Abstract:

Objective　To investigate the distribution of Francisella from near-shore shallow coastal areas in Guangdong, China by analyzing the seawater samples from various sources. Methods　Nineteen and 29 water samples were collected from the near-shore shallow coastal areas at Shuidong Bay at Dianbai District, Maoming City (on October 4, 2019) and Xunliao Bay and Double-Moon Bay in Huizhou City (on August 12, 2019) in Guangdong, China. The early exploratory outcomes of the optimal pretreatment method (concentrate and acid treatment) and culture medium (BHI-2216E-GVPC and BCYEα-2216E-GVPC) were applied to isolate Francisella. The colonies were selected based on Francisella colony morphology and the selected single colonies were cultured separately on plates to get the pure culture for further study, such as traditional morphological features, biochemical/physiological features, and 16S rRNA gene sequencing identification. Results　Fourteen of the 19 samples were positive (73.7%) and were collected from Shuidong Bay, and a total of 60 strains (including facultative intracellular bacteria) were isolated. Seventeen of the 29 samples were positive (58.6%), and were collected from Huizhou City, and a total of 79 strains (including facultative intracellular bacteria) were isolated. We examined the morphological, biochemical and 16S rRNA gene features of all the isolated strains. Among the 60 strains from Shuidong Bay, 12 strains (20.0%, including potential new species) were identified into Francisella, and 2 strains belonged to a potential new family (2.9%). Among the 79 strains from Huizhou City, 22 strains (27.8%, including potential new species) were identified into Francisella, and 18 strains (22.8%) belonged to a potential new family. Conclusion　The Francisella resources, including potential new species, and its neighboring potential new family are abundant in near-shore shallow coastal areas in Guangdong, China.

Key words: Francisella, Isolation and cultivation, Identification

摘要： 目的　对广东地区近海浅海海水弗朗西斯菌进行分离培养，以了解弗朗西斯菌在近海浅海海水中的分布情况。方法　在广东近海浅海地区水域内，选取茂名市电白区水东湾（2019年10月4日）以及惠州市两大湾（巽寮湾、双月湾，2019年8月12日）进行多点采集水样，分别19份和29份。利用前期探索出针对分离弗朗西斯菌的有效海水前处理手段（浓缩、酸处理）以及分离培养基（BHI-2216E-GVPC和BCYEα-2216E-GVPC）进行分离培养，依据弗朗西斯菌的菌落特征，初步将可疑菌株进行分纯培养，并对纯培养后的可疑菌株进行传统形态特征、生理生化特征、16S rRNA分子特征等鉴定。结果　19份水东湾水样中有14份（阳性率为73.7%）成功分离到共60株目标菌（含邻近兼性胞内寄生菌）；29份惠州地区水样中有17份（阳性率为58.6%）成功分离到共79株目标菌（含邻近兼性胞内寄生菌）。经菌落特征、细菌形态学检查、生化反应以及测序结果比对后，水东地区60株目标菌分离出弗朗西斯菌属（含潜在新种）12株（20.0%），潜在新科2株（2.9%），惠州地区79株目标菌分离出弗朗西斯菌属（含潜在新种）22株（27.8%），潜在新科18株（22.8%）。结论　广东地区近海浅海海水中弗朗西斯菌菌种资源丰富，且存在不同的该菌属内新种以及可能存在邻近新属。

关键词: 弗朗西斯菌, 分离培养, 鉴定