Phytochemical analysis and antimicrobial activities of mangrove plant (Rhizophora apiculata) against selected fish pathogenic bacteria

Abstract

Rhizophora apiculata leaf extracts were tested on the isolated growth of S. agalactiae and E. coli and extraction of the bioactive compounds were performed using Soxhlet extraction technique with methanol (MtOH) as the organic solvent. The presence of various phytochemicals in bioactive constituents of the plant was detected using standard chemical procedures. The Kirby-Bauer test was used for the antibacterial assay, and an in vitro assay was conducted for minimum inhibitory concentration (MIC) and minimum bacterial concentration (MBC). Brine shrimp lethality assay evaluated the toxicity of R. apiculata. Antibiotic susceptibility test showed high rates of E. coli resistance to neomycin and sensitivity to tetracycline and amoxycilin, while S. agalactiae showed sensitivity to all antibiotics. Inhibition zones of R. apiculata leave extract against the microorganisms recorded in the range of 2-9 mm. Increasing the inhibition zone is dependent on increasing plant extract concentrations. The (MIC) testing range of R. apiculata was 6.25 mg/ml to 12.5 mg/ml against S. agalactiae and E. coli, respectively. The MBC/MIC ratio of S. agalactiae demonstrated to be bactericidal, and the MBC/MIC ratio of E. coli was bacteriostatic. R. apiculata recorded an LC50 value of 81 mg/ml. The findings of this study reveal the valuable metabolites found in mangrove leaves. The most important secondary metabolites are alkaloids, terpenoids and tannins as well as saponins and steroids, but not flavonoids. This study suggests that Rhizophora apiculata has the potential to be a valuable candidate in the discovery of antimicrobial compounds against fish pathogens.