Crude extract from a hardcoral-associated bacterium Virgibacillus salarius PHC-44-04 inhibiting growth of Multidrug-Resistant Enterobacter aerogenes human pathogen

Abstract

Abstract. Ayuningrum D, Muchlissin SI, Trianto A, Radjasa OK, Sabdono A. 2020. Crude extract from a hardcoral-associated bacterium Virgibacillus salarius PHC-44-04 inhibiting growth of Multidrug-Resistant Enterobacter aerogenes human pathogen. Biofarmasi J Nat Prod Biochem 18: 82-87. Hardcoral-associated bacteria are potential sources of natural product compounds with a wide range of activities, i.e., antibacterial activity, antiviral, anticancer, antifungal, etc. Virgibacillus salarius PHC-44-04 is a gram-positive bacterium isolated in prior research from hard coral Pavona sp. collected from Panjang Island, Jepara, Indonesia. This bacterium at the screening phase was showing high antibacterial activity against Multidrug-Resistant Enterobacter aerogenes (MDR-EA). Therefore, this paper has aim to deliver the result of the crude extract antibacterial test from V. salarius PHC-44-04 after being cultivated in a liquid medium, to know the efficiency of using supernatant and pellet extract, and to determine in which concentration was the minimum for antibacterial activity. The cultivation of bacterial isolates was using liquid medium Nutrient Broth, and the production of crude extract was using the liquid-liquid extraction method. The liquid medium containing bacterial cells were separated using a centrifuge at 8,000 rpm and became supernatant and pellet. The supernatant was extracted using ethyl acetate, while the pellet was extracted using methanol. The antibacterial test from both crude extract from supernatant and pellet was using disk diffusion method with several concentration as follows: 15 µg/mL, 30 µg/mL, 60 µg/mL, 90 µg/mL, 180 µg/mL, 250 µg/mL, 350 µg/mL, and 500 µg/mL. Each concentration was repeated in three replicates. The crude extract produced from 700 mL supernatant was 0.0667 g and from 50mL pellets was 0.0320. The pellet crude extract has a higher mass but does not have antibacterial activity against MDR-EA. The result showed an only supernatant crude extract of V. salarius showed antibacterial activity against the MDR-EA bacterium. The minimal crude extract concentration to inhibit the growth of MDR-EA was 60 µg/mL. Meanwhile, the best concentration for exhibiting antibacterial activity was 500 µg/mL with a zone of inhibition (ZOI) diameter of 11.77 ± 0.8730 mm. Thus, supernatant should be the main source of crude extract production rather than the pellet to get high antibacterial activity.