A proteinaceous antimicrobial compound isolated from Marinobacter pelagius, exhibits antagonistic activity against...

Antimicrobial resistance (AMR) poses a serious threat currently to human health and necessitates urgent discovery of novel antimicrobial agents. We hypothesized that the vast biodiversity of the marine environment represents a promising resource for isolating bacteria with potent antagonistic activity against multi-drug resistant pathogens. The primary objective was to purify and characterize the antibacterial protein fractions exhibiting antagonistic activity from marine bacteria. To accomplish this, the present study isolated, identified, and characterized antibacterial compounds produced by bacteria from samples collected at Narara beach, Gujarat, India. Thirty-four bacterial isolates were obtained and screened for antagonistic activity against two multidrug-resistant (MDR) pathogens, Salmonella paratyphi and Acinetobacter baumannii. One isolate, ISD30, identified as Marinobacter pelagius by morphological, biochemical and 16 S rRNA gene sequencing, showed significant antagonistic activity. The 16 S rRNA gene sequence was deposited to GenBank, with accession number: PQ097291. The bioactive compound from M. Pelagius (ISD30) was confirmed as proteinaceous and purified using Fast Protein Liquid Chromatography (FPLC) gel filtration. FPLC yielded two bioactive fractions, one among them exhibiting potent antagonistic activity against MDR pathogen S. paratyphi, but not A. baumannii. SDS-PAGE analysis estimated the protein's molecular weight to be ~ 75 kDa. Upon analysis, the protein demonstrated a Minimum Inhibitory Concentration (MIC) of 70 µg/mL and thermal stability up to 70 °C. This study is the first report of an antibacterial protein from M. pelagius, with significant inhibitory activity against the MRD clinical pathogen S. paratyphi, highlighting the potential of marine Marinobacter species as a novel source for antimicrobial agents against MDR pathogens.