbed on to the body to relieve pains and are applied to sores and wound and against toothache. They are also taken to treat diarrhea (Harris, 1996). Potential mechanism of action include membrane disruption by terpenoids and inactivation of microbial adhesion, enzymes and cell envelope transport proteins by ellagic acid-like compounds (Kuete et al., 2017). Dialium guineense is reported to possess antimicrobial activities in the cure of diarrhea, palpitations as well as fever (Lamien et al., 2010). Okwu and Ekeke (2003) reported in their studies that the plant contains saponins which are presumed to add to the cleaning effect of teeth and at the same time prevent caries and plaques on the teeth of the user. D. guineense leaf and bark extracts have been reported by Orji et al.,(2012) to show antimicrobial properties against Staphylococcus aureus and Klebsiella pneumoniae at varying concentrations. The antibacterial activities of both the aqueous and ethanolic leaf and bark extracts of D. guineense were evaluated while the phytochemical analysis reveals the presence of flavonoids, alkaloids, tannin and saponin. Also, the methanolic crude leaf extract of D. guineense was found by Akinpelu (2011) to possess bioactivity against fourteen out of eighteen environmental strains of Vibrio species. Phytochemical analysis of the plant extract revealed some phenolic compounds. These phenolic compounds include phenolic acids, flavonoids, tannins, saponins and cardiac glycosides among others. Phenolic compounds from medicinal herbs and dietary plants play important roles in health in addition to enhancing antimicrobial activities in these plants. D. guineense stem is used as chewing stick (indigenous tooth brush) among the Nigerian populace.

Oral infections caused by microorganisms have led to increased risk of oral health problems such as Dental Caries (DC), periodontitis and Oral Candidiasis (OC). Streptococcus mutans and Candida albicans are the primary organisms responsible for DC and OC, respectively. It has been demonstrated that the initiation and progression of oral disease is primarily due to the increased proliferation of opportunistic microorganisms (Gazim et al., 2008). A large variety of microorganisms are associated with oral disease, however, the increased proliferation of S. mutans , present in carious lesions, is the primary cause for the initiation and the progression of DC, and hence is of primary interest in the presented research (Gazim et al., 2008; Mojab et al.,2008). The relationship between this causative organism and pathogenesis is not clear, although it has been suggested that S. mutans proliferation leads to acid production, promoting tooth decay and DC (Kuete et al., 2017). OC, also termed thrush, is a yeast infection of the genus Candida, most often caused by C. albicans. The current methods for minimizing the incidence of DC focus on prevention techniques such as proper oral hygiene, drinking water fluoridation and application of dental sealants (Singleton, 1999). Unfortunately, as the statistics suggest, these prevention methods have shown only limited success. OC is typically controlled by anti-fungal drugs such as amphotericin B (Vogt, 2005). If not established as a biofilm, C. albicans is usually susceptible to most anti-fungals, but mechanical disruption of a biofilm prior to anti-fungal application may be required. A well-known problem is that long-term exposure to anti-fungal agents promotes acquired resistance (Bentley and Maganathan, 1982). The documented levels of resistance in oralCandida are indeed on the rise (Bentley and Maganathan, 1982). To address these shortcomings, an alternative therapy is necessary for controlling the incidence of DC and OC.

1.2 STATEMENT OF PROBLEM

High resistance of microorganisms to antibiotics.
High prevalence of Candida albicans and Streptococcus mutans with oral infection.
Lack of adequate research of Nigerian medicinal plants in the treatment of oral infection.

1.3 AIMS AND OBJECTIVES

AIM

The aim of this study is to determine the antimicrobial effect of two ethnobotanical Nigerian plants Dialium guineense (“Icheku”) and Irvingia gabonensis (“Ujiri”) against two microorganisms (Streptococcus mutans and Candida albicans) associated with oral infection.

OBJECTIVES

To determine the antimicrobial sensitivity of Dialium guineense(“Icheku”) and Irvingia gabonensis (“Ujiri”) against Streptococcus mutans and Candida albicans using agar well diffusion method.
To determine the minimum inhibitory concentration and minimum bactericidal concentration of Dialium guineense (“Icheku”) and Irvingia gabonensis (“Ujiri”) against the test organisms
To determine the phytochemical properties of Dialium guineense (“Icheku”) and Irvingia gabonensis (“Ujiri”)