Reduced virulence is an important characteristic of biofilm infection of Streptococcus suis

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.

Sub-MIC Tylosin Inhibits Streptococcus suis Biofilm Formation and Results in Differential Protein Expression

Streptococcus suis (S.suis) is an important zoonotic pathogen that causes severe diseases in humans and pigs. Biofilms of S. suis can induce persistent infections that are difficult to treat. In this study, the effect of tylosin on biofilm formation of S. suis was investigated. 1/2 minimal inhibitory concentration (MIC) and 1/4 MIC of tylosin were shown to inhibit S. suis biofilm formation in vitro. By using the iTRAQ strategy, we compared the protein expression profiles of S. suis grown with sub-MIC tylosin treatment and with no treatment. A total of 1501 proteins were identified by iTRAQ. Ninety-six differentially expressed proteins were identified (Ratio > ±1.5, p < 0.05). Several metabolism proteins (such as phosphoglycerate kinase) and surface proteins (such as ABC transporter proteins) were found to be involved in biofilm formation. Our results indicated that S. suis metabolic regulation, cell surface proteins, and virulence proteins appear to be of importance in biofilm growth with sub-MIC tylosin treatment. Thus, our data revealed the rough regulation of biofilm formation that may provide a foundation for future research into mechanisms and targets.

Characterization of avian pathogenic Escherichia coli isolated in eastern China

In order to investigate the biological characteristics of avian pathogenic Escherichia coli (APEC) isolated in eastern China, a total of 243 isolates were isolated from diseased poultry on different farms during the period from 2007 to 2014. These isolates were characterized for serogroups (polymerase chain reaction and agglutination), the presence of virulence-associated genes (fimC, iss, ompA, fyuA, stx2f, iroC, iucD, hlyE, tsh, cvaC, irp2, and papC) and class I integrons (polymerase chain reaction), drug susceptibilities (disk diffusion method) and the biofilm-forming abilities (semi-quantitative method). The results showed that the most predominant serogroups were O78 (87 isolates, 35.8%) and O2 (35 isolates, 14.4%). Gene profiling found that fimC and ompA were frequently distributed among the isolates and that 77.4% of the isolates were positive for class 1 integrons. Overall, isolates displayed resistance to tetracycline (97.5%), nalidixic acid (82.3%), ampicillin (81.1%), sulphafurazole (80.7%), streptomycin (79.0%), trimethoprim (78.2%) and cotrimoxazole (78.2%). Multiple-drug resistance was exhibited in 80.3% of the isolates, and the presence of class 1 integrons is associated with multidrug resistance. Finally, 151 isolates had the ability to form biofilms in vitro, and drug resistance seemed relative to biofilm-forming abilities.

Quantitative proteomic analysis of sub-MIC erythromycin inhibiting biofilm formation of S. suis in vitro

Streptococcus suis (S. suis) is a swine pathogen and also a zoonotic agent. Biofilms of S. suis may cause persistent infections by the host immune system and antibiotics. Sub-minimal inhibitory concentration (sub-MIC) of erythromycin can inhibit biofilm formation in bacteria. Here, we performed comparative proteomic analyses of cells at two different conditions: sub-MIC erythromycin treated and nontreated cells. Using iTRAQ strategy, we found some novel proteins that involved in biofilm formation. 79 differentially expressed proteins were identified in sub-MIC erythromycin inhibiting planktonic cell when the protein had both a fold-change of more that a ratio >1.2 or <0.8 (p-value <0.05). Several cell surface proteins (such as Primosomal protein N', l-fucose isomerase, and ABC superfamily ATP binding cassette transporter, membrane protein), as well as those involved in Quorum-sensing, were found to be implicated in biofilm formation. Overall, our results indicated that cell surface proteins played an important role in biofilm formation. Quorum-sensing played a crucial role leading to biofilm formation. ABC superfamily ATP binding cassette transporter, membrane protein and comD might act as channels for erythromycin uptake in Quorum-sensing system. Thus, our data analyzed rough regulatory pathways of biofilm formation that might potentially be exploited to deal with biofilm infections of S. suis. This article is part of a Special Issue entitled: Microbial Proteomics.

BIOLOGICAL SIGNIFICANCE

In this study, we identified many proteins involved in cell transport, biological regulation and signal transduction, stress responses and other metabolic processes that were not previously known to be associated with biofilm formation of S. suis and target spot of erythromycin. Therefore, our manuscript represents the most comprehensive analysis of protein profiles of biofilm formation of S. suis inhibited by sub-MIC erythromycin and provides new proteomic information about biofilm formation.

Functional analysis of c-di-AMP phosphodiesterase, GdpP, in Streptococcus suis serotype 2

Streptococcus suis serotype 2 (SS2) is an important zoonotic pathogen that causes serious diseases in pigs and humans. GdpP protein is a recently discovered specific phosphodiesterase that degrades cyclic diadenosine monophosphate (c-di-AMP). It is widely distributed among the firmicutes phylum and altered expression of GdpP is associated with several phenotypes in various bacterial strains. We investigated the role of GdpP in physiology and virulence in SS2. An in-frame mutant of gdpP was constructed using homologous recombination and bacterial growth, biofilm formation, hemolytic activity, cell adherence and invasion, expression of virulence factors, and virulence were evaluated. Disruption of gdpP increased intracellular c-di-AMP level and affected growth and increased biofilm formation of SS2. Simultaneously, the gdpP mutant strain exhibited a significant decrease in hemolytic activity and adherence to and invasion of HEp-2 cells compared with the parental strain. Quantitative reverse transcriptase polymerase chain reaction indicated significantly reduced expression of the known virulence genes cps2, sly, fpbs, mrp, ef and gdh in the gdpP mutant. In murine infection models, the gdpP mutant strain was attenuated, and impaired bacterial growth was observed in specific organs. All these findings revealed a significant contribution of gdpP and its substrate (c-di-AMP) to the biology and virulence of SS2.

Biofilm formation, host-cell adherence, and virulence genes regulation of Streptococcus suis in response to autoinducer-2 signaling

Autoinducer-2 (AI-2) is a universal signal molecule mediating intra- and interspecies communication among bacteria. AI-2 is a byproduct of the LuxS enzyme during the catabolism of S-adenosylhomocysteine and plays critical roles in regulating various behaviors of bacteria. In our previous study, the function of LuxS in AI-2 production was verified in Streptococcus suis (SS). Decreased levels of SS biofilm formation and host-cell adherence as well as the inability to produce AI-2 were observed in SS having a luxS mutant gene. In this study, exogenous addition of a low concentration of AI-2 synthesized in vitro was found to promote biofilm formation and host-cell adherence. However, higher concentrations of AI-2 inhibited SS biofilm formation and host-cell adherence. Real-time PCR results showed that the mRNA level of virulence factors of SS biofilm, gdh, cps2, sly, and mrp increased and ef, fbps, and gapdh decreased with increasing AI-2 concentrations. These findings demonstrated that AI-2 supplemented exogenously acted as a concentration-dependent signaling molecule to regulate SS biofilm formation, host-cell adherence, and transcription levels of many virulence genes.

Comparative genomic analysis shows that Streptococcus suis meningitis isolate SC070731 contains a unique 105K genomic island

Streptococcus suis (SS) is an important swine pathogen worldwide that occasionally causes serious infections in humans. SS infection may result in meningitis in pigs and humans. The pathogenic mechanisms of SS are poorly understood. Here, we provide the complete genome sequence of S. suis serotype 2 (SS2) strain SC070731 isolated from a pig with meningitis. The chromosome is 2,138,568bp in length. There are 1933 predicted protein coding sequences and 96.7% (57/59) of the known virulence-associated genes are present in the genome. Strain SC070731 showed similar virulence with SS2 virulent strains HA9801 and ZY05719, but was more virulent than SS2 virulent strain P1/7 in the zebrafish infection model. Comparative genomic analysis revealed a unique 105K genomic island in strain SC070731 that is absent in seven other sequenced SS2 strains. Further analysis of the 105K genomic island indicated that it contained a complete nisin locus similar to the nisin U locus in S. uberis strain 42, a prophage similar to S. oralis phage PH10 and several antibiotic resistance genes. Several proteins in the 105K genomic island, including nisin and RelBE toxin-antitoxin system, contribute to the bacterial fitness and virulence in other pathogenic bacteria. Further investigation of newly identified gene products, including four putative new virulence-associated surface proteins, will improve our understanding of SS pathogenesis.

Overexpression of luxS cannot increase autoinducer-2 production, only affect the growth and biofilm formation in Streptococcus suis

LuxS/AI-2 quorum sensing (QS) system involves the production of cell signaling molecules via luxS-based autoinducer-2 (AI-2). LuxS has been reported to plays critical roles in regulating various behaviors of bacteria. AI-2 is a byproduct of the catabolism of S-adenosylhomocysteine (SAH) performed by the LuxS and Pfs enzymes. In our previous study, the function of LuxS in AI-2 production was verified in Streptococcus suis (SS). Decreased levels of SS biofilm formation and host-cell adherence as well as an inability to produce AI-2 were observed in bacteria having a luxS mutant gene. In this study, the level of AI-2 activity exhibits a growth-phase dependence with a maximum in late exponential culture in SS. An SS strain that overexpressed luxS was constructed to comprehensively understand the function of AI-2. Overexpressed luxS was not able to increase the level of pfs expression and produce additional AI-2, and the bacteria were slower growing and produced only slightly more biofilm than the wild type. Thus, AI-2 production is not correlated with luxS transcription. luxS expression is constitutive, but the transcription of pfs is perhaps correlated with AI-2 production in SS.

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.

Virulence factors involved in the pathogenesis of the infection caused by the swine pathogen and zoonotic agent Streptococcus suis

Streptococcus suis is a major swine pathogen responsible for important economic losses to the swine industry worldwide. It is also an emerging zoonotic agent of meningitis and streptococcal toxic shock-like syndrome. Since the recent recognition of the high prevalence of S. suis human disease in southeast and east Asia, the interest of the scientific community in this pathogen has significantly increased. In the last few years, as a direct consequence of these intensified research efforts, large amounts of data on putative virulence factors have appeared in the literature. Although the presence of some proposed virulence factors does not necessarily define a S. suis strain as being virulent, several cell-associated or secreted factors are clearly important for the pathogenesis of the S. suis infection. In order to cause disease, S. suis must colonize the host, breach epithelial barriers, reach and survive in the bloodstream, invade different organs, and cause exaggerated inflammation. In this review, we discuss the potential contribution of different described S. suis virulence factors at each step of the pathogenesis of the infection. Finally, we briefly discuss other described virulence factors, virulence factor candidates and virulence markers for which a precise role at specific steps of the pathogenesis of the S. suis infection has not yet been clearly established.

Comparative proteomic analysis of Streptococcus suis biofilms and planktonic cells that identified biofilm infection-related immunogenic proteins

Streptococcus suis (SS) is a zoonotic pathogen that causes severe disease symptoms in pigs and humans. Biofilms of SS bind to extracellular matrix proteins in both endothelial and epithelial cells and cause persistent infections. In this study, the differences in the protein expression profiles of SS grown either as planktonic cells or biofilms were identified using comparative proteomic analysis. The results revealed the existence of 13 proteins of varying amounts, among which six were upregulated and seven were downregulated in the Streptococcus biofilm compared with the planktonic controls. The convalescent serum from mini-pig, challenged with SS, was applied in a Western blot assay to visualize all proteins from the biofilm that were grown in vitro and separated by two-dimensional gel electrophoresis. A total of 10 immunoreactive protein spots corresponding to nine unique proteins were identified by MALDI-TOF/TOF-MS. Of these nine proteins, five (Manganese-dependent superoxide dismutase, UDP-N-acetylglucosamine 1-carboxyvinyltransferase, ornithine carbamoyltransferase, phosphoglycerate kinase, Hypothetical protein SSU05_0403) had no previously reported immunogenic properties in SS to our knowledge. The remaining four immunogenic proteins (glyceraldehyde-3-phosphate dehydrogenase, hemolysin, pyruvate dehydrogenase and DnaK) were identified under both planktonic and biofilm growth conditions. In conclusion, the protein expression pattern of SS, grown as biofilm, was different from the SS grown as planktonic cells. These five immunogenic proteins that were specific to SS biofilm cells may potentially be targeted as vaccine candidates to protect against SS biofilm infections. The four proteins common to both biofilm and planktonic cells can be targeted as vaccine candidates to protect against both biofilm and acute infections.