Characterization of a novel podoviridae-phage infecting Serratia marcescens isolated in China / 病毒学报

Serratia marcescens jn01 was employed as the host for the isolation of phages from environmental sewage. One strain of phage named SmPjn was purified by picking transparent plaque with 2mm diameter and clear edge on the double-layer agar repeatedly. Electron micrographs indicated that the phage head was icosahedral with head size and tail length of (58 +/- 2.16) x (55 +/- 0.47) nm and (7 +/- 1.25) nm, respectively. On the basis of the morphology, this phage belongs to the family Podoviridae. Host-range determination revealed that the phage was capable of infecting the other two isolates of S. marcescens, P25 and CMCC41002. The optimal multiplicity of infection was 1. A one-step growth curve of SmPjn indicated that the latent period and burst size were estimated at 50 min and 1,125 pfu/cell, respectively . Genomic DNA of SmPjn was above 27kb in size and could be digested by Hind Ill and EcoR I into 11 and 9 visible fragments after electrophoresis, respectively. A novel Podoviridae-phage infecting S. marcescens was firstly reported in China.

Study on molecular epidemiology of major pathogenic Streptococcus suis serotypes in middle part of Jiangsu province / 中华流行病学杂志

<p><b>OBJECTIVE</b>To determine the prevalence of Streptococcus suis and major pathogenic serotypes in middle part of Jiangsu province.</p><p><b>METHODS</b>Tonsillar specimens from 303 slaughtered pigs aged 6 to 8 months were investigated for the presence of Streptococcus suis and major pathogenic serotypes by polymerase chain reaction (PCR) method. Bacteriological examination compared with molecular genetics identification for three Streptococcus suis isolates were also done.</p><p><b>RESULTS</b>The overall carrier rate of Streptococcus suis was up to 88.0%, with the percentages of serotype 1(14), 2(1/2), 7 and 9 were 9.6%, 8.5%, 11.3% and 29.5% respectively in 2005. While in 2006, the prevalence of Streptococcus suis was 82.5%, with capsular types 1 (14), 2 (1/2), 7 and 9 were accounted for 17.6%, 2.4%, 25.8% and 20.0% of all the specimens. All the three isolates belonged to Streptococcus suis serotype 2,named 2a, 2f and 14e, which exhibiting the virulent phenotype cps2+/gdh+/mrp-/lepf-/sly-/fbps+/orf2+/89k-, cps2+/lgdh+/mrp-/epf-/sly-/fbps-/orf2-/89k- and cps2+/gdh+/mrp-/epf-/sly-/fbps/orf2-/ respectively. These isolates were all susceptible to amoxicillin, ampicillin, penicillin and resistant to amikacin and tetraycline. Clinical signs were not noted in BALB/c mice and rabbit.</p><p><b>CONCLUSION</b>Prevalence of the Streptococcus suis among the healthy herds in the areas was very high, with various capsule types of Streptococcus suis involved in the same herds, and the virulent phenotype of these 3 isolates were very different from those prevalent Streptococcus suis serotype 2 virulent isolates frequently discovered from the epidemic areas.</p>

Construction of RevS gene knock-out mutant of Streptococcus suis serotype 2 / 中华流行病学杂志

<p><b>OBJECTIVE</b>To construct a gene knock-out mutant of response regulator named RevS in Streptococcus suis serotype 2 virulent strain 05ZYH33, and to investigate the effects of its deletion on the biological characters of this pathogen and the pathogenesis to mice and piglets.</p><p><b>METHODS</b>Recombinant gene knock-out vector consisting of Spc(r) cassette was constructed and flanking was constructed consisting of Spc(r) cassette with flanking homology regions to the RevS genes while the isogenic RevS-deficient mutant was screened by allelic replacement. The effects of RevS deletion on the basic biological characters of 05ZYH33 including growth stability, colonial morphology, haemolysis, Gram staining, growth curve and protein expression were examined in vitro. The mice and piglets were infected with 10(8) CFU wild virulent and mutant isolates.</p><p><b>RESULTS</b>PCR analysis confirmed that the coding genes of RevS were replaced completely by Spc(r) cassette and the basic biological characters of 05ZYH33 did not undergo any apparent change. Balb/c mice infection assay indicated that RevS play a role in the pathogenesis of Streptococcus suis infections, while no remarkable difference was observed in the piglets' pathogenesis infection rates between mutant isolates deltaA05ZYH33 and wild-type isolates 05ZYH33.</p><p><b>CONCLUSION</b>The mutant of Streptococcus suis 05ZYH33 response regulator was successfully constructed, while the mutation did not obviously affect the bacterial biological characters, while the knock-out mutant of RevS was shown to be attenuated in pathogenesis to mice and piglets.</p>

Comparison of variable region genes of shrimp White Spot Syndrome Virus (WSSV) in different areas in China / 病毒学报

According to the conservative sequence in the epitaxial variable region of Thailand strain of WSSV published in GenBank,a pair of primers were designed to amplify the variable region genes of 5 local WSSV strains (ZHSH, ZHJ, HN, QD1, QD2) by PCR and then cloned. In accordance with the CN, the results indicated that the number of nucleotide of 5 strains were deleted more than 591bp of the TW and TH strains. The ZHSH and HN strains that deleted 591bp at the 3' end, and 454 bp at the 5' end of variable gene was highly homologous with CN strain about 99.3%. 229bp of ZHJ strain at the 5' end was homologous with CN about 99.3%, and deleted of 816bp at the 3' end. 97bp at the 5' end and 171bp at the 3' end of QD1 and QD2 strains were homologous with CN strain about 99.3%, and about 777bp were absent in the middle. The above data showed that the variable region genes of WSSV had mutated more in China. The variable region gene of QD2 strain was coincidence with that of QD1 after propagating 10 generations in crayfish. The results indicated that the crayfish inoculation did not result in mutation of variable region genes of WSSV.

Detection of virulence-associated factors of Streptococcus suis by multiplex PCR assay / 中华流行病学杂志

<p><b>OBJECTIVE</b>To rapidly and sensitively detect the four virulence-associated factors of Streptococcus suis, a multiplex PCR was developed.</p><p><b>METHODS</b>In the process of this reaction, four distinct DNA targets were amplified. One target was based on the serotype 2 (and 1/2) specific cps gene and the others were based on Streptococcus suis mrp, epf (epf*) and sly gene, encoding the MRP, EF(EF*) and Sly proteins of Streptococcus suis. 72 isolates, which including 48 strains of Streptococcus suis and 24 strains of negative control, and 49 clinical specimens were detected by the multiplex PCR assay.</p><p><b>RESULTS</b>All PCR products were detected by electrophoresis on 1.2% agarose gels. With the 48 Streptococcus suis strains, the positive detection rates of cps2+, mrp+, epf+, epf*+ and sly+ were 16/48, 14/48, 12/48, 3/48 and 26/48,respectively. The results were confirmed by bacteriological examination. There were no specific amplification products including 49 clinical specimens and 24 negative control strains.</p><p><b>CONCLUSION</b>The results demonstrated that multiplex PCR was a highly specific and sensitive diagnostic tool for the detection of virulence-associated factors of streptococcus suis.</p>

Dynamic Distribution of Shrimp White spot syndrome virus (WSSV) Qingdao Strain in Crawfishes by Dot Hybridization / 中国病毒学

A fragment sized 400bp of White spot syndrome virus（WS SV，formerly de signated NOSV），recovered from recombinant plasmid pAFD, was labeled with Digox igenin as a probe to detect dynamic distribution of WSSV within 120h and 72h in crawfishes（Cambarus proclarkii） inoculated WSSV by oral taking and injecti on r espectively. Stomach epithelium, intestine epithelium, heart, gill, haemolymph, muscle, hepatopancreas, hypoderm, connective tissue and ovary of infected crawfi shes were examined for WSSV. In both groups, WSSV was first detected in heamoly mph at 12h p.i. and then disappeared. Again it was detected at 96h p.i. only in oral infection group and maintained till 120h p.i., but it didn't appear at 72h p.i. in injection group. WSSV in heart, muscle was detected at 36h p.i. in oral infection group and 24h p.i. in injection group respectively, and then increased generally. In addition, WSSV in intestine epithelium, connective tissue, ovary of oral infection group and intestine epithelium, hypoderm, ovary of injection g roup could also be detected. In dead crawfishes after 120h and 72h p.i. in two groups, WSSV could be detected in all the examined tissues and it demonstrated t hat systemic infection occurred in the animales. The tissue containing more amo unts of WSSV was hypoderm in oral infection group, while intestine epithelium, g ill, hypoderm, ovary in injection infection group. It deduced that WSSV first a ppears in haemolymph and then goes into heart, muscle and other tissues and prol iferates in them. Once again, WSSV is released into heamolymph resulting in syst emic infection till crawfishes' death.

HEMOLYSIN EXAMINATION OF SWINE STREPTOCOCCAL ISOLATES / 微生物学通报

The hemolysin production of 19 strains of Streptococcus spp. isolated from pigs in the Jiangsu and Shanghai regions in recent years were examined. Eight isolates of Streptococcus suis type 2 from Jiangsu showed weak hemolysis on blood agar, but a stronger reaction in Todd-Hewitt broth(THB). The hemolysin belonged to the group of thiol-activated hemolysins. Nine strains of Streptoccus equi subsp. zooepidemicus showed strong hemolysis on blood agar and in THB containing 5% new-born calf serum, but no hemolysis in THB alone. This hemolysin was similar to streptolysin S(SLS). Another two isolates were atypical members of Lancefield group C Streptococcus and showed strong hemolysis on blood agar and in THB with 5% new-born calf serum, but the hemolysin was unlike either streptolysin O or SLS.