Hossain M Ismail, Saleh Nusrat U A, Numan Al, Hossain M Mahtab, Uddin M Aftab, Hossain Muktadir S
Department of Biochemistry and Microbiology, School of Health and Life Sciences, North South University, Dhaka, Bangladesh.
Bangladesh Sericulture Research and Training Institute, Rajshahi, Bangladesh.
Drug Discov Ther. 2023 Mar 11;17(1):18-25. doi: 10.5582/ddt.2022.01112. Epub 2023 Feb 27.
Increasing incidences of resistance to antibiotics by pathogenic bacteria is a worldwide concern and isolation of antibiotic-resistant strains of Niallia circulans (formerly known as Bacillus circulans), an opportunistic human pathogen, has been reported. Due to their lack of ethical constraints as well as their cost-effective rearing, invertebrates have been commonly used to study infection by bacteria pathogenic to humans. In this study, we demonstrate that a foodborne strain of N. circulans kills larvae of the silkworm, Bombyx mori within 48 h after hemolymph injection. The infected larvae turned black with an increase in the phenoloxidase (PO) activity in the hemolymph. Midgut injection of N. circulans resulted in the killing of larvae within 96 h. A significant increase in bacterial load was observed in the hemolymph 12 h after infection. The viable hemocyte number decreased to 48% within 12 h of injection. RT-qPCR analysis revealed that upon hemolymph infection with N. circulans the expression of the antimicrobial peptide (AMP) genes, Bmdefensin-B and Bmgloverin-3, were upregulated 2.5- and 1.8-fold, respectively, whereas 1.6-fold upregulation was observed for BmToll-2 in the larval fat body. Therapeutic effects of antibiotics like tetracycline, imipenem, ceftriaxone, ampicillin, and clindamycin were observed against N. circulans in the Bombyx larvae with varying efficacies. Results from this study suggest that larvae of B. mori can be used as infection models for screening therapeutics that are effective against N. circulans.
病原菌对抗生素的耐药性日益增加是一个全球性问题，据报道已分离出机会性人类病原体环状尼尔利亚菌（以前称为环状芽孢杆菌）的耐药菌株。由于无脊椎动物缺乏伦理限制且饲养成本效益高，它们通常被用于研究人类致病性细菌的感染。在本研究中，我们证明食源性环状尼尔利亚菌菌株在血淋巴注射后48小时内可杀死家蚕幼虫。受感染的幼虫变黑，血淋巴中的酚氧化酶（PO）活性增加。向中肠注射环状尼尔利亚菌导致幼虫在96小时内死亡。感染后12小时，血淋巴中的细菌载量显著增加。注射后12小时内，存活血细胞数量降至48%。RT-qPCR分析显示，血淋巴感染环状尼尔利亚菌后，抗菌肽（AMP）基因Bmdefensin-B和Bmgloverin-3的表达分别上调2.5倍和1.8倍，而幼虫脂肪体中的BmToll-2上调1.6倍。观察到四环素、亚胺培南、头孢曲松、氨苄西林和克林霉素等抗生素对家蚕幼虫中的环状尼尔利亚菌有不同疗效的治疗作用。本研究结果表明，家蚕幼虫可作为筛选对环状尼尔利亚菌有效的治疗药物的感染模型。
