Genomic Characterization of a Streptococcus suis Serotype 2 Isolated from a Human Patient

Streptococcus suis(S. suis) is a Gram-positive zoonotic pathogen. S. suis infection in humans commonly causes meningitis, septicemia, arthritis,and streptococcal toxic shock-like syndrome(STSLS). S. suis has 29 serotypes, of which S. suis serotype 2(SS2) has the highest clinical isolation rate and strongest pathogenicity and causes most S. suis human infections.About 1,000 different sequence types(STs)were identified in S.suis based on multilocus sequence typing(MLST).Among these,STs,ST1,and ST7 belong to serotype 2 and are the major hazards of S.suis.in 1998 and 2005,two cases of SS2 human infection outbreak were reported in Jiangsu and Sichuan,China,causing 14 deaths and 38 deaths,respectively.

Identification of Antigens Common to Streptococcus suis Serotypes 2 and 9 by Immunoproteomic Analysis

Streptococcus suis is a Gram-positive pathogen that causes serious diseases in pigs. In addition to S. suis serotype 2 （SS2）, S. suis serotype 9 （SS9） is another prevalent serotype, which is frequently isolated from the organs of diseased pigs in China. An immunoproteomic-based approach was developed to identify antigens common to SS2 and SS9 for vaccine development. Cell wall proteins extracted from SS2 strain HA9801 were screened by two-dimensional Western blot using anti-SS2 sera, anti-SS9 sera, or pre-immune sera pooled from specific pathogen free （SPF） mice. Protein spots on preparative gels were excised and identified by matrix-assisted laser desorption ionization time-of-flight mass spectrometry, which led to the identification of four shared immunogenic proteins （arginine deiminase, translation elongation factor-Ts, o-acetylserine lyase, and 1-phosphofructokinase）. The genes encoding these four proteins from SS9 strain GZ0565 were cloned and their proteins were overexpressed in Escherichia coli BL21. Western blot analysis of these recombinant proteins using the convalescent serum of an SPF mini-pig inoculated with the SS2 strain, anti-SS2 sera, and anti-SS9 sera pooled from SPF mice further confirmed the immunogenicity of these proteins. These immunogenic proteins, which are encoded by genes that are reasonably conserved among SS2 and SS9 strains, could be developed as vaccine candidates.

Antibacterial activity evaluation of a novel K3-specific phage against Acinetobacter baumannii and evidence for receptor-binding domain transfer across morphologies

Acinetobacter baumannii(A.baumannii)poses a serious public health challenge due to its notorious antimicrobial resistance,particularly carbapenem-resistant A.baumannii(CRAB).In this study,we isolated a virulent phage,named P1068,from medical wastewater capable of lysing CRAB,primarily targeting the K3 capsule type.Basic characterization showed that P1068 infected the A.baumannii ZWAb014 with an optimal MOI of 1,experienced a latent period of 10 min and maintained stability over a temperature range of 4–37C and pH range of 3–10.Phylogenetic and average nucleotide identity analyses indicate that P1068 can be classified as a novel species within the genus Obolenskvirus of the Caudoviricetes class as per the most recent virus classification released by the International Committee on Taxonomy of Viruses(ICTV).Additionally,according to classical morphological classification,P1068 is identified as a T4-like phage(Myoviridae).Interestingly,we found that the tail fiber protein(TFP)of P1068 shares 74%coverage and 88.99%identity with the TFP of a T7-like phage(Podoviridae),AbKT21phiIII(NC_048142.1).This finding suggests that the TFP gene of phages may undergo horizontal transfer across different genera and morphologies.In vitro antimicrobial assays showed that P1068 exhibited antimicrobial activity against A.baumannii in both biofilm and planktonic states.In mouse models of intraperitoneal infection,P1068 phage protected mice from A.baumannii infection and significantly reduced bacterial loads in various tissues such as the brain,blood,lung,spleen,and liver compared to controls.In conclusion,this study demonstrates that phage P1068 might be a potential candidate for the treatment of carbapenem-resistant and biofilmforming A.baumannii infections,and expands the understanding of horizontal transfer of phage TFP genes.

Identification of a phage-derived depolymerase specific for KL47 capsule of Klebsiella pneumoniae and its therapeutic potential in mice

Klebsiella pneumoniae is one of the major pathogens causing global multidrug-resistant infections.Therefore,strategies for preventing and controlling the infections are urgently needed.Phage depolymerase,often found in the tail fiber protein or the tail spike protein,is reported to have antibiofilm activity.In this study,phage P560isolated from sewage showed specific for capsule locus type KL47 K.pneumoniae,and the enlarged haloes around plaques indicated that P560 encoded a depolymerase.The capsule depolymerase,ORF43,named P560dep,derived from phage P560 was expressed,purified,characterized and evaluated for enzymatic activity as well as specificity.We reported that the capsule depolymerase P560dep,can digest the capsule polysaccharides on the surface of KL47 type K.pneumoniae,and the depolymerization spectrum of P560dep matched to the host range of phage P560,KL47 K.pneumoniae.Crystal violet staining assay showed that P560dep was able to significantly inhibit biofilm formation.Further,a single dose(50μg/mouse)of depolymerase intraperitoneal injection protected 90%–100%of mice from lethal challenge before or after infection by KL47 carbapenem-resistant K.pneumoniae.And pathological changes were alleviated in lung and liver of mice infected by KL47 type K.pneumoniae.It is demonstrated that depolymerase P560dep as an attractive antivirulence agent represents a promising tool for antimicrobial therapy.