Antibacterial Potential of Pseudomonas aeruginosa ISP1RL4 Isolated from Seaweed Eucheuma cottonii Against Multidrug-resistant Bacteria

Eucheuma cottonii is a type of seaweed that are commonly found in Indonesia. As many other marine organisms, E. cottonii builds a strong bonding with its endophytic bacteria. These bacteria are well known to synthesize various of bioactive compounds including antibacterial compounds to protect its host from bacterial infections and pathogenic bacteria. Previous study has successfully isolated bacterial encoded ISP1RL4 with antibacterial potential against nonresistant Gram-positive and Gram-negative bacterial target. This research aimed to identify the ISP1RL4 isolate based on DNA sequencing, to evaluate antibacterial activity of the crude extract of ISP1RL4 isolate against multidrug-resistant bacterial target and to analysis chemical profiling of the extracts. Briefly, the cell mass of ISP1RL4 bacterial isolate was fermented for 2 weeks in 100 mL sterile liquid ISP-2 medium and then filtered. Extraction was carried out using ethyl acetate with an extraction ratio of 1:1 twice. Ethyl acetate extracts of ISP1RL4 were tested against multidrug-resistant bacteria Methicilin-resistant Staphylococcus aureus (MRSA), Escherichia coli ESBL, Klebsiella pneumoniae ESBL, and Acinetobacter baumanii. Our findings revealed that the ISP1RL4 phylogenetically related to Pseudomonas aeruginosa strain M4 with 100% of sequence similarity. The crude extract of P. aeruginosa ISP1RL4 showed diameter zone of inhibition of 9.0±1.0 mm, 10.3±2.0 mm and 9.4±0.1 mm against MRSA, E. coli ESBL, and K. pneumoniae ESBL respectively. No antibacterial activity of the crude extract was observed against A. baumanii. The liquid chromatography-high resolution mass spectrometry (LC-HRMS) analysis detected 381 compounds with 2-Amino-1,3,4-octadecanetriol (11.2%) identified as the major antibacterial compound present in ethyl acetate extracts of P. aeruginosa ISP1RL4. In addition, gas chromatography/mass spectrometry (GC/MS) analysis identified 39 compounds and 11 of them have been associated as antibacterial molecules. Among these 11 molecules, four prominent antibacterial compounds (> 8%) were 2-hexanol, 3-hexanol, 3-Pentanol, 2-methyl- and 2-hexanone. Overall, the ability of P. aeruginosa ISP1RL4 crude extract to inhibit selected multidrug-resistant bacterial target and the presence antibacterial compounds in the extract provided a promising result that the isolate could potentially be a promising antibacterial producer.