Antibacterial Activity of Soil Bacteria against Escherichia coli and GC-MS Analysis of their Organic Compounds

Antimicrobial agents encompass a wide range of compounds, including antibiotics, bacteriocins, and lipopeptides, which play a crucial role in combating infectious diseases. Antibiotics, in particular, are secondary metabolites of low molecular weight predominantly synthesized by soil dwelling microorganisms. These microbial metabolites have long served as a vital source of clinically important therapeutic agents. Members of the genus Bacillus and other rhizosphere-associated bacteria are especially known for producing diverse antimicrobial substances. In this study, ten rhizosphere soil samples were collected from different sites in Sana’a city, Yemen. From these samples, 50 antibiotic-producing soil bacteria were isolated. Bioactive metabolites were extracted using the solvent extraction method with chloroform and Ethanol. The crude extracts were analyzed by Gas Chromatography–Mass Spectrometry (GC–MS) to identify their organic composition. Among the 50 bacterial isolates, 14 showed antibacterial activity against resistant Escherichia coli using the agar well diffusion method. Further secondary screening revealed that the filtrates of four isolates Pseudomonas fluorescens, Bacillus subtilis, Acinetobacter baylyi, and Azotobacter vinelandii exhibited the strongest antibacterial effects. GC–MS analysis showed that each isolate produced more than eighty organic compounds; however, only a subset demonstrated antibacterial activity. The most notable bioactive compounds detected included Phenol, 4-(2-aminoethyl)- (CAS: tyramine), 2,4-di-tert-butylphenol, and n-hexadecanoic acid. This study highlights the potential of rhizosphere soil bacteria as promising sources of novel bioactive compounds. The identification of active metabolites and their antibacterial properties against resistant E. coli underscores their possible application in the development of alternative therapeutic strategiesto address antibiotic resistance.