摘要
[Objectives]This study aimed to investigate the pathogenicity,growth characteristics and drug resistance of Streptococcus suis type 2.[Methods]Bacterial isolation and identification,biochemical experiments,determination of growth curve and correlation curve between OD 600 values and viable counts,drug susceptibility tests,pathogenicity analysis,and histopathological observations were carried out.[Results]The Streptococcus strain isolated from infected pigs was identified as Streptococcus suis type 2,which was named TA01 strain.TA01 strain reached the growth peak at 6-8 h post-incubation,and viable counts gradually declined after 8 h of incubation.The correlation equation between OD 600 values and viable counts is y=24.659 x-1.076 1,R^2=0.996 7.TA01 strain was sensitive to penicillin,erythromycin,florfenicol and oxacillin,and resistant to ciprofloxacin,polymyxin B and clindamycin.According to the results of pathogenicity analysis,all the mice in 3.6×10^9 cfu/mouse group died within 48,and these dead mice exhibited acute pyaemia septica.Based on the Reed-Muench formula,it was calculated that LD 50 of TA01 strain was 1.137×10^8 cfu/mouse.Pathological examination showed obvious blue-stained bacteria clusters,accompanied by neutrophil infiltration.[Conclusions]TA01 strain was a virulent strain of Streptococcus suis type 2.Compared with Streptococcus strains which were isolated and reported in China,TA01 strain exhibited strong virulence and rapid proliferation.
[Objectives] This study aimed to investigate the pathogenicity, growth characteristics and drug resistance of Streptococcus suis type 2. [Methods] Bacterial isolation and identification, biochemical experiments, determination of growth curve and correlation curve between OD600 values and viable counts, drug susceptibility tests, pathogenicity analysis, and histopathological observations were carried out. [Results] The Streptococcus strain isolated from infected pigs was identified as Streptococcus suis type 2, which was named TA01 strain. TA01 strain reached the growth peak at 6-8 h post-incubation, and viable counts gradually declined after 8 h of incubation. The correlation equation between OD600 values and viable counts is y=24.659x-1.076 1, R2=0.996 7. TA01 strain was sensitive to penicillin, erythromycin, florfenicol and oxacillin, and resistant to ciprofloxacin, polymyxin B and clindamycin. According to the results of pathogenicity analysis, all the mice in 3.6×109 cfu/mouse group died within 48, and these dead mice exhibited acute pyaemia septica. Based on the Reed-Muench formula, it was calculated that LD50 of TA01 strain was 1.137×108 cfu/mouse. Pathological examination showed obvious blue-stained bacteria clusters, accompanied by neutrophil infiltration. [Conclusions] TA01 strain was a virulent strain of Streptococcus suis type 2. Compared with Streptococcus strains which were isolated and reported in China, TA01 strain exhibited strong virulence and rapid proliferation.
基金
Supported by National Key Basic Research Program of China(973 Program)(2017YFD0500605)
