Identification of Antibiotic in Ethyl Acetate Fraction Produced by A Local Isolate PLS 80 Isolated from Shallow Sea Fumaroles

The need for the discovery of new compounds with antimicrobial activity is increasing as triggered by the resistance of pathogen microorganisms to the current drugs. Simultaneously, interests are growing in exploiting extremophiles to find new active organic compounds. A thermo-halophilic bacterium (dubbed PLS 80), previously isolated from underwater fumaroles, could produce antibiotic. Hence, the objectives of this study were to study the inhibition activity and identify the structure of the antibiotic partially. PLS 80 isolate was grown on TSB medium, and the supernatant was sequentially partitioned with n-hexane, ethyl acetate, and methanol. The extracts were tested for antimicrobial activity by the disc-diffusion antibiotic susceptibility test. The extract with the highest activity was identified for their antibiotic class by chemical reactions using ninhydrin, iodine vapor, and potassium iodine. It was then purified using column chromatography using silica G-60, and the pure substance was subjected to GC MS analysis. Ethyl acetate fraction showed the highest inhibition zone, even higher compared to the Gentamicin control. The qualitative identification by the chemical reactions showed that the antibiotic could be of the β-lactam group. The mass spectrum data indicated that the ion fragments could be derived from benzylpenicillin. The antibiotic has a potential to be studied further, particularly to elucidate the structure entirely. Eventually, structural modifications can be conducted to produce potent antibiotics to overcome antibiotic-resistant microorganisms.