Cross-Species Induction and Enhancement of Antimicrobial Properties in Response to Gamma Irradiation in Exiguobacterium sp. HKG 126

Abstract

A gram positive, extreme haloalkaliphilic, radioresistant bacterium was isolated from mangrove region of Kerala (India) which was characterized as Exiguobacterium sp. HKG-126 using morphological, physiological, biochemical and molecular characterization. Present investigation was undertaken to examine Exiguobacterium sp. as a potential source of broad-spectrum antimicrobial activity and enhancement in this activity was observed due to crossspecies/cross-genera induction and also in response to high dose of gamma (c) irradiation. Individual studies on the antimicrobial activity of all the co-cultivated bacterial strains before and after mixed culture fermentation, showed excellent enhancement in antimicrobial activity of Exiguobacterium sp. against a variety of clinical pathogens. To the best of our knowledge, this is the first report showing existence of an extremely high radioresistant strain of (up to 15 kGy) Exiguobacterium sp.

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“…The minimal inhibitory concentration (MIC) was assessed by the broth microdilution method 18,19 . The synthesized compounds were weighed (10 mg) and dissolved in DMSO to prepare the stock solutions of 10 mg/mL.…”

Synthesis and antibacterial activity screening of quaternary ammonium derivatives of triazolyl pyranochromenones

“…synthesized compounds on bacterial growth was estimated, using Kirby-Bauer disc diffusion test with some minor modifications. 20,21 250 μg/disc concentration of the samples were impregnated on a 6 mm, sterile Whatman paper disc. The targeted test organisms were seeded before the sterile disc placed in the respective grid of each Mueller-Hinton agar plates.…”

“…Assay: Minimum inhibitory concentration assay was performed to quantitative evaluation of antibacterial actitivity by estimating the MIC of the compounds. 20,21 The bacterial strains were cultured overnight at 37 • C in nutrient broth and used as an inoculum. The wells of ELISA plate with various dilutions of the compounds (1-0.0001 mg/mL) were treated with 50 μL of inoculums (OD 600 = 0.4-0.6) of the relevant culture and incubated at 37 • C for overnight.…”

“…The antibacterial activity screening of all the synthesized quaternary ammonium derivatives (26-31) and their bromo-precursors (20-25) was carried out against four pathogenic bacterial strains i.e., two Grampositives Bacillus cereus and Staphylococcus aureus and two Gram-negatives Pseudomonas aeruginosa and Escherichia coli by disc diffusion assay performed at a concentration of 250 μg/disc (Table 1). 11,20,21 The screening results revealed that three of the six quaternary ammonium compounds (26-31), i.e., 27, 29, and 31 having a longer alkyl moiety (n = 10), exhibited excellent to moderate activity against two gram-positive bacteria (B. cereus and S. aureus) and a gram-negative bacterium (P. aeruginosa). All of these compounds developed a zone of inhibition (ZI) equal to or greater than 12 mm.…”

Homology Modeling and Comparative Profiling of Superoxide Dismutase Among Extremophiles: Exiguobacterium as a Model Organism

“…To gain a more comprehensive understanding about the role of SODs in various stress-responses, we selected Exiguobacterium sp., a gram positive extremophile which is tolerant towards high doses of gamma radiation, high salt stress conditions and has the inherent ability to grow within a temperature range of -2.5 to 40°C [9]. Exiguobacterium, like other extremophiles possesses a free radical scavenging activity due to the presence of antioxidants like glutathione, catalase and SODs [10].…”