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Extended-spectrum β-lactamase (ESBL)-producing bacteria pose a big challenge in clinical practices, warranting a new therapeutic strategy. In this study, methanol extract of the marine cyanobacterium Oscillatoria acuminata NTAPC05 was fractionated under bioassay guidance and the fractions were tested against three well-characterized ESBL-producing bacteria Escherichia coli U655, Stenotrophomonas maltophilia B929 and Enterobacter asburiae B938. Out of the four HPLC fractions, fraction 2 showed bactericidal activity against all the three ESBL producers much more efficiently (MIC 100 μg ml) than the fourth-generation cephalosporin (MIC >125 μg ml). The active fraction was subjected to time-kill test at concentrations of 1/2 × MIC, 1 × MIC and 2 × MIC, and the results substantiated the bactericidal property of the fraction against the ESBL producers. Spectral analysis revealed monogalactosyldiacylglycerol containing a palmitoyl (MGDG-palmitoyl), being reported for the first time, as the active fraction, and its bactericidal property against ESBL producers was determined. The active fraction appears to damage the bacterial membrane leading to lysis of the cell, as revealed in confocal laser scanning microscopy (CLSM) analysis, that was confirmed in scanning electron microscopic analysis. Cytotoxicity assay revealed the O. acuminata compound to be safe to a normal cell line HEK293 (human embryonic kidney cell). The in silico analysis of MGDG-palmitoyl revealed two successive H-bonding interactions with Leu198 of TEM1 β-lactamase. Taken together, the MGDG-palmitoyl from O. acuminata NTAPC05 offers potential to develop analogs as a therapeutic for bacteremia caused by ESBL producers.

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Objective: The present investigation aimed at the screening of pharmaceutically potential antimicrobial metabolite isolated from marine Micromonospora sp. to combat the multidrug‑resistant bacteria. Materials and Methods: The Marine sediments were randomly collected for the isolation of Micromonospora sp., from Gulf of Mannar, East Coastal Region, located at Kayalpatnam, Tuticorin district, Tamil Nadu, India. The Micromonospora sp. was cultivated by serial dilution and crowed plating method on actinomycetes isolation agar. The isolated colonies were identified by morphological, cultural, and biochemical methods. The antibacterial study of Micromonospora sp. was performed on Mueller‑Hinton agar medium against multidrug‑resistant bacteria isolated from urinary tract infection. The antibacterial compound was separated and characterized by Fourier‑transform infrared (FT‑IR) and nuclear magnetic resonance (NMR) spectrum. Results: Based on the morphological, cultural, and biochemical studies, the isolated colonies were found to be the genera of Micromonospora. Among Micromonospora genera, Micromonospora marina KPMS1 strain showed potent antibacterial activity against multidrug‑resistant Escherichia coli, Pseudomonas aeruginosa, and Enterococcus faecalis. The FT‑IR and NMR studies showed the structural elucidation of active compounds derived from M. marina KPMS1. The 16S rRNA sequences of M. marina KPMS1 (MH036351) strain were blasted and deposited in the GenBank of National Center for Biotechnology Information. Conclusion: The results of the study were concluded that microbial compounds are the promising sources of nearly all of the antibiotics produced by marine Micromonospora sp. The detection of new biological compounds was considered to represent a novel species of the genus Micromonospora which have been used for clinical treatment against multidrug‑resistant bacteria and were pharmaceutically important.

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