Na-Phatthalung Pinanong, Chusri Sasitorn, Suanyuk Naraid, Voravuthikunchai Supayang Piyawan
Department of Microbiology and Excellence Research Laboratory on Natural Products, Faculty of Science and Natural Product Research Center of Excellence, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.
Faculty of Traditional Thai Medicine, Prince of Songkla University, Hat Yai, Songkhla 90112, Thailand.
J Med Microbiol. 2017 Apr;66(4):430-439. doi: 10.1099/jmm.0.000453. Epub 2017 Apr 21.
Rhodomyrtustomentosa is a Thai medicinal plant that has been attracting attention for its remarkable antibacterial properties against Gram-positive pathogenic bacteria. The purpose of this study was to evaluate the antibacterial properties of R. tomentosa leaf extract against Streptococcus agalactiae and Streptococcus iniae isolated from infected tilapia.
The anti-streptococcal activity of R. tomentosa was determined using broth microdilution assays.
The extract demonstrated strong antibacterial activity against the fish pathogens, with minimum inhibitory concentrations (MICs) ranging from 7.8‒62.5 µg ml-1. It was found to possess a dose-dependent bacteriostatic effect on this organism. Scanning electron microscopy revealed irregular and long chains of swollen cells, as well as corkscrew shapes andincomplete separation of cell division of S. agalactiae cells following the treatment at sub-MIC. Moreover, S. agalactiae cells pre-treated with the extract became more sensitive to oxidative stress induced by H2O2 than the untreated cells. Based on the mortality of Nile tilapia after intraperitoneal infection of S. agalactiae at median lethal dose (LD50), the pre-treated cells caused a significant (P<0.01) reduction in mortality of S. agalactiae-infected Nile tilapia.
The results suggested that R. tomentosa could be further developed as a simple and effective agent for the treatment of streptococcosis in Nile tilapia.
桃金娘是一种泰国药用植物，因其对革兰氏阳性病原菌具有显著的抗菌特性而备受关注。本研究的目的是评估桃金娘叶提取物对从感染罗非鱼中分离出的无乳链球菌和海豚链球菌的抗菌特性。
采用肉汤微量稀释法测定桃金娘的抗链球菌活性。
提取物对鱼类病原菌表现出较强的抗菌活性，最低抑菌浓度（MICs）范围为7.8‒62.5 µg ml-1。发现其对该生物体具有剂量依赖性抑菌作用。扫描电子显微镜显示，在亚抑菌浓度处理后，无乳链球菌细胞出现不规则的长链肿胀细胞、螺旋形状以及细胞分裂不完全分离的情况。此外，用提取物预处理的无乳链球菌细胞比未处理的细胞对H2O2诱导的氧化应激更敏感。根据尼罗罗非鱼在腹腔注射无乳链球菌半数致死剂量（LD50）后的死亡率，预处理的细胞使感染无乳链球菌的尼罗罗非鱼死亡率显著降低（P<0.01）。
结果表明，桃金娘可进一步开发成为治疗尼罗罗非鱼链球菌病的一种简单有效的药物。
