Genetic characterization of phenicol-resistant Escherichia coli and role of wild-type repressor/regulator gene (acrR) on phenicol resistance.

The genetic basis for phenicol resistance was examined in 38 phenicol-resistant clinical Escherichia coli isolates from poultry. Out of 62 isolates, 38 showed resistance for chloramphenicol and nine for florfenicol, respectively. Each strain also demonstrated resistance to a variety of other antibiotics. Molecular detection revealed that the incidence rates of the cat1, cat2, flo, flo-R, cmlA, and cmlB were 32, 29, 18, 13, 0, and 0%, respectively. Nineteen strains were tolerant to organic solvents. PCR amplification of the complete acrR (regulator/repressor) gene of five isolates revealed the amino acid changes in four isolates. DNA sequencing showed the non-synonymous mutations which change the amino acid, silent mutation, and nucleotide deletion in four isolates. MY09C10 showed neither deletion nor mutation in nucleotide. The AcrA protein of the AcrAB multidrug efflux pump was overexpressed in these strains. Complementation with a plasmid-borne wild-type acrR gene reduced the expression level of AcrA protein in the mutants and partially restored antibiotic susceptibility one- to fourfold. This study shows that mutations in acrR are an additional genetic basis for phenicol resistance.

Identification and characterization of a Streptococcus equi ssp. zooepidemicus immunogenic GroEL protein involved in biofilm formation.

Streptococcus equi ssp. zooepidemicus (S. equi spp. zooepidemicus) is an opportunistic pathogen that causes major economic losses in the swine industry in China and is also a threat for human health. Biofilm formation by this bacterium has been previously reported. In this study, we used an immunoproteomic approach to search for immunogenic proteins expressed by biofilm-grown S. equi spp. zooepidemicus. Seventeen immunoreactive proteins were found, of which nine common immunoreactive proteins were identified in planktonic and biofilm-grown bacteria. The immunogenicity and protective efficacy of the S. equi spp. zooepidemicus immunoreactive GroEL chaperone protein was further investigated in mice. The protein was expressed in vivo and elicited high antibody titers following S. equi spp. zooepidemicus infections of mice. An animal challenge experiment with S. equi spp. zooepidemicus showed that 75% of mice immunized with the GroEL protein were protected. Using in vitro biofilm inhibition assays, evidence was obtained that the chaperonin GroEL may represent a promising target for the prevention and treatment of persistent S. equi spp. zooepidemicus biofilm infections. In summary, our results suggest that the recombinant GroEL protein, which is involved in biofilm formation, may efficiently stimulate an immune response, which protects against S. equi spp. zooepidemicus infections. It may therefore be a candidate of interest to be included in vaccines against S. equi spp. zooepidemicus infections.

Development of real-time PCR assay for detection of porcine circovirus-like virus P1 in domestic pigs in China.

BACKGROUND: The porcine circovirus-like agent P1 is a newly discovered DNA virus with a single-stranded circular genome that is highly homologous to that of porcine circovirus type 2. P1 infection can cause symptoms resembling postweaning multisystemic wasting syndrome. This study aims to develop a rapid, sensitive and specific method to detect P1. RESULTS: A pair of primers was designed and used to amplify a 119 bp DNA fragment to generate a recombinant plasmid which was served as the standard. A SYBR I qPCR protocol was established using the P1 recombinant plasmid standard and the sensitivity, specificity and stability of this method was analyzed. The results demonstrate a strong correlation with P1 recombinant plasmid titers when virus DNA copy numbers fall in between 10(0) ~ 10(9) copies/µL. This method doesn't detect pseudo rabies, porcine parvovirus or porcine reproductive and respiratory syndrome virus; moreover it can distinguish porcine circovirus type 2 from P1 by melting temperature analysis. Coefficient of variation for each batch of reaction is less than 5%. The serum virus titers of P1 positive in this study were measured by this protocol to be 10(3) to 10(7) copies/mL. CONCLUSIONS: The established qPCR is sensitive, specific, and reliable, which could be a useful tool when applied to quantification of P1 in a variety of samples from infected pigs.

The effects of upaB deletion and the double/triple deletion of upaB, aatA, and aatB genes on pathogenicity of avian pathogenic Escherichia coli.

Autotransporters (ATs) are associated with pathogenesis of Avian Pathogenic Escherichia coli (APEC). The molecular characterization of APEC ATs can provide insights about their relevance to APEC pathogenesis. Here, we characterized a conventional autotransporter UpaB in APEC DE205B genome. The upaB existed in 41.9 % of 236 APEC isolates and was predominantly associated with ECOR B2 and D. Our studies showed that UpaB mediates the DE205B adhesion in DF-1 cells, and enhances autoaggregation and biofilm formation of fimbria-negative E. coli AAEC189 (MG1655Δfim) in vitro. Deletion of upaB of DE205B attenuates the virulence in duck model and early colonization in the duck lungs during APEC systemic infection. Furthermore, double and triple deletion of upaB, aatA, and aatB genes cumulatively attenuated DE205B adhesion in DF-1 cells, accompanying with decreased 50 % lethal dose (LD50) in duck model and the early colonization in the duck lungs. However, DE205BΔupaB/ΔaatA/ΔaatB might "compensate" the influence of gene deletion by upregulating the expression of fimbrial adhesin genes yqiL, yadN, and vacuolating autotransporter vat during early colonization of APEC. Finally, we demonstrated that vaccination with recombinant UpaB, AatA, and AatB proteins conferred protection against colisepticemia caused by DE205B infection in duck model.

Effect of Tran on virulence through regulating metabolism and stress tolerance of Streptococcus suis serotype 2.

Streptococcus suis (SS) is an important zoonotic pathogen causing a variety of life-threatening infections in pigs and humans. Tran, a novel transcriptional regulator which was identified to be an infection-related factor in S. suis serotype 2 using suppression subtractive hybridization (SSH), has been reported by our group. In this study, a tran deletion mutant was constructed to compare with the wild-type ZY05719 in some biological characteristics. It is suggested that longer chains and relatively slower growth could be observed in tran deletion mutants. In order to identify gene transcription profiles, microarray analysis was performed. It indicated that the inactivation of Tran led to 130 differentially expressed genes spread throughout the genome. Among these, 21 genes were upregulated, and 109 genes were downregulated. Most of the differentially expressed genes were involved in bacterial metabolism, such as the phosphotransferase system (PTS), and heat shock proteins. In the case of glucose scarcity, the growth characteristics of tran deletion mutants were impacted significantly, meanwhile Δtran mutant was highly sensitive to environmental stresses. Moreover, cell adherence decreased by 22.2%, and virulence in zebrafish declined to more than five times in Δtran mutants. These data demonstrate the role of Tran in regulation in S. suis serotype 2, that is affect bacterial virulence by influencing bacterial metabolism and stress tolerance of external environment.

Biofilm formation of Streptococcus equi ssp. zooepidemicus and comparative proteomic analysis of biofilm and planktonic cells.

Streptococcus equi ssp. zooepidemicus (SEZ) is responsible for a wide variety of infections in many species, including pigs, horses and humans. Biofilm formation is essential for pathogenesis, and the ability to resist antibiotic treatment results in difficult-to-treat and persistent infections. However, the ability of SEZ to form biofilms is unclear. Furthermore, the mechanisms underlying SEZ biofilm formation and their attributes are poorly understood. In this study, scanning electron microscopy (SEM) demonstrated that SEZ strain ATCC35246 formed biofilms comprising a thick, heterogeneous layer with clumps on the coverslips when incubated for 24 h. In addition, we used a two-dimensional gel electrophoresis (2-DE) based approach to characterize differentially expressed protein in SEZ biofilms compared with their planktonic counterparts. The results revealed the existence of 24 protein spots of varying intensities, 13 of which were upregulated and 11 were downregulated in the SEZ biofilm compared with the planktonic controls. Most of proteins expressed during biofilm formation were associated with metabolism, adhesion, and stress conditions. These observations contribute to our understanding of the SEZ biofilm lifestyle, which may lead to more effective measures to control persistent SEZ infections.

A novel vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection.

To develop a vaccine against Porcine circovirus type 2 (PCV2) and Streptococcus equi ssp. zooepidemicus (SEZ) co-infection, the genes of porcine IL-18, capsid protein (Cap) of PCV2 and M-like protein (SzP) of SEZ were inserted into the swinepox virus (SPV) genome by homologous recombination. The recombinant swinepox virus rSPV-ICS was verified by PCR and indirect immunofluorescence assays. To evaluate the immunogenicity of rSPV-ICS, 28 PCV2 and SEZ seronegative Bama minipigs were immunized with rSPV-ICS (n=8), commercial PCV2 vaccine and SEZ vaccine (n=8) or wild type SPV (n=8). The results showed that SzP-specific antibody and PCV2 neutralizing antibody of the rSPV-ICS immunized group increased significantly compared to the wild type SPV treated group after vaccination and increased continuously over time. The levels of IL-4 and IFN-γ in the rSPV-ICS immunized group were significantly higher than the other three groups, respectively. After been co-challenged with PCV2 and SEZ, 87.5% piglets in rSPV-ICS immunized group were survived. Significant reductions in gross lung lesion score, histopathological lung lesion score, and lymph node lesion score were noticed in the rSPV-ICS immunized group compared with the wtSPV treated group. The results suggested that the recombinant rSPV-ICS provided piglets with significant protection against PCV2-SEZ co-infection; thus, it offers proof-of-principle for the development of a vaccine for the prevention of these swine diseases.

Identification of genes preferentially expressed by highly virulent piscine Streptococcus agalactiae upon interaction with macrophages.

Streptococcus agalactiae, long recognized as a mammalian pathogen, is an emerging concern with regard to fish. In this study, we used a mouse model and in vitro cell infection to evaluate the pathogenetic characteristics of S. agalactiae GD201008-001, isolated from tilapia in China. This bacterium was found to be highly virulent and capable of inducing brain damage by migrating into the brain by crossing the blood-brain barrier (BBB). The phagocytosis assays indicated that this bacterium could be internalized by murine macrophages and survive intracellularly for more than 24 h, inducing injury to macrophages. Further, selective capture of transcribed sequences (SCOTS) was used to investigate microbial gene expression associated with intracellular survival. This positive cDNA selection technique identified 60 distinct genes that could be characterized into 6 functional categories. More than 50% of the differentially expressed genes were involved in metabolic adaptation. Some genes have previously been described as associated with virulence in other bacteria, and four showed no significant similarities to any other previously described genes. This study constitutes the first step in further gene expression analyses that will lead to a better understanding of the molecular mechanisms used by S. agalactiae to survive in macrophages and to cross the BBB.

Identification and characterization of a novel hemolysis-related gene in Streptococcus suis serotype 2.

Streptococcussuis serotype 2 (SS 2) is an important zoonotic pathogen that has caused two major infectious outbreaks of streptococcal toxic shock syndrome (STSS) in China. A novel gene located in the 89K pathogenicity island (PAI) encoding a putative hemolysin-III-related protein (Hhly3) has been previously characterized. In this study, the SS2 deletion mutant of the exogenous gene hhly3 was constructed by homologous recombination. This protein was found to exhibit cytolytic activity, and hemolytic activity of the hhly3 gene knockout mutant (Δhhly3) was significantly lower than that in the wild-type strain ZY05719. In addition, qRT-PCR revealed that Hhly3 played an important role in the expression of the secreted hemolysin SLY, which may be the key reason for the decreased hemolytic activity. Consequently, compared with the WT strain, the infection and pathogenicity of Δhhly3 was also decreased, as evidenced by in vitro bacterial growth in whole blood and by the in vivo zebrafish test, suggesting that hhly3 is a novel exogenous hemolysis-related gene in SS2 strains.

Contribution of fibronectin-binding protein to pathogenesis of Streptococcus equi ssp. zooepidemicus.

Streptococcus equi ssp. zooepidemicus (S. zooepidemicus) is responsible for a wide variety of infections in many species. Fibronectin-binding protein is a bacterial cell surface protein, which specifically binds fibronectin (FN). Considering the specific role of FN-binding protein in host-pathogen interactions, we investigated the function of a novel FN-binding domain in the FN-binding protein (FNZ) of S. zooepidemicus. Five recombinant FNZ gene fragments [N1 (amino acids, 38-197), N2 (amino acids, 38-603), N3 (amino acids, 41-315), N4 (amino acids, 192-370), and N5 (amino acids, 38-225)] were expressed in Escherichia coli, and their FN-binding activities were tested. The results showed that amino acids 192-225 in the NH2 -terminal region of FNZ could be responsible for binding fibronectin. The FNZ knockout mutant was constructed in S. zooepidemicus, which results in the reduced capacity to adhere to HEp-2 cell, defective virulence in vivo, decreased biofilm formation, and decreased colonization capacity in blood, liver, lung, and spleen tissues of mice as compared to the wild type. These results suggest that FNZ participates in biofilm formation, FN binding, cell adhesion, and pathogenesis of S. zooepidemicus. Furthermore, this work offers a novel FN-binding domain within FNZ, which will help in further characterization of S. zooepidemicus FN-binding properties.

Tetrahymena: an alternative model host for evaluating virulence of Aeromonas strains.

An easier assessment model would be helpful for high-throughput screening of Aeromonas virulence. The previous study indicated the potential of Tetrahymena as a permissive model to examine virulence of Aeromonas hydrophila. Here our aim was to assess virulence of Aeromonas spp. using two model hosts, a zebrafish assay and Tetrahymena-Aeromonas co-culture, and to examine whether data from the Tetrahymena thermophila model reflects infections in the well-established animal model. First, virulence of 39 Aeromonas strains was assessed by determining the 50% lethal dose (LD(50)) in zebrafish. LD(50) values ranging from 1.3×10(2) to 3.0×10(7) indicated that these strains represent a high to moderate degree of virulence and could be useful to assess virulence in the Tetrahymena model. In Tetrahymena-Aeromonas co-culture, we evaluated the virulence of Aeromonas by detecting relative survival of Aeromonas and Tetrahymena. An Aeromonas isolate was considered virulent when its relative survival was greater than 60%, while the Aeromonas isolate was considered avirulent if its relative survival was below 40%. When relative survival of T. thermophila was lower than 40% after co-culture with an Aeromonas isolate, the bacterial strain was regarded as virulent. In contrast, the strain was classified as avirulent if relative survival of T. thermophila was greater than 50%. Encouragingly, data from the 39 Aeromonas strains showed good correlation in zebrafish and Tetrahymena-Aeromonas co-culture models. The results provide sufficient data to demonstrate that Tetrahymena can be a comparable alternative to zebrafish for determining the virulence of Aeromonas isolates.

Complete genome sequence of an H3N2 canine influenza virus from dogs in Jiangsu, China.

A canine influenza virus (CIV) strain of avian origin designated A/Canine/Jiangsu/06/2010 (H3N2) was isolated from dogs exhibiting severe respiratory disease in Jiangsu, China. We announce the complete genome sequence of this viral strain and report major findings from the genomic analysis. This sequence will help us understand the molecular characteristics and evolutionary of H3N2 CIV in China.

[Characterization of a novel podoviridae-phage infecting Serratia marcescens isolated in China].

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.

Complete Genome Sequence of Aeromonas hydrophila Phage CC2.

Aeromonas hydrophila is one of the major pathogenic bacteria for fish and people. To develop an effective antimicrobial agent, we isolated a bacteriophage from sewage, named CC2, and sequenced its genome. Comparative genome analysis of phage CC2 with its relatives revealed that phage CC2 has higher sequence homology to A. salmonicida phage 65 than to A. hydrophila phage Aeh1. Here, we announce the complete genome sequence of CC2 and report major findings from the genomic analysis.

Development of an Aeromonas hydrophila recombinant extracellular protease vaccine.

Aeromonas hydrophila (Ah) exists widely in the aquatic environment and infects a variety of animals. Extracellular protease (EPR) is an important protective antigen that induces a specific antibody response to resist Ah infection. In this study, two genes encoding extracellular protease epr2 and epr3 were linked within the expression vector pET32a to construct a recombinant pET-epr2-3 plasmid. The immunogenicity of the fusion protein epr2-3 was investigated as a subunit vaccine in ICR mice. The recombinant epr2-3 protein induced the production of high antibody titers. The survival rate against homogenous Ah J-1 challenge was significantly higher in the epr2-3 vaccinated group (≥80%) compared with the inactivated Ah vaccinated group and the challenge control group (P < 0.01), thus indicating that the recombinant epr2-3 protein provided significant protection against Ah infection. Therefore, the recombinant epr2-3 is a promising candidate for development as a vaccine against Ah infections.

Construction and immunogenicity of recombinant swinepox virus expressing capsid protein of PCV2.

To explore development of a vaccine against PCV2 infections, the gene of capsid protein (Cap) was inserted into the swinepox virus (SPV) genome by homologous recombination. The recombinant swinepox virus expressing capsid protein (rSPV-cap) was verified by PCR, western blot and immunofluorescence assays. To evaluate the immunogenicity of rSPV-cap, twenty-four PCV2 seronegative minipigs were immunized with rSPV-cap, wild type SPV (wtSPV; negative control), or PBS (challenge control). After inoculation with PCV2, pigs in the rSPV-cap immunized group showed significantly higher average daily weight gain (ADG) and shorter fever duration compared with the wtSPV treated group (P<0.05). Cap-specific antibody in the rSPV-cap immunized group increased dramatically after vaccination and increased continuously over time. PCV2 genomic copies in the serum of rSPV-cap immunized pigs were significantly less compared with the wtSPV treated group at all time points after inoculation (P<0.01). Significant reduction in gross lung lesion scores, histopathological lung lesion scores, and lymph node lesion scores were noted in the rSPV-cap immunized group compared with the wtSPV treated group (P<0.01). The results suggested that the recombinant rSPV-cap provided pigs with significant protection from PCV2-associated disease; thus, it offers proof-of-principle for the development of a vaccine for the prevention of PCV2-associated disease in pigs.

Virus-like particles of hepatitis B virus core protein containing five mimotopes of infectious bursal disease virus (IBDV) protect chickens against IBDV.

Current infectious bursal disease virus (IBDV) vaccines suffer from maternal antibody interference and mimotope vaccines might be an alternative. Previously we demonstrated an IBDV VP2 five-mimotope polypeptide, 5EPIS, elicited protective immunity in chickens. In the current study, the 5epis gene was inserted into a plasmid carrying human hepatitis B virus core protein (HBc) gene at its major immunodominant region site. The recombinant gene was efficiently expressed in Escherichia coli to produce chimeric protein HBc-5EPIS which self-assembles to virus-like particles (VLP). Two-week old specific-pathogen-free chickens were immunized intramuscularly with HBc-5EPIS VLP or 5EPIS polypeptide without adjuvant (50 µg/injection) on day 0, 7, 14 and 21. Anti-5EPIS antibody was first detected on day 7 and day 21 in HBc-5EPIS and 5EPIS groups, respectively; on day 28, anti-5EPIS titers reached 12,800 or 1600 by ELISA, and 3200 or 800 by virus neutralization assay in HBc-5EPIS and 5EPIS groups, respectively. No anti-5EPIS antibody was detected in the buffer control group throughout the experiment. Challenge on day 28 with a virulent IBDV strain (GX8/99) resulted in 100%, 40.0% and 26.7% survival for chickens immunized with HBc-5EPIS, 5EPIS and buffer, respectively. These data suggest epitope presentation on chimeric VLP is a promising approach for improving mimotope vaccines for IBDV.

Characterization and functional analysis of atl, a novel gene encoding autolysin in Streptococcus suis.

Streptococcus suis serotype 2 (S. suis 2) is an important swine and human pathogen responsible for septicemia and meningitis. A novel gene, designated atl and encoding a major autolysin of S. suis 2 virulent strain HA9801, was identified and characterized in this study. The Atl protein contains 1,025 amino acids with a predicted molecular mass of 113 kDa and has a conserved N-acetylmuramoyl-l-alanine amidase domain. Recombinant Atl was expressed in Escherichia coli, and its bacteriolytic and fibronectin-binding activities were confirmed by zymography and Western affinity blotting. Two bacteriolytic bands were shown in the sodium dodecyl sulfate extracts of HA9801, while both were absent from the atl inactivated mutant. Cell chains of the mutant strain became longer than that of the parental strain. In the autolysis assay, HA9801 decreased to 20% of the initial optical density (OD) value, while the mutant strain had almost no autolytic activity. The biofilm capacity of the atl mutant was reduced ∼30% compared to the parental strain. In the zebrafish infection model, the 50% lethal dose of the mutant strain was increased up to 5-fold. Furthermore, the adherence to HEp-2 cells of the atl mutant was 50% less than that of the parental strain. Based on the functional analysis of the recombinant Atl and observed effects of atl inactivation on HA9801, we conclude that Atl is a major autolysin of HA9801. It takes part in cell autolysis, separation of daughter cells, biofilm formation, fibronectin-binding activity, cell adhesion, and pathogenesis of HA9801.

Complete genome sequence of Streptococcus equi subsp. zooepidemicus strain ATCC 35246.

Streptococcus equi subsp. zooepidemicus is an opportunistic pathogen. It has caused a very large economic loss in the swine industry of China and has become a threat to human health. We announce the complete genome sequence of S. equi subsp. zooepidemicus strain ATCC 35246, which provides opportunities to understand its pathogenesis mechanism and genetic basis.

A novel vaccine against Streptococcus equi ssp. zooepidemicus infections: the recombinant swinepox virus expressing M-like protein.

To develop a safer, more immunogenic and efficacious vaccine against Streptococcus equi ssp. zooepidemicus (SEZ) infections, the gene of M-like protein (SzP) was placed under the strong vaccinia virus promoter P28 and then inserted into swinepox virus (SPV) genome. The recombinant swinepox virus (rSPV-szp) was isolated in a non-selective medium by the co-expression of Escherichia coli LacZ gene and verified by PCR, western blotting and immunofluorescence assays. To evaluate the immunogenicity of this rSPV-szp, ICR mice were immunized with the rSPV-szp, inactivated SEZ vaccine (positive control), wild type SPV (negative control), or PBS (challenge control). All mice were intraperitoneally challenged with 5 LD(50) of homogenous ATCC 35246 strain 14 days post-vaccination. The results showed that at least 70% mice in rSPV-szp-vaccinated group were protected against homogenous ATCC 35246 challenge, the survival rate was significantly higher compared with mice in the negative control group and the challenge control group (P<0.001). The antibody titers of the rSPV-szp-vaccinated group were significantly higher (P<0.05) than the other three groups. Passive immune protection assays showed that the hyperimmune sera against M-like protein could provide mice with complete protection against challenge of ATCC 35246. Semi-quantitative RT-PCR analysis showed a marked increased in levels of IL-4 and IFN-γ mRNA in immunized mice. The results suggested that the recombinant rSPV-szp provided mice with significant protection from the SEZ infections. It is a promising candidate for the vaccine development against SEZ infections.