With the rise of resistant bacterial pathogens, currently prescribed antibiotics are rendered useless. In recent years, marine natural products (MNPs) have emerged as novel sources for drug leads. The ocean is a complex environment where marine animals cohabitate with many, and sometimes harmful microorganisms and viruses, but resist infections. Developed defenses, specifically mucous on fish scales, has been found to contain a variety of immunological chemical defenses and host a diverse microbial community. Recently, cultures from the exterior fish microbiome has been found to inhibit growth of human and fish pathogenic bacteria and fungi.
In exploration for new antibiotics, bacteria were isolated from the mucous of Pacific fishes and screened for their antibiotic-producing potential. Mucous swabs from juvenile fish yielded 47 different microbial strains. Strains were grown and extracted with organic solvent to obtain chemical extracts. Extracts were tested in antimicrobial microbroth assays against Staphylococcus aureus, Escherichia coli, and Candida albicans at 125 µg/mL. Nineteen extracts yielded potent inhibitory activity in at least one assay. In a case study of a particularly potent extract (PF-1-D), three inhibitors against methicillin resistant S. aureus and one metabolite with moderate inhibition of colon carcinoma were identified. Metabolites were isolated using multiple chromatographic techniques and elucidated by nuclear magnetic resonance and mass spectrometry. Overall, the potent anti-infective activity of these strains showcase bioactive metabolites that can be found within the Pacific fish microbiome, a potentially untapped source of novel antibiotics.
Keywords: marine natural products, fish mucous, antibiotics, Pseudomonas sp., antimicrobial resistance