Streptococcus pneumoniae Cell Wall-Localized Trigger Factor Elicits a Protective Immune Response and Contributes to Bacterial Adhesion to the Host

Serotype-Switch Variant of Multidrug-Resistant Streptococcus pneumoniae Sequence Type 271

We discovered 3 invasive, multidrug-resistant Streptococcus pneumoniae isolates of vaccine-refractory capsular serotype 3 that recently arose within the successful sequence type 271 complex through a serotype switch recombination event. Mapping genomic recombination sites within the serotype 3/sequence type 271 progeny revealed a 55.9-kb donated fragment that encompassed cps3, pbp1a, and additional virulence factors.

Whole-genome analysis of probiotic product isolates reveals the presence of genes related to antimicrobial resistance, virulence factors, and toxic metabolites, posing potential health risks

Background

Safety issues of probiotic products have been reported frequently in recent years. Ten bacterial strains isolated from seven commercial probiotic products on market were evaluated for their safety, by whole-genome analysis.

Results

We found that the bacterial species of three probiotic products were incorrectly labeled. Furthermore, six probiotic product isolates (PPS) contained genes for the production of toxic metabolites, while another three strains contained virulence genes, which might pose a potential health risk. In addition, three of them have drug-resistance genes, among which two strains potentially displayed multidrug resistance. One isolate has in silico predicted transferable genes responsible for toxic metabolite production, and they could potentially transfer to human gut microflora or environmental bacteria. Isolates of Lactobacillus rhamnosus and Bifidobacterium animalis subsp. lactis are associated with low risk for human consumption. Based on a comparative genome analysis, we found that the isolated Enterococcus faecium TK-P5D clustered with a well-defined probiotic strain, while E. faecalis TK-P4B clustered with a pathogenic strain.

Conclusions

Our work clearly illustrates that whole-genome analysis is a useful method to evaluate the quality and safety of probiotic products. Regulatory quality control and stringent regulations on probiotic products are needed to ensure safe consumption and protect human health.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12864-021-07539-9.

Staphylococcus aureus Trigger Factor Is Involved in Biofilm Formation and Cooperates with the Chaperone PpiB

Peptidyl-prolyl cis/trans isomerases (PPIases) are enzymes that assist in protein folding around proline-peptide bonds, and they often possess chaperone activity. Staphylococcus aureus encodes three PPIases, i.e., PrsA, PpiB, and trigger factor (TF). Previous work by our group demonstrated a role for both PrsA and PpiB in S. aureus; however, TF remains largely unstudied. Here, we identify a role for TF in S. aureus biofilm formation and demonstrate cooperation between TF and the cytoplasmic PPIase PpiB. Mutation of the tig gene (encoding TF) led to reduced biofilm development in vitro but no significant attenuation of virulence in a mouse model of infection. To investigate whether TF possesses chaperone activity, we analyzed the ability of a tig mutant to survive acid and base stress. While there was no significant decrease for a tig mutant, a ppiB tig double mutant exhibited significant decreases in cell viability after acid and base challenges. We then demonstrated that a ppiB tig double mutant had exacerbated phenotypes in vitro and in vivo, compared to either single mutant. Finally, in vivo immunoprecipitation of epitope-tagged PpiB revealed that PpiB interacted with 4 times the number of proteins when TF was absent from the cell, suggesting that it may be compensating for the loss of TF. Interestingly, the only proteins found to interact with TF were TF itself, fibronectin-binding protein B (FnBPB), and the chaperone protein ClpB. Collectively, these results support the first phenotype for S. aureus TF and demonstrate a greater network of cooperation between chaperone proteins in Staphylococcus aureus IMPORTANCE S. aureus encodes a large number of virulence factors that aid the bacterium in survival and pathogenesis. These virulence factors have a wide variety of functions; however, they must all be properly secreted in order to be functional. Bacterial chaperone proteins often assist in secretion by trafficking proteins to secretion machinery or assisting in proper protein folding. Here, we report that the S. aureus chaperone TF contributes to biofilm formation and cooperates with the chaperone PpiB to regulate S. aureus virulence processes. These data highlight the first known role for TF in S. aureus and suggest that S. aureus chaperone proteins may be involved in a greater regulatory network in the cell.

Identification of conditionally essential genes for Streptococcus suis infection in pigs

Streptococcus suis

is a Gram-positive bacterium and zoonotic pathogen that causes meningitis and sepsis in pigs and humans. The aim of this study was to identify genes required for S. suis infection. We created Tn-Seq libraries in a virulent S. suis strain 10, which was used to inoculate pigs in an intrathecal experimental infection. Comparative analysis of the relative abundance of mutants recovered from different sites of infection (blood, cerebrospinal fluid, and meninges of the brain) identified 361 conditionally essential genes, i.e. required for infection, which is about 18% of the genome. The conditionally essential genes were primarily involved in metabolic and transport processes, regulation, ribosomal structure and biogenesis, transcription, and cell wall membrane and envelope biogenesis, stress defenses, and immune evasion. Directed mutants were created in a set of 10 genes of different genetic ontologies and their role was determined in ex vivo models. Mutants showed different levels of sensitivity to survival in whole blood, serum, cerebrospinal fluid, thermic shock, and stress conditions, as compared to the wild type. Additionally, the role of three selected mutants was validated in co-infection experiments in which pigs were infected with both wild type and isogenic mutant strains. The genetic determinants of infection identified in this work contribute to novel insights in S. suis pathogenesis and could serve as targets for novel vaccines or antimicrobial drugs.

Immunization With a Combination of Four Recombinant Brucella abortus Proteins Omp16, Omp19, Omp28, and L7/L12 Induces T Helper 1 Immune Response Against Virulent B. abortus 544 Infection in BALB/c Mice

Protective efficiency of a combination of four recombinant Brucella abortus (B. abortus) proteins, namely outer membrane protein (Omp) 16, Omp19, Omp28, and 50S ribosomal protein L7/L12 was evaluated as a combined subunit vaccine (CSV) against B. abortus infection in RAW 264.7 cell line and murine model. The immunoreactivity of these four recombinant proteins as well as pCold-TF vector reacted with Brucella-positive serum individually, but not with Brucella-negative serum by immunoblotting assay. CSV-treated RAW 264.7 cells significantly induced production of IFN-γ and IL-12 while decreased IL-10 production at the late stage of infection compared to PBS-treated control cells. In addition, the enhancement of nitric oxide production together with cytokines secretion profile in CSV-treated cells proved that CSV notably activated bactericidal mechanisms in macrophages. Consistently, mice immunized with CSV strongly elicited production of pro-inflammatory cytokines TNF-α, IL-6 and MCP-1 compared to PBS control group. Moreover, the concentration of IFN-γ was >IL-10 and titers of IgG2a were also heightened compared to IgG1 in CSV-immunized mice which suggest that CSV induced predominantly T helper 1 T cell. These results suggest that the CSV used in the present study is a potential candidate as a preventive therapy against brucellosis.

Trigger Factor in Association with the ClpP1P2 Heterocomplex of Leptospira Promotes Protease/Peptidase Activity

The genomic analysis of Leptospira reveals a trigger factor (TF) encoding gene (tig) to be colocalized along with the clpP1 and clpX. The TF is a crouching dragon-like protein known to be a ribosome-associated chaperone that is involved in cotranslational protein folding in bacteria in an ATP-independent mode. In Leptospira, tig is localized upstream of the clpP1 with a short (4 bp) overlap. In the present study, we document the distinctive role of Leptospira TF (LinTF) in the caseinolytic protease (ClpP) system. The recombinant LinTF (rLinTF) was found to improve the peptidase or protease activity of the ClpP1P2 heterocomplex and ClpXP1P2 complex, respectively, on model substrates. In addition, on supplementation of rLinTF to rClpP1P2 bound to its physiological ATPase chaperone ClpX or the antibiotic analogue acyldepsipeptide (ADEP), an augmentation in the activity of ClpP1P2 was observed. These studies underscore the novel role of LinTF in aiding the caseinolytic protease activity of Leptospira. Supplementation of rLinTF to a peptidase assay of rClpP1P2 conditionally in the presence of a salt (sodium citrate) with high Hofmeister strength led us to speculate that rLinTF may have a role in the assembly of multimeric proteins. The deletion of one of the arms (arm-2) of the LinTF structure from the carboxy terminal domain indicated a reduction in its capacity to stimulate rClpP1P2 activity. Thus, the C-terminal domain of LinTF may have a role in the assembly of multimeric ClpP protein, leading to enhancement of ClpP activity.

Immunogenicity and protective response induced by recombinant Brucella abortus proteins Adk, SecB and combination of these two recombinant proteins against a virulent strain B. abortus 544 infection in BALB/c mice

In this study, two recombinant proteins encoded by Brucella abortus genes Adk and SecB were evaluated as single subunit vaccine (SSV) as well as combined subunit vaccine (CSV) against B. abortus infection in BALB/c mice. These genes were cloned into pcold-TF expression system and recombinant proteins were expressed in Escherichia coli DH5α. The immunoreactivity of purified rAdk and rSecB was analyzed by immunoblotting showing that purified rAdk and rSecB as well as pcold-TF vector strongly reacted with Brucella-positive serum. Mice were immunized intraperitoneally with SSVs, CSV, pcold-TF, RB51 and PBS. The analysis of cytokine revealed that SSVs and CSV can strongly induce production of proinflammatory cytokines TNF and IL-6, suggesting that these subunit vaccines elicited innate immune response, particularly, activated antimicrobial mechanism of macrophages to limit the initial infection. On the other hand, immunization with SSVs and CSV elicited strong IFN-γ production and decreased IL-10 production compared to PBS group. The secretion profiles of IFN-γ and IL-10 together with an enhancement of blood CD4⁺ population and significantly induced specific IgG1 and IgG2a antibodies indicated that SSVs and CSV induced not only humoral immunity but also T helper 1 T cell immunity. Finally, spleen proliferation and bacterial burden in the spleen of mice vaccinated with these subunit vaccines were significantly lower than those of PBS group, which conferred significant protection against B. abortus infection. Altogether, the potential of these antigens of B. abortus could be prospective candidates to develop subunit vaccines against brucellosis.

Streptococcus pneumoniae inhibits purinergic signaling and promotes purinergic receptor P2Y2 internalization in alveolar epithelial cells

Bacterial pneumonia is a global health challenge that causes up to 2 million deaths each year. Purinergic signaling plays a pivotal role in healthy alveolar epithelium. Here, we used fluorophore-based analysis and live-cell calcium imaging to address the question of whether the bacterial pathogen Streptococcus pneumoniae directly interferes with purinergic signaling in alveolar epithelial cells. Disturbed purinergic signaling might result in pathophysiologic changes like edema formation and atelectasis, which are commonly seen in bacterial pneumonia. Purine receptors are mainly activated by ATP, mediating a cytosolic calcium response. We found that this purinergic receptor P2Y₂-mediated response is suppressed in the presence of S. pneumoniae in A549 and isolated primary alveolar cells in a temperature-dependent manner. Downstream inositol 3-phosphate (IP₃) signaling appeared to be unaffected, as calcium signaling via protease-activated receptor 2 remained unaltered. S. pneumoniae-induced suppression of the P2Y₂-mediated calcium response depended on the P2Y₂ phosphorylation sites Ser-243, Thr-344, and Ser-356, which are involved in receptor desensitization and internalization. Spinning-disk live-cell imaging revealed that S. pneumoniae induces P2Y₂ translocation into the cytosol. In conclusion, our results show that S. pneumoniae directly inhibits purinergic signaling by inducing P2Y₂ phosphorylation and internalization, resulting in the suppression of the calcium response of alveolar epithelial cells to ATP, thereby affecting cellular integrity and function.