In the present study, 134 morphologically distinct actinobacteria isolates were obtained from soil samples from 10 different localities in the Saudi Arabian desert. The preliminary screening revealed that 16 of these isolates possessed antimicrobial activity. One isolate, which was identified as Streptomyces sp. DA3-7, possessed broad-spectrum antimicrobial activity against both gram-positive and gram-negative bacteria, as well as against fungi, and modified nutrient glucose medium was suitable for Streptomyces sp. DA3-7 to produce extracellular metabolites. The ethyl acetate extract of Streptomyces sp. DA3-7 exhibited antimicrobial activity against Enterococcus faecalis and Salmonella typhimurium, with minimum inhibitory concentrations of 78 and 156 μg/mL, respectively, as well as strong cytotoxicity (24 h IC₅₀ 85 μg/mL) against MCF-7 human breast adenocarcinoma cells. The active compound was separated, purified, and identified as Pyridine-2,5-diacetamide (C₉H₁₁N₃O₂ + H+, 194.21), which possessed a lowest minimum inhibitory concentration (31.25 μg/mL) against both Escherichia coli and Cryptococcus neoformans. The antimicrobial activities of this novel compound are reported here for the first time.

在本研究中，从沙特阿拉伯沙漠中10个不同地区的土壤样品中获得了134个形态上不同的放线菌分离株。初步筛选显示，其中的16株具有抗菌活性。一种分离物，被鉴定为链霉菌。DA3-7对革兰氏阳性和革兰氏阴性细菌以及真菌均具有广谱抗菌活性，改良的营养葡萄糖培养基适用于链霉菌。DA3-7产生细胞外代谢产物。链霉菌的乙酸乙酯提取物。DA3-7对粪肠球菌和鼠伤寒沙门氏菌具有抗菌活性分别对MCF-7人乳腺癌细胞具有最低抑制浓度，分别为78和156μg/ mL的最低抑制浓度以及较强的细胞毒性（24 h IC _50为85μg/ mL）。分离，纯化并鉴定出活性化合物为吡啶-2,5-二乙酰胺（C ₉ H ₁₁ N ₃ O ₂  + H +，194.21），其对两种大肠杆菌的最低抑菌浓度最低（31.25μg/ mL）和新型隐球菌。这种新化合物的抗菌活性首次在这里报道。