Singh Aman Preet, Preet Simran, Rishi Praveen
Department of Microbiology, Basic Medical Sciences Block, Panjab University, Sector-14, Chandigarh 160014, India.
Department of Biophysics, Basic Medical Sciences Block, Panjab University, Sector-14, Chandigarh 160014, India.
J Antimicrob Chemother. 2014 Jul;69(7):1877-87. doi: 10.1093/jac/dku049. Epub 2014 Mar 14.
Multidrug resistance exhibited by Salmonella strains has proved to be a big hurdle in the development of an effective anti-Salmonella therapy. In this context, we had previously demonstrated strong synergism of nisin/ceftriaxone and nisin/cefotaxime combinations against Salmonella enterica serovar Typhimurium. However, the mechanism remained unexplored. The present study was therefore planned in order to evaluate the underlying mechanisms responsible for the synergistic effect of nisin in combination with these β-lactam antibiotics against serovar Typhimurium.
A membrane permeabilization assay along with pulse labelling studies were performed to confirm the ability of the combinations to permeabilize the bacterial membrane and to verify their effects on macromolecule synthesis. Additionally, analysis of peroxidative liver damage was performed and levels of nitric oxide, antioxidant enzymes, tumour necrosis factor-α and nuclear factor-κB were also measured.
1-N-phenylnapthylamine (NPN) uptake assay results confirmed a permeabilization-dependent mechanism, as NPN was taken up by treated cells in a time- and concentration-dependent manner, indicating that the combination influenced membrane permeability. Likewise, dose- and time-dependent inhibition of DNA, RNA and protein synthesis in the presence of both the combinations was observed. Interestingly, synergistic results inferred from in vivo assays confirmed the immuno-modulatory effects of the combinations in the treated mice.
Nisin/ceftriaxone and nisin/cefotaxime combinations exert their antibacterial activity against Salmonella by multiple modes of action that involve membrane permeabilization, inhibition of DNA, RNA and protein synthesis and direct immuno-modulatory activity.
已证明沙门氏菌菌株表现出的多重耐药性是有效抗沙门氏菌疗法开发中的一大障碍。在此背景下，我们之前已证明乳酸链球菌素/头孢曲松和乳酸链球菌素/头孢噻肟组合对肠炎沙门氏菌血清型鼠伤寒沙门氏菌具有强大的协同作用。然而，其作用机制仍未被探索。因此，本研究旨在评估乳酸链球菌素与这些β-内酰胺类抗生素联合使用对鼠伤寒沙门氏菌血清型产生协同作用的潜在机制。
进行了膜通透性测定以及脉冲标记研究，以确认组合使细菌膜通透的能力，并验证它们对大分子合成的影响。此外，还进行了过氧化肝损伤分析，并测量了一氧化氮、抗氧化酶、肿瘤坏死因子-α和核因子-κB的水平。
1-N-苯基萘胺（NPN）摄取试验结果证实了一种依赖通透性的机制，因为处理后的细胞以时间和浓度依赖的方式摄取NPN，表明该组合影响了膜通透性。同样，在两种组合存在的情况下，观察到对DNA、RNA和蛋白质合成的剂量和时间依赖性抑制。有趣的是，体内试验得出的协同结果证实了组合对受试小鼠的免疫调节作用。
乳酸链球菌素/头孢曲松和乳酸链球菌素/头孢噻肟组合通过多种作用方式对沙门氏菌发挥抗菌活性，这些作用方式包括膜通透、抑制DNA、RNA和蛋白质合成以及直接的免疫调节活性。
