Introduction

Pseudomonas aeruginosa is the epitome of an opportunistic pathogen of humans. The bacterium almost never infects uncompromised tissues, yet there is hardly any tissue that it cannot infect if the tissue defenses are compromised in some manner. Pseudomonas exploits most defenses to initiate an infection. It causes urinary tract infections, respiratory system infections, dermatitis, soft tissue infections, bacteremia, bone and joint infections, gastrointestinal infections and a variety of systemic infections, particular in patients with severe burns and in cancer and AIDS patients who are immuno-suppressed. Other diseases it causes are pneumonia, endocarditis, chronic lung infections and septicemia and the bacterium is the 4^th most commonly isolated nosocomial pathogen accounting for 10.1 percent of all nosocomial infections₁.

Staphylococcus aureus causes a variety of suppurative (pus-forming) infections and toxinoses in humans. Staphylococcus aureus causes superficial skin lesions such as boils, styes and more serious infections such as osteomyelities and endocarditis. It is the major cause of nosocomial infections of surgical wounds and infections associated with indwelling medical devices. Staphylococcus aureus causes food poison by releasing enterotoxins into food and toxic shock syndrome by the release of super antigens into the blood stream₂.

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 garlic₃. 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 effects₄. 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 properties₄.

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 Asia₅. The leaves are bluish –green and hollow. The bulbs are large, fleshy and firm. There are three main varieties- white, red and purple skinned₆. 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 activity₇,₈, reduced serum cholesterol and enhance in vitro platelet activity₉. 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 strokes₁₀. Hence, thiosulphinates found in onion have been shown to inhibit in-vitro platelet aggregation₁₁,₁₂.

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 microorganisms₁₃.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 nausea₁₄. 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 ulcers₇.

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 children₁₅. 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 artherosclerosis₁₅,₁₆.

Materials And Methods

Test Organism Confirmation

Collection And Identification Of Plant Materials

Extraction Of The Plant Materials

Ginger Extraction

Preparation Of McFarland Standard

Innoculum Preparation By Direct Colony Suspension Method

Antimicrobial Screening Test

Results

The results of the biochemical tests and the antibacterial activities of the extracts on the test organisms are shown in tables below:

Figure 1

Table 1: Biochemical characteristics of the test organisms

Figure 2

Table 2: Sensitivity pattern of and to raw onion juice

Figure 3

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

Figure 4

Table 4: Sensitivity pattern of and to hot-water extract of onion.

Figure 5

Table 5: Sensitivity pattern of and to ethanolic- extract of onion.

Figure 6

Table 6: Sensitivity pattern of and to raw ginger extract.

Figure 7

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

Figure 8

Table 8: Sensitivity pattern of and to hot-water extract of ginger.

Figure 9

Table 9: Sensitivity pattern of and to ethanolic extract of ginger.

Discussion

The result of this work indicates that the water-soluble extracts of onions and ginger have antibacterial properties. When the extracts were tested on Staphylococcus aureus and Pseudomonas aeruginosa, the widest zones of inhibition were obtained with P. aeruginosa. 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 P. aeruginosa to the extracts are not exactly known but may be attributed to the presence of secondary plant metabolites₂₀.

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 (22mm) using the concentration of 0.8gml^-1 while the ethanolic extract of onion gave 11mm with 0.8mgl^-1 each against P. aeruginosa. 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 activity₁₃.

It was also observed that raw onion and ginger extracts had activity only on P.aeruginosa and no effect on S.aureus. 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 S.aureus was not inhibited at all. The hot water extracts of onions did not inhibit the growth of Pseudomonas aeruginosa. 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 them₂₁. In general, antibacterial components in the spice plants are heat-labile; hence all the spices lost their antibacterial activities within 20minutes at 100°C₂₁. Since, the hot- water extract of ginger showed activity on P.aeruginosa, the reason for this variation is not very clear. The cold-water extract of onion did not inhibit at all the growth of S.aureus but inhibited P. aeruginosa at 0.8gml^-1 while the cold-water extract of ginger inhibited both organisms 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 is note worthy that the antibacterial activities of these plants extracts were dependent on the concentration of the extracts as reported by₁₃. 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 strength₂₂.