Screening actinomycetes associated with lemon grass (cymbopogon citratus) rhizosphere for activity Against multi drug resistant bacteria

Abstract

Globally, there is increasing demand for novel bioactive molecules to combat the upsurge of multiple antibiotics resistant pathogenic bacteria. Consequently, researches are now directed towards different environments to identify microorganisms with capability of producing new, potent and safe compounds. In this study, sixty Actinomycetes isolates obtained from the rhizosphere of lemon grass were screened for antibacterial substance production using thirty-four multiple antibiotic resistant bacteria isolates isolated from soils obtained from dumpsites in Abraka metropolis, Delta State. Out of the 60 Actinomycete isolates, 6 (10%) belonging to the genus Streptomyces demonstrated antibacterial activity against at least one of the 34 test bacterial isolates. Although, 5(83.3%) out of the 6 Streptomyces spp exhibited antibacterial activity against only the Gram positive test bacterium, 1(2.04%) coded as Str1, demonstrated broad spectrum activity. This resulted in the extraction of its secondary metabolites using ethyl acetate. There were no significant differences at p < 0.05 between zones of inhibition (ranging from 19 to 24 mm) produced against various test isolate by the crude extract and that produced by the antibiotics used as control (ceftriaxone) indicating susceptibility of the strains to the crude extract. Analysis of the extract using GC-MS, led to the identification of 25 compounds. However, the main constituent with suspected antibacterial activity were 1,2 benzodiol,3,5-bis(1,1-dimethylethyl)-, 2-methyl-7-phenyl indole, 2,4,6, cycloheptatrien-1-one3,5, -bis-tri-methylsilyl and benzo[h]quinolone,2,4-dimethyl. Hence, the study concludes that the Streptomyces sp Str1 produced compounds with antibacterial properties against both Gram positive and negative multiple antibiotics resistant bacteria and thus is a potential candidate for the development of promising antibacterial agents.