Evaluation of Antimicrobial Activity in Enterobacter, Paenibacillus and Brevibacillus Species Isolated in Soil Samples From Lakes Magadi, Bogoria and Elementaita

Abstract

Species of genera Enterobacter, Paenibacillus and Brevibacillus are widely distributed throughout the globe and they have been isolated in different habitats i.e. soil, saline and alkaline water bodies, decaying plant materials, clinical materials and from the gut of animals and human microbiota. Most species of these genera are known to produce antimicrobial secondary metabolites with wide application in pharmaceutical, agricultural and food industries. The emergence of pathogenic microorganisms with multiple drugs resistance has raised the need to find more alternatives of potential active biological compounds from natural resources. In this study, various species of genera Enterobacter, Paenibacillus and Brevibacillus were isolated in soil samples from Lakes Magadi, Bogoria and Elementaita, characterized and tested for their antimicrobial activity against various pathogenic microorganisms with the aim of finding new antimicrobial compounds. Twenty-four isolates of these genera were isolated and fermented in CY broth with amberlite XAD 16 (adsorbent resin) for 7 days at 30o C. The antimicrobial compounds were extracted using methanol and concentrated in rotary evaporator. Nine isolates presented antimicrobial activity against test pathogenic bacteria (Salmonella spp., E. coli, Pseudomonas spp., K. pneumonia, S. aureus and L. monocytogenes). Isolates Enterobacter sp. strain MC dung, Enterobacter sp. strain BC dung, Brevibacillus sp. Strain BC/5BC, FU78CB, Enterobacter sp. strain FU 103BA and Brevibacillus sp. strain ELHPS3H13 expressed broad spectrum against the test pathogenic bacteria while Paenibacillus sp. Strain FU 75 BC, Enterobacter sp. FU 104C and BC5AC showed narrow spectrum against Gram-negative bacteria (Salmonella spp., K. pneumonia, Pseudomonas spp., and E. coli). Among the isolates, Enterobacter sp. strain BC dung had significantly (P< 0.05) higher antibacterial activity against Pseudomonas spp. (Md=16mm), S. aureus (Md= 35mm), Listeria monocytogenes (Md= 34mm) and K. pneumoniae (Md =30mm). The morphological, biochemical and molecular characterization revealed that isolates BC dung, MC dung, FU 104 C and FU 103 BA belong to genus Enterobacter, BC/5BC and ELHPS3H13 belong to genus Brevibacillus, while isolates FU 75 BC, FU 78CB and BC5AC belong to genera Paenibacillus, Providencia and Lysinibacillus respectively. The isolated species of genera Enterobacter, Paenibacillus and Brevibacillus possessed antimicrobial compounds which were active against the selected pathogenic bacteria.