en Anti-microbial agents, resistance and treatment protocols Anti-microbial agents, resistance and treatment protocols Original article Original article <div style="text-align: justify;"><b><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">Introduction: </span></span></span></b><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">Hospital-acquired infections caused by <i>Pseudomonas aeruginosa</i> strains frequently exhibit resistance to both monotherapy and combination therapy with antibiotics because of acquired and intrinsic resistance mechanisms. Therefore, there is an urgent need for novel and potent antibiotics to treat infections caused by multidrug-resistant (MDR) <i>P. aeruginosa</i>. Bioactive compounds from marine <i>Bacillus</i> species have the potential to inhibit the growth of MDR <i>P. aeruginosa</i></span></span></span><span lang="EN-IN" style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">. <b>Methods:</b> </span></span></span><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">In the present investigation, a <i>Bacillus</i> species was isolated from seawater using Zobell Marine Agar. The isolate was identified by morphological, biochemical, and 16S rRNA gene sequencing analyses. Ethyl acetate was used to extract extracellular bioactive secondary metabolites from the cell-free supernatant of the isolated strain. Column chromatography (silica gel, 100&ndash;200 mesh) was employed to further fractionate the crude extract, and the agar well diffusion method was used to assess antibacterial activity against MDR <i>P. aeruginosa</i>. The bioactive fraction F1 was putatively annotated using ultra-high-performance liquid chromatography&ndash;ultraviolet&ndash;mass spectrometry (UHPLC-UV-MS)</span></span></span><span lang="EN-IN" style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">. <b>Results: </b></span></span></span><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">The marine bacterial isolate was identified as <i>Bacillus amyloliquefaciens</i>. The crude extract and its purified fraction F1 inhibited the growth of MDR <i>P. aeruginosa</i>. The column chromatography&ndash;purified bioactive fraction F1 showed </span></span></span><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">zones of inhibition ranging from 15.0 to 16.7 mm against MDR <i>P. aeruginosa</i>. UHPLC-UV-MS analysis putatively annotated bioactive fraction F1 as stigmatellin Y, exhibiting a retention time of 28.50 min and a mass-to-charge ratio (<i>m/z</i>) of 507.2725 ([M+Na]⁺</span></span></span><span lang="EN-IN" style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">. <b>Conclusion: </b></span></span></span><span style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">This marine <i>B. amyloliquefaciens</i> strain produces the potent compound stigmatellin Y, which exhibits activity against MDR <i>P. aeruginosa</i>. This finding highlights the strain&#39;s potential as a source of novel therapeutic agents</span></span></span><i><span lang="EN-IN" style="font-size:10.0pt"><span style="line-height:107%"><span new="" roman="" style="font-family:" times="">.</span></span></span></i></div> Multidrug-resistant Pseudomonas aeruginosa, Stigmatellin Y, Marine Bacillus amyloliquefaciens, UHPLC-UV-MS 130 136 http://jommid.pasteur.ac.ir/browse.php?a_code=A-10-680-1&slc_lang=en&sid=1 Bhagvat Lad ladbhagvat123@gmail.com 0009-0005-5302-641X Yes School of Life Sciences, Swami Ramanand Teerth Marathwada University, Nanded, 431606, Maharashtra, India Sanjay Chavan sanjaychavan5551@gmail.com 0009-0005-4221-7827 No School of Life Sciences, Swami Ramanand Teerth Marathwada University, Nanded, 431606, Maharashtra, India T.A. Kadam takadam67@gmail.com 0000-0002-5982-8983 No School of Life Sciences, Swami Ramanand Teerth Marathwada University, Nanded, 431606, Maharashtra, India.