Diarrhoeal diseases still remain a public-health problem in developing countries (1,2). In Nigeria, shigellosis is endemic in most communities. Severe infections initially seen in children aged less than five years are now frequently occurring among adolescents and young adults (3,4). This observation emphasized the need of better treatment, preferably using simple but useful local ingredients and herbs.
The medicinal plants, including Ocimum gratissimum (Lamiaceae), Momordica balsamina (Curcibitaceae), and Terminalia avicennoides (Combretaceae) are abundantly grown in Nigeria and are used in folk medicine for treating ailments, including various digestive disorders, and asthenia (5). The essential oil obtained from the seeds of O. gratissimum contains thymol and eugenol in amounts ranging from 32% to 65%. These substances are antiseptic, antitussive, and antispasmodic in functions (6). Ilori et al., Akinsinde and Olukoya, and Akinyemi et al. have shown that the extracts of leaf and bark of these plants possess antidiarrhoeal properties (7-9). However, the effects of these compounds on specific pathogens, such as shigellae, are not known. It is, thus, important to determine the antibacterial effects of these compounds against shigellae, specifically multidrug-resistant Shigella infections that have been so common in the country during the last 10 years (10).
In the present study, we have examined the antibacterial activities of decoctional and concoctional preparations of three plants: O. gratissimum (Lamiaceae), M. balsamina (Curcibitaceae), and T. avicennoides (Combretaceae) against Shigella species isolated from stools of patients with bacilliary dysentery.
MATERIALS AND METHODS
Fresh leaves of O. gratissimum and M. balsamina detached from their stems and the stem-bark of T. avicennoides purchased from a local market in Lagos were used in this study. The plants were vouchered as Morb-002, Ogr-010, and Tav-005 after authentication at the Botany Department of Lagos State University, Nigeria.
Preparation of extracts
Aqueous extracts of the plants were prepared according to the method of Olukoya et al. (11). Seventy gram each of dried, grinded leaves and 50 g of powdered stem-bark were soaked separately in 200 mL of autoclaved water for seven days at 30.32 ¢°C under sterile conditions. The extracts were filtered through a millipore filter (0.25 ¥ìm). The resulting filtrate was concentrated under reduced pressure at 50 ¢°C and then transferred to a labelled sterile bottle.
Four isolates each of Shigella dysenteriae, S. flexneri, S. boydii, and S. sonnei recovered from the stools of patients with shigellosis in Lagos, Nigeria, were screened. All the isolates were sensitive to ofloxacin but showed .75% resistance to tetracycline, co-trimoxazole, streptomycin, colistin sulphate, ampicillin, and streptomycin.
An inoculum of size 108cfu/mL of each of the isolates was prepared according to the method of Bauer et al. (12). A loopful (0.002 mL) of each inoculum corresponding to 1x105cfu per plate was streaked evenly on Mueller-Hinton agar (Difco, USA). The plates were dried in the air and then mounted with ofloxacin disc (5 ¥ìg), and discs were pre-soaked with crude extracts of the medicinal plants (3,000 ¥ìg/mL). Another inoculum (similar size) of Escherichia coli ATCC25922 was also used on Mueller- Hinton agar to serve as a negative control. The inoculated plates containing discs pre-soaked with sterile water served as positive control. All the plates were incubated aerobically at 37 ¢aC for 24 hours. Diameters of zones of inhibition were measured in mm and recorded.
Minimum inhibitory concentrations
Decoctions and concoctions of the extracts were tested for shigellocidal activity using the macrobroth dilution method. Each decoction was diluted with Mueller-Hinton broth to yield concentrations of 1,500, 750, 375, 300, 187. …