Introduction

Medicinal plants may be defined as any plant that can be put to culinary or medicinal use and include those we associate with, orthodox drugs such as fox glove and opium poppy, as well as everyday plants, such as garlic₁.We shall not forget that all drugs of the past were substances with a particular therapeutic action extracted from plants. More and more researchers find that food and their individual constituents perform similar fashion to modern drugs and sometimes better without the dreaded side effects₂. The use of herbs and medicinal plants as the first medicines is a universal phenomenon. Every culture on earth, through written or oral tradition, has relied on the vast variety of natural chemistry found in healing plants for their therapeutic properties₂.

The onion is one of the oldest cultivated vegetables in history. It is thought that bulbs from the onion family have been utilized as a food source for Millennia. Onion consists of its herbaceous plant part and its edible bulb part. It is probably a native to southwestern Asia₃.The leaves are bluish –green and hollow. The bulbs are large, fleshy and firm. There are three main varities- white, red and purple skinned₄.The relative pungency of onion has both genetic and environmental components. Sulphur compounds in onions have also been shown to be anti-inflammatory both by inhibiting formation of thromboxanes and by inhibiting the action of platelet-activating factor (PAF). Thiosulfinates condition anti-thrombotic benefits, including antioxidant activity₅,₆, reduced serum cholesterol and enhance in vitro platelet activity ₇. This later effect is important for cardiovascular health by reducing the probability that platelets aggregate in the blood, a major cause of heart attacks and strokes.₈ Hence, thiosulphinates found in onion have been shown to inhibit in-vitro platelet aggregation₉,₁₀.

Flavonoids are a second class of health enhancing compound produced by onions, an example is quercetin. Flavonoids are chemical compounds active against microorganisms. They have been found in-vitro to be effective antimicrobial substance against a wide array of microorganisms ₁₁.Ginger, consists of the fresh or dried roots of Zingiber officinale. In humans, ginger is thought to act directly on the gastrointestinal system to reduce nausea ₁₂. Traditionally, ginger has been used to treat intestinal infections, especially related with digestive problems. Equally, its antibacterial ‘power' is effective against preventing numerous intestinal problems that take place as a result of the alteration of the intestinal flora. This is ideal to avoid the formation of ulcers by eliminating the Helicobacter pylori, a bacterium whose secretions of ammonia are responsible for many ulcers, especially those of the duodene, and for other stomach problems like gastritis, since the plant is able to neutralize the excess of gastric acid that is another of the causes that favours the formation of ulcers ₅.

The gingerols have analgesic, sedative, antipyretic, antibacterial and gastrointestinal tract motility effects. Ginger has the capacity to eliminate harmful bacteria, such as Escherichia coli, responsible for most of the diarrhoea, especially in children ₁₃. Ginger eases both diarrhoea and constipation; hence it should have impact on the growth of Bacillus cereus, which mainly causes diarrhoea and nausea. It has been shown to reduce the stickiness of blood platelets, hence may help reduce risk of artherosclerosis ₁₃,₁₄.

The genus Salmonella is among the most common causes of food and water borne infectious diseases in the world₁₅. The organism has a wide host range which comprises most animal species including mammals, birds and cold-blooded animals in addition to human. A number of studies in Nigeria have shown that Salmonella infections is endemic in many parts of the country₁₆,₁₇ and its endemicity increases especially in areas with low environmental hygiene₁₈,₁₉,₂₀,₂₁.

Bacillus subtilis has been implicated in various food spoilage including ropiness in bread, production of CO2 in canned meats, sliminess and coagulation in milk, e.t.c.₂₂.

Escherichia coli is one of the main causes of both nosocomial and community-acquired infections in humans and one of the micro-organisms most frequently isolated from blood. E. coli in humans is a common inhabitant of the gastrointestinal tract. It can also cause various intestinal and extra-intestinal diseases₂₃.The pathogenic isolates of E. coli have a relatively large potential for developing resistance₂₄,₂₅. The spread of microbial drug resistance is a global public health challenge, which impairs the efficacy of antimicrobial agents and results in substantial increased illnesses and death rate, hence, this work was therefore undertaken to investigate as well as authenticate the antimicrobial potentials of the two medicinal plants₂₆,₂₇.

Materials And Methods

Test Organism Confirmation

Collection And Identification Of Plant Materials

Extraction Of The Plant Materials

Preparation Of McFarland Standard

Innoculum Preparation By Direct Colony Suspension Method

Antimicrobial Screening Test

Results

The results of the antimicrobial properties of the extracts on the test organisms are shown in tables below:

Figure 1

Table 1: Sensitivity pattern of to raw onion juice

Figure 2

Table 2: Sensitivity pattern of to cold-water extract of onion.

Figure 3

Table 3: Sensitivity pattern of to hot-water extract of onion.

Figure 4

Table 4: Sensitivity pattern of to ethanolic- extract of onion.

Figure 5

Table 5: Sensitivity pattern of to raw ginger extract.

Figure 6

Table 6: Sensitivity pattern of to cold-water extract of ginger.

Figure 7

Table 7: Sensitivity pattern of to hot-water extract of ginger.

Figure 8

Table 8: Sensitivity pattern of to ethanolic extract of ginger.

Discussion

The result of this work indicates that the various soluble extracts of onions and ginger have antibacterial properties. When the extracts were tested on Escherichia coli, Salmonella typhi and Bacillus subtilis, the widest zones of inhibition was obtained with Salmonella typhi followed by Escherichia coli. These differences in the zones of inhibition may be directly related to the susceptibility of each test organisms to the onions and ginger extracts. The factors responsible for this high susceptibility of Escherichia coli and Salmonella typhi to the extracts are not exactly known but may be attributed to the presence of secondary plant metabolites₃₁.

It was clear from this work that the solvent of extraction affected the degree of antibacterial activity of the extracts. It was observed that the ethanolic extract of ginger gave the widest zone of inhibition (20mm) using the concentration of 0.8gml^-1 while the ethanolic extract of onion gave 9mm with 0.8mgl^-1 each against Salmonella typhi . This credit to ethanol extraction was supposed to ethanol being an organic solvent and will dissolve organic compounds better, hence liberate the active component required for antimicrobial activity₁₁.

It was also observed that raw onion and ginger extracts had activity only on Salmonella typhi and no effect on Escherichia coli and Bacillus subtilis. The reason for this is not clear because the raw juice is thought to be more concentrated than the other extracts since the growth of Escherichia coli and Bacillus subtilis was not inhibited at all. The hot water extracts of onions did not inhibit the growth of Salmonella typhi. This may be explained by the fact that the antimicrobial substance in the onion extracts, which are mainly phenolic compounds are destroyed by heat from the hot-water which might have raised the temperature of the extracts inactivating them₃₂. In general, antibacterial components in the spice plants are heat-labile; hence all the spices lost their antibacterial activities within 20minutes at 100°C₃₂. Since, the hot- water extract of ginger showed activity on Salmonella typhi, the reason for this variation is not very clear. The cold-water extract of onion did not inhibit at all the growth of Escherichia coli and Bacillus subtilis but inhibited Salmonella typhi at 0.8gml^-1 while the cold-water extract of ginger inhibited both Escherichia coli and Salmonella typhi at all concentrations. It could be said that cold-water as an extractant could liberate the active constituents of ginger better compared to onions. It was similarly observed that the extracts inhibited the growth of the two gram-negative test organisms Escherichia coli and Salmonella typhi to a reasonable degree though not completely but had no observable effect on the gram-positive organism Bacillus subtilis, hence, the two susceptible bacteria are responsible for various stomach related illnesses such as typhoid fever, diarrhoea and gastroenteritis₃₃.

It is worthy to note that the antimicrobial activities of these plants extracts were dependent on the concentration of the extracts as reported by₁₁. Also, if the extract has high molecular weight, the rate of diffusion is always slow, reduced and also takes longer time, whereas an extract of low molecular weight diffuses faster and at a quicker rate. The result obtained is evidence that Zingiber officinale (ginger) produced marked inhibitory effect on the two test organisms compared to Allium cepa (onions). Hence, it has been reported that ginger extract and its pungent compounds demonstrated greater antibacterial activity against a variety of bacterial species including Helicobacter pylori, Staphylococcus aureus, Pseudomonas aeruginosa and Escherichia coli, although mixed result is attributed to different ginger preparations and varying strength₃₄.