In vitro assessment of the synergism between extracts of Cocos nucifera husk and some standard antibiotics

Objective: To evaluate the interactions between the crude extracts of Cocos nucifera (C. nucifera) and six front line antibiotics (ampicillin sodium salt, penicillin G sodium, amoxicillin, chloramphenicol, ciprofloxacin and tetracycline hydrochloride), against some bacterial pathogens linked with human infection. Methods: The pulverized husk of C. nucifera was dissolved in 95% n-hexane and extracted using Soxhlet extraction method and sterile distilled water (aqueous). The antibacterial susceptibility of the crude extracts of C. nucifera was tested against environmental and clinical strains (6) obtained from the South African Bureau of Standards (SABS), Vibrio (6) and Listeria pathogens (6). The agar-well diffusion method was used for screening the extracts for their antibacterial activity. The minimum inhibitory concentration and minimum bactericidal concentration of the extracts were determined. Time-kill assay was used to evaluate bactericidal and/or bacteriostatic activity. The synergistic effect of the crude extracts and antibiotics was assessed and evaluated by adopting the checkerboard methods. Results: With the time-kill assay, the highest bactericidal activity was observed on Vibrio fluvialis EL041 with a -5.6 +/- 0.2 log(10) CFU/mL decrease in cell density as a result of the combination of the extracts and chloramphenicol at two-fold minimum inhibitory concentrations. Synergisms using the time-kill assay constituted about 72%, while indifference constituted about 28%. The checkerboard method revealed synergistic interaction in 67% of the combinations, and indifference in 33%. There was no specificity in the observed synergy to a particular class of antibiotics. Conclusions: This investigation suggests the crude extracts of C. nucifera to be a potential broad spectrum antimicrobial compound. Therefore, further study is needed to isolate the pure compounds from these crude extracts.