Activity of Antibiotic Producing Bacteria Isolated from Rhizosphere Soil Region of Different Medicinal Plants

Nedaa Khair

Qatar University, Qatar

Abstract: The present study was carried out to explore the production of antibacterial agents from rhizosphere soil bacteria of medicinal plants and determine their activity against Gram-negative (Pseudomonas aeruginosa, and Escherichia coli) and Gram-positive (Bacillus cereus, and Staphylococcus aureus) bacteria. Soil samples collected from rhizosphere region of 11 medicinal plants were used to isolate and characterize antibiotic producing bacteria (APB). Those isolates (108) were primarily tested using Cross-streak method against test bacteria. This further led to antibiotic susceptibility test (AST) using cell free supernatant (CFS) extraction from cultures of APB obtained in the production media. Moreover, combinatorial effect of isolates’ CFS with two organic acids (3% Acetic acid and 0.4 mg/ml Acetylsalicylic acid), two commercial antibiotics (0.016 mg/ml Augmentin and 0.128 mg/ml Doxycycline), and two pure antibiotics (10 mcg/disk Penicillin and 25 mcg/disk Carbenicillin) was in vitro evaluated using AST. Some of those combinations showed marked synergistic activity against test bacteria, specially CFS-Carbenicillin combinations, with variations in inhibitory zones. Additionally, the presence of acetic acid, lactic acid and citric acid in CFS of isolates APB was confirmed by HPLC analysis. Ultimately, in vitro antibacterial study for rhizosphere soil bacteria in this work suggests the possibility of using these bacterial metabolites in clinical infections caused by selected test bacteria, especially when they combine with antibiotics or organic acids.