The present study dealt with the screening of soil bacteria with antibacterial activity from different locations in Bangalore, India. Antibiotics play the role of self-defense mechanism for the bacteria and are produced as secondary metabolites to protect themselves from other competitive microorganisms. The need for new antibiotics arose as the pathogenic bacteria acquire resistance to various antibiotics meant for treating human diseases. Given the importance of antibiotics of bacterial origin, standard techniques have been used to isolate and characterize the soil bacteria which showed antibacterial activity. The isolated bacteria were tested against human pathogenic bacteria like Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, and Klebsiella pneumoniae by primary and secondary screening methods. The isolates PR1, PR2, and PR3 were confirmed to have antibacterial activity against S. aureus, E. coli, P. aeruginosa, and K. pneumoniae by both methods. Studies on the effect of filter sterilization, autoclaving, and proteinase K treatment on culture filtrates showed filter sterilization as the best method. The effect of different carbon and nitrogen sources on the antibacterial activity showed that preference by each isolate differed for carbon and nitrogen requirements. The isolates PR1, PR2, and PR3 were identified as Bacillus aryabhattai strain PR-D07, Arthrobacter humicola strain PR-F07, and Neomicrococcus lactis strain PR-F11 through 16S rRNA sequencing. Findings from this research work are encouraging and could proceed further to applied aspects. Only 3 bacterial isolates out of 263 isolates from soil samples displayed antibacterial activity against human pathogens S. aureus, E. coli, P. aeruginosa, and K. pneumoniae. They were identified as B. aryabhattai, A. humicola, and N. lactis by 16S rRNA studies and all of them are Gram-positive. Each isolate preferred different carbon and nitrogen sources for their enhanced antibacterial activity. Efficacy of the culture filtrates of these isolates was tested by filter sterilization, autoclaving, and proteinase K treatment. Filter-sterilized culture filtrates showed higher antibacterial activity than other treatments. A comparison of the antibacterial activity of culture filtrates and antibiotic streptomycin produced an inhibition zone of 18.5 mm and 15.5 mm respectively. This is the first report on the antibacterial activity of all the 3 bacterial strains (B. aryabhattai strain PR-D07, A. humicola strain PR-F07, and N. lactis strain PR-F11), against all the human pathogens, mentioned earlier. It is also found that the antibiotic factor is proteinaceous as proteinase K considerably reduced the antibacterial activity of the culture filtrates. With the above significant results, these 3 bacteria are considered to be promising candidates for the isolation of new antibacterial agents.

中文翻译：

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对人类致病菌具有抗菌活性的土壤细菌的分离、表征和分子鉴定

本研究涉及筛选来自印度班加罗尔不同地点的具有抗菌活性的土壤细菌。抗生素对细菌起到自卫机制的作用，并作为次级代谢产物产生以保护自己免受其他竞争性微生物的侵害。随着病原菌对用于治疗人类疾病的各种抗生素产生抗药性，对新抗生素的需求就出现了。鉴于细菌来源抗生素的重要性，标准技术已被用于分离和表征具有抗菌活性的土壤细菌。分离出的细菌通过一级和二级筛选方法对金黄色葡萄球菌、大肠杆菌、铜绿假单胞菌和肺炎克雷伯菌等人类致病菌进行了检测。分离株 PR1、PR2、两种方法均证实 PR3 和 PR3 对金黄色葡萄球菌、大肠杆菌、铜绿假单胞菌和肺炎克雷伯菌具有抗菌活性。对过滤灭菌、高压灭菌和蛋白酶 K 处理对培养物滤液的影响的研究表明，过滤灭菌是最好的方法。不同碳源和氮源对抗菌活性的影响表明，每个分离株对碳和氮需求的偏好不同。分离株PR1、PR2和PR3经16S rRNA测序鉴定为Bacillus aryabhattai菌株PR-D07、腐殖质节杆菌菌株PR-F07和乳酸新微球菌菌株PR-F11。这项研究工作的结果令人鼓舞，可以进一步推进应用方面。来自土壤样品的 263 株分离株中只有 3 株显示出对人类病原体金黄色葡萄球菌、大肠杆菌、铜绿假单胞菌和肺炎克雷伯菌的抗菌活性。它们通过 16S rRNA 研究被鉴定为 B. aryabhattai、A. humicola 和 N. lactis，并且它们都是革兰氏阳性的。每个分离株优选不同的碳源和氮源，因为它们增强了抗菌活性。这些分离物的培养滤液的功效通过过滤灭菌、高压灭菌和蛋白酶 K 处理进行测试。过滤灭菌的培养滤液显示出比其他处理更高的抗菌活性。比较培养物滤液和抗生素链霉素的抗菌活性，分别产生了 18.5 毫米和 15.5 毫米的抑菌圈。这是关于所有 3 种细菌菌株（B. aryabhattai PR-D07、A. humicola 菌株 PR-F07 和 N. lactis 菌株 PR-F11）对所有人类病原体的抗菌活性的首次报告，如前所述. 还发现抗生素因子是蛋白质的，因为蛋白酶 K 显着降低了培养物滤液的抗菌活性。有了上述显着结果，这 3 种细菌被认为是分离新型抗菌剂的有希望的候选者。