渔业研究2025，Vol.47Issue(6)：732-747,16.DOI:10.14012/j.jfr.2025057
蛙源与鱼源无乳链球菌的遗传分化、基因分型、毒力谱、耐药性与致病性比较研究
Comparative studies on genetic differentiation,genotyping,virulence profiles,drug resistance and pathogenicity of Streptococcus agalactiae of frog and fish origin
摘要
Abstract
[Objective]This study aims to investigate the differences in biological characteristics,molecular typing,and pathogenicity to bullfrogs among Streptococcus agalactiae strains from different host sources,providing a theoretical basis for aquaculture disease prevention and control.[Methods]Five frog-derived strains(one from Pelophylax nigromaculatus,14#;four from Rana catesbeiana,19#,20#,24#,25#)and two Nile tilapia(Oreochromis niloticus)-derived strains(TW2018-78,TW2021-21)were selected.Species identification was conducted using 16S rRNA phylogenetic analysis and detection of the cfb gene.Further analyses included growth characteristics,capsular polysaccharide serotyping,multilocus sequence typing(MLST),virulence and antibiotic resistance gene profiling,and evaluation of pathogenicity to bullfrogs through experimental infection.[Results]All seven strains were identified as S.agalactiae.Phylogenetic analysis revealed that frog-and O.niloticus-derived strains belonged to distinct evolutionary lineages.The frog-derived strains were all of the Ⅰb-ST261 type,optimally grew at 28 ℃,and tested negative for both haemolysis and synergistic haemolysis(CAMP test).In contrast,the O.niloticus-derived strains were of the Ⅰa-ST7 type,grew well at 37 ℃,and tested positive for β-haemolysis and the CAMP test.Experimental infections showed that strain 25#(frog-de-rived)was highly pathogenic to bullfrogs,while O.niloticus-derived strains were non-pathogenic.Virulence gene profiling showed that frog-derived strains commonly carried cfb,hylB,and sip,with some also harboring bca,bibA and fbsB,but lacked cylE and scpB.O.niloticus-derived strains carried a broader spectrum of vir-ulence genes.Antibiotic resistance gene analysis revealed that frog-derived strains only carried ermA,while O.niloticus-derived strains carried multiple resistance genes including ermA,sul1,qnrS,and pbp2x,with observed inconsistencies between genotype and phenotype.[Conclusion]S.agalactiae strains from different hosts ex-hibit significant differences in genetic background,physiology,virulence profiles,antimicrobial resistance,and pathogenicity,indicating potential host adaptation.The results of the study provides a theoretical basis for tar-geted prevention and control strategies of S.agalactiae in aquaculture.关键词
无乳链球菌/系统发育/多位点序列分型(MLST)/荚膜多糖血清型/毒力基因/耐药性/致病性Key words
Streptococcus agalactiae/phylogeny/multilocus sequence typing(MLST)/capsular polysaccharide serotype/virulence genes/drug resistance/pathogenicity分类
农业科技引用本文复制引用
戴景辉,周丹,白林,阳涛..蛙源与鱼源无乳链球菌的遗传分化、基因分型、毒力谱、耐药性与致病性比较研究[J].渔业研究,2025,47(6):732-747,16.基金项目
四川省科技厅项目(2022YFN0012) （2022YFN0012）
农业农村部水产营养与智慧养殖重点实验室平台建设项目(2022-2025) （2022-2025）
