Orange-pigmented Paracoccus marcusii, symbiotic with the coral Favites sp., shows antibacterial properties against multidrug-resistant (MDR) clinical samples

The increasing prevalence of multidrug-resistant (MDR) bacteria presents a critical challenge in clinical settings, prompting the search for novel antibacterial agents. Orange-pigmented marine bacteria, strain NOE18, were isolated from coral Favites sp. on Kartini Beach, Jepara, Central Java, Indonesia, and cultured in the laboratory. The aim of this research includes molecular identification of strain NOE18, extracting orange pigment from strain NOE18, and investigating the antibacterial efficacy of orange-pigmented NOE18 against MDR clinical isolates. Strain NOE18 was identified as Paracoccus marcusii based on 16S rRNA gene sequence analysis. Its orange pigment was extracted using methanol and methanol:acetone (7:3), characterised by LC-HRMS, and evaluated for antibacterial activity against multidrug-resistant (MDR) clinical isolates using the microdilution method. The pigment exhibited antibacterial activity against all tested MDR isolates, with minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of ≥25 mg/mL and ≥50 mg/mL, respectively. LC-HRMS analysis identified canthaxanthin, adonirubin, and 3-hydroxy-3′-oxo-β,ε-carotene as the dominant carotenoids, which are likely responsible for the observed antibacterial activity. The findings suggest that Paracoccus marcusii, as a symbiont of Favites sp., possesses notable antibacterial properties against MDR pathogens. This underscores the potential of marine-derived bacteria as sources for developing new antimicrobial agents. Further investigation is needed to evaluate the mechanisms of action of specific compounds.