The Interaction between Phagocytes and Streptococcus agalactiae (GBS) Mediated by the Activated Complement System is the Key to GBS Inducing Acute Bacterial Meningitis of Tilapia

The impact of lysine succinylation modification of host factor for RNA phage Qβ replicase at K56 site on the biological functions of Aeromonas hydrophila

Post-translational modifications (PTMs) play pivotal roles in modulating protein functions. In Aeromonas hydrophila, a freshwater Gram-negative pathogen threatening human and animal health, the host factor for RNA phage Qβ replicase (Hfq) is a key regulatory protein. Its K56 site undergoes succinylation modification, suggesting important functions. However, the exact roles of Hfq and its K56 site in A. hydrophila were unclear. Our physiological assays showed that hfq deletion increased protease activity and motility, but reduced biofilm formation, chemotaxis, stress response, and antibiotic resistance. K56 succinylation enhanced protease activity and biofilm formation, and altered chemotaxis. Comprehensive transcriptome and proteome analysis further revealed that hfq deletion led to an increase in 11 peptidases and 8 flagellar proteins, as well as a decrease in 5 stress-related proteins. It also suppressed the pathways involved in chemotaxis and beta-lactam resistance. On the other hand, K56 succinylation enhanced fatty acid synthesis pathway and the expression of methyl-accepting chemotaxis proteins (MCPs). Consistent with the omics data, qPCR validation confirmed the expression of 12 genes, including metalloprotease and MCPs. Overall, this study deepened insights into Hfq regulation in A. hydrophila and revealed the previously unknown molecular switch function of post-translational modifications (PTMs) on this protein.

Uncovering the pathogenic mechanisms of Cronobacter turicensis: A dual transcriptomics study using a zebrafish larvae model

PURPOSE

Cronobacter (C.) is an emerging opportunistic pathogen representing a significant cause of mortality in neonatal patients with bacteremia and meningitis. The pathobiology of Cronobacter mediated meningitis has primarily been investigated using in vitro models. In this study, we used zebrafish to investigate in vivo the infection strategy of the sepsis/meningitis-causing strain C. turicensis z3032 (LMG 23827T) and the immune response of zebrafish larvae after central nervous system (CNS) invasion. Global gene expression profiles of both organisms were analyzed using RNA-Seq.

METHODS

Injection of bacteria into the yolk sac resulted in proliferation of bacteria and translocation to different tissues, including the brain. Infected larval heads were obtained by microdissection and dual RNA-sequencing was performed on host and pathogen simultaneously.

RESULTS

A total of 1432 genes in C. turicensis z3032 and 80 genes in zebrafish were found to be differentially expressed. Upregulated virulence genes in C. turicensis included those encoding for denitrification and anaerobic respiration, chemotaxis, surface structures, and secretion systems. In zebrafish, transcriptional changes included inflammatory processes, cytokine mediated signaling pathways, and NF-kB signaling as the primary GO categories for upregulated genes in response to infection.

CONCLUSION

The dual transcriptomics approach provided a unique opportunity to create a comprehensive catalog of differentially expressed genes in both the pathogen and the host, offering new insights into the infection strategies of C. turicensis and zebrafish immune response.

Protease SfpB plays an important role in cell membrane stability and immune system evasion in Streptococcus agalactiae

Bacteria possess the ability to develop diverse and ingenious strategies to outwit the host immune system, and proteases are one of the many weapons employed by bacteria. This study sought to identify S. agalactiae additional serine protease and determine its role in virulence. The S. agalactiae THN0901 genome features one S8 family serine peptidase B (SfpB), acting as a secreted and externally exposed entity. A S8 family serine peptidase mutant strain (ΔsfpB) and complement strain (CΔsfpB) were generated through homologous recombination. Compared to the wild-type strain THN0901, the absorption of EtBr dyes was significantly reduced (P < 0.01) in ΔsfpB, implying an altered cell membrane permeability. In addition, the ΔsfpB strain had a significantly lower survival rate in macrophages (P < 0.01) and a 61.85 % lower adhesion ability to the EPC cells (P < 0.01) compared to THN0901. In the in vivo colonization experiment using tilapia as a model, 210 fish were selected and injected with different bacterial strains at a concentration of 3 × 106 CFU/tail. At 6, 12, 24, 48, 72 and 96 h post-injection, three fish were randomly selected from each group and their brain, liver, spleen, and kidney tissues were isolated. Subsequently, it was demonstrated that the ΔsfpB strain exhibited a markedly diminished capacity for colonization in tilapia. Additionally, the cumulative mortality of ΔsfpB in fish after intraperitoneal injection was reduced by 19.92-23.85 %. In conclusion, the findings in this study have demonstrated that the SfpB plays a significant role in S. agalactiae cell membrane stability and immune evasion. The immune evasion is fundamental for the development and transmission of invasive diseases, the serine protease SfpB may be a promising candidate for the development of antimicrobial agents to reduce the transmission of S. agalactiae.

Current research update on group B streptococcal infection related to obstetrics and gynecology

Group B streptococcal (GBS) is a Gram-positive bacterium that is commonly found in the gastrointestinal tract and urogenital tract. GBS infestation during pregnancy is a significant contributor to maternal and neonatal morbidity and mortality globally. This article aims to discuss the infectious diseases caused by GBS in the field of obstetrics and gynecology, as well as the challenges associated with the detection, treatment, and prevention of GBS.

Pathogenic bacteria prevalence in cultured Nile tilapia in Southwest Mexico: A real-time PCR analysis

The present study investigates molecular-based PCR techniques to estimate the prevalence of fish pathogens in southwest Mexico where recurrent mortality in the tilapia cultures has been observed. Sample of internal organs and lesions of Nile tilapia were taken and analysed in 2018, 2019, 2020 and 2022 to detect bacterial pathogens using PCR. No samples were taken in 2021 due to the COVID-19 pandemic. The real-time PCR conditions were optimized to allow a qualitative reliable detection of the bacteria from fixed fish tissue. A total of 599 pond- and cage-cultured tilapia from the southwestern Mexican Pacific (Guerrero, Oaxaca and Chiapas states) were analysed. In this tropical region, during 2018 and 2019 water temperatures of the tilapia cultures were generally with the optimal range to grow Nile tilapia, although extreme values were recorded on some farms. Most of the tilapia sampled were apparently healthy. No Francisella sp. was detected in any sample, and Staphylococcus sp. was the most prevalent (from 0% to 64%) bacteria from the three states over time. Low prevalence of Aeromonas sp. was found, from 0% to 4.3%, although the fish pathogen Aeromonas dhakensis was not detected. Sterptococcus iniae was only detected in Chiapas in 2019 at a low prevalence (1.4%), while the major tilapia pathogen S. agalactiae was detected at a high prevalence (from 0% to 59%) in the three Mexican states. This is the first detection of these pathogenic bacteria in rural farms using real-time PCR and constitutes a great risk for tilapia aquaculture in Mexico, as well as a potential dispersion of these pathogens to other aquaculture areas.

BNC-rSS, a bivalent subunit nanovaccine affords the cross-protection against Streptococcus agalactiae and Streptococcus iniae infection in tilapia

Streptococcal disease has severely restricted the development of global tilapia industry, which is mainly caused by Streptococcus agalactiae (S. agalactiae) and Streptococcus iniae (S. iniae). Vaccination has been proved to be a potential strategy to control it. In this study, a multi-epitope subunit vaccine Sip-Srr (SS) was prepared based on the B-cell antigenic epitopes prediction and multiple sequence alignment analysis of Sip and Srr sequences. Furthermore, the BNC-rSS nanocarrier vaccine system was constructed by connecting the rSS protein with modified bacterial nanocellulose (BNCs) and characterized by Fourier Transform Infrared Spectroscopy and Scanning Electron Microscope, the immersion immune effect against S. agalactiae and S. iniae infection was evaluated. The results showed that compared with the control group, BNC-rSS significantly enhanced serum antibody production, related enzyme activities and immune-related genes expression. It was noteworthy that BNC-rSS vaccine improved immune protection of tilapia, with survival rates of 66.67 % (S. agalactiae) and 60.00 % (S. iniae), respectively, compared with those of rSS vaccine (30 % and 33.33 %, respectively). Our study indicated that the BNC-rSS nanovaccine could elicit robust immune responses in tilapia by immersion immunization, and had the potential to offer cross-protection against S. agalactiae and S. iniae infection in tilapia.

Exploring the underlying molecular mechanism of tri(1,3-dichloropropyl) phosphate-induced neurodevelopmental toxicity via thyroid hormone disruption in zebrafish by multi-omics analysis

Tri(1,3-dichloropropyl) phosphate (TDCPP) is widespread in the environment as a typical thyroid hormone-disrupting chemical. Here, we aimed to explore the toxicological mechanisms of the thyroid hormone-disrupting effects induced by TDCPP in zebrafish embryos/larvae using multi-omics analysis. The results showed that TDCPP (400 and 600 µg/L) induced phenotypic alteration and thyroid hormone imbalance in zebrafish larvae. It resulted in behavioral abnormalities during zebrafish embryonic development, suggesting that this chemical might exhibit neurodevelopmental toxicity. Transcriptomic and proteomic analysis provided consistent evidence at the gene and protein levels that neurodevelopmental disorders were significantly enhanced by TDCPP exposure (p < 0.05). Additionally, multi-omics data indicated that membrane thyroid hormone receptor (mTR)-mediated non-genomic pathways, including cell communication (ECM-receptor interactions, focal adhesion, etc.) and signal transduction pathways (MAPK signaling pathway, calcium signaling pathway, neuroactive ligand-receptor interaction pathway, etc.), were significantly disturbed (p < 0.05) and might contribute to the neurodevelopmental toxicity induced by TDCPP. Therefore, behavioral abnormalities and neurodevelopmental disorders might be important phenotypic characteristics of TDCPP-induced thyroid hormone disruption, and mTR-mediated non-genomic networks might participate in the disruptive effects of this chemical. This study provides new insights into the toxicological mechanisms of TDCPP-induced thyroid hormone disruption and proposes a theoretical basis for risk management of this chemical.

Applying genetic technologies to combat infectious diseases in aquaculture

Disease and parasitism cause major welfare, environmental and economic concerns for global aquaculture. In this review, we examine the status and potential of technologies that exploit genetic variation in host resistance to tackle this problem. We argue that there is an urgent need to improve understanding of the genetic mechanisms involved, leading to the development of tools that can be applied to boost host resistance and reduce the disease burden. We draw on two pressing global disease problems as case studies-sea lice infestations in salmonids and white spot syndrome in shrimp. We review how the latest genetic technologies can be capitalised upon to determine the mechanisms underlying inter- and intra-species variation in pathogen/parasite resistance, and how the derived knowledge could be applied to boost disease resistance using selective breeding, gene editing and/or with targeted feed treatments and vaccines. Gene editing brings novel opportunities, but also implementation and dissemination challenges, and necessitates new protocols to integrate the technology into aquaculture breeding programmes. There is also an ongoing need to minimise risks of disease agents evolving to overcome genetic improvements to host resistance, and insights from epidemiological and evolutionary models of pathogen infestation in wild and cultured host populations are explored. Ethical issues around the different approaches for achieving genetic resistance are discussed. Application of genetic technologies and approaches has potential to improve fundamental knowledge of mechanisms affecting genetic resistance and provide effective pathways for implementation that could lead to more resistant aquaculture stocks, transforming global aquaculture.

Dual RNA sequencing of group B Streptococcus-infected human monocytes reveals new insights into host-pathogen interactions and bacterial evasion of phagocytosis

Streptococcus agalactiae, also known as Group B Streptococcus (GBS) is a frequent cause of infections, including bacteraemia and other acute diseases in adults and immunocompromised individuals. We developed a novel system to study GBS within human monocytes to define the co-transcriptome of intracellular GBS (iGBS) and host cells simultaneously using dual RNA-sequencing (RNA-seq) to better define how this pathogen responds to host cells. Using human U937 monocytes and genome-sequenced GBS reference strain 874,391 in antibiotic protection assays we validated a system for dual-RNA seq based on measures of GBS and monocyte viability to ensure that the bacterial and host cell co-transcriptome reflected mainly intracellular (iGBS) rather than extracellular GBS. Elucidation of the co-transcriptome revealed 1119 dysregulated transcripts in iGBS with most genes, including several that encode virulence factors (e.g., scpB, hvgA, ribD, pil2b) exhibiting activation by upregulated expression. Infection with iGBS resulted in significant remodelling of the monocyte transcriptome, with 7587 transcripts differentially expressed including 7040 up-regulated and 547 down-regulated. qPCR confirmed that the most strongly activated genes included sht, encoding Streptococcal Histidine Triad Protein. An isogenic GBS mutant strain deficient in sht revealed a significant effect of this gene on phagocytosis of GBS and survival of the bacteria during systemic infection in mice. Identification of a novel contribution of sht to GBS virulence shows the co-transcriptome responses elucidated in GBS-infected monocytes help to shape the host-pathogen interaction and establish a role for sht in the response of the bacteria to phagocytic uptake. This study provides comprehension of concurrent transcriptional responses that occur in GBS and human monocytes that shape the host-pathogen interaction.

Molecular Characteristics and Quantitative Proteomic Analysis of Klebsiella pneumoniae Strains with Carbapenem and Colistin Resistance

Carbapenem-resistant Klebsiella pneumoniae (CRKP) are usually multidrug resistant (MDR) and cause serious therapeutic problems. Colistin is a critical last-resort therapeutic option for MDR bacterial infections. However, increasing colistin use has led to the emergence of extensively drug-resistant (XDR) strains, raising a significant challenge for healthcare. In order to gain insight into the antibiotic resistance mechanisms of CRKP and identify potential drug targets, we compared the molecular characteristics and the proteomes among drug-sensitive (DS), MDR, and XDR K. pneumoniae strains. All drug-resistant isolates belonged to ST11, harboring bla_KPC and hypervirulent genes. None of the plasmid-encoded mcr genes were detected in the colistin-resistant XDR strains. Through a tandem mass tag (TMT)-labeled proteomic technique, a total of 3531 proteins were identified in the current study. Compared to the DS strains, there were 247 differentially expressed proteins (DEPs) in the MDR strains and 346 DEPs in the XDR strains, respectively. Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis revealed that a majority of the DEPs were involved in various metabolic pathways, which were beneficial to the evolution of drug resistance in K. pneumoniae. In addition, a total of 67 DEPs were identified between the MDR and XDR strains. KEGG enrichment and protein-protein interaction network analysis showed their participation in cationic antimicrobial peptide resistance and two-component systems. In conclusion, our results highlight the emergence of colistin-resistant and hypervirulent CRKP, which is a noticeable superbug. The DEPs identified in our study are of great significance for the exploration of effective control strategies against infections of CRKP.

Nongenomic effects and mechanistic study of butyl benzyl phthalate-induced thyroid disruption: Based on integrated in vitro, in silico assays and proteome analysis

Based on in vitro and in silico assays as well as proteome analysis, this study explored the nongenomic mechanism for butyl benzyl phthalate (BBP)-induced thyroid disruption. Molecular docking simulations showed that BBP could dock into the Arg-Gly-Asp (RGD) domain of integrin α_vβ₃ and form hydrogen bonds with a docking energy of -35.80 kcal/mol. This chemical enhanced rat pituitary tumor cell (GH3) proliferation and exhibited thyroid hormone-disrupting effects at 5-10 μmol/L. Meanwhile, BBP upregulated β₃ gene expression and activated the downstream mitogen-activated protein kinase (MAPK) pathway in GH3 cells. Interestingly, GH3 cell proliferation was attenuated by integrin α_vβ₃ inhibitor (RGD peptide) or ERK1/2 inhibitor (PD98059), suggesting that the disruptions might be partly attributed to its interaction with integrin α_vβ₃ and activation of MAPK. Furthermore, quantitative proteomic analysis of zebrafish embryos exposed to BBP at an environmentally relevant concentration of 0.3 μmol/L revealed that BBP perturbed proteins and pathways related to cell communication (e.g., integrin binding) and signal transduction (e.g., MAPK signaling pathway). Taken together, our results supported that the biological effects of BBP-activated integrin α_vβ₃ mediated by the nongenomic pathway play an important role in its thyroid disruption. CAPSULE: The nongenomic pathway plays a vital role in the thyroid disruption-inducing actions of BBP.

Acetylome and Succinylome Profiling of Edwardsiella tarda Reveals Key Roles of Both Lysine Acylations in Bacterial Antibiotic Resistance

The antibiotic resistance of Edwardsiella tarda is becoming increasingly prevalent, and thus novel antimicrobial strategies are being sought. Lysine acylation has been demonstrated to play an important role in bacterial physiological functions, while its role in bacterial antibiotic resistance remains largely unclear. In this study, we investigated the lysine acetylation and succinylation profiles of E. tarda strain EIB202 using affinity antibody purification combined with LC-MS/MS. A total of 1511 lysine-acetylation sites were identified on 589 proteins, and 2346 lysine-succinylation sites were further identified on 692 proteins of this pathogen. Further bioinformatic analysis showed that both post-translational modifications (PTMs) were enriched in the tricarboxylic acid (TCA) cycle, pyruvate metabolism, biosynthesis, and carbon metabolism. In addition, 948 peptides of 437 proteins had overlapping associations with multiple metabolic pathways. Moreover, both acetylation and succinylation were found in many antimicrobial resistance (AMR) proteins, suggesting their potentially vital roles in antibiotic resistance. In general, our work provides insights into the acetylome and succinylome features responsible for the antibiotic resistance mechanism of E. tarda, and the results may facilitate future investigations into the pathogenesis of this bacterium.

Thyroid Hormone Disruption by Organophosphate Esters Is Mediated by Nuclear/Membrane Thyroid Hormone Receptors: In Vitro, In Vivo, and In Silico Studies

Earlier mechanistic studies of many prohibited flame retardants (FRs) highlighted their thyroid hormone-disrupting activity through nuclear thyroid hormone receptors (nTRs), whereas some alternative FRs such as organophosphate esters (OPEs) exerted weak nTR-disrupting effects. However, an increasing number of studies have revealed that OPEs also exert thyroid hormone-disrupting effects, and the underlying mechanism is unclear. Herein, the thyroid hormone-disrupting effects and mechanisms of 8 typical OPEs were investigated using integrated in vitro, in vivo, and in silico assays. All tested chemicals competitively bound to the membrane thyroid hormone receptor (mTR) [the 20% relative inhibitory concentration (RIC20): (3.5 ± 0.2) × 10¹ to (4.9 ± 1.0) × 10⁷ nM], and Cl-OPEs and alkyl-OPEs had lower RIC20 values. In contrast, only 4 OPEs showed nTR antagonistic activities at higher concentrations [≥ (4.8 ± 0.8) × 10³ nM]. Cl-OPEs and alkyl-OPEs preferentially interacted with mTR. Molecular docking illustrated that OPEs docked into mTRs, consistent with the competitive binding assay. In vivo analyses of zebrafish embryonic development confirmed that tris(1,3-dichloro-2-propyl) phosphate induced inappropriate expression of proteins, and these protein interactions might be associated with mTR according to the quantitative proteomic analysis. Based on the results, mTR might play a critical role in mediating the thyroid hormone-disrupting effects of OPEs.

LECT2 Protects Nile Tilapia (Oreochromis niloticus) Against Streptococcus agalatiae Infection

Leukocyte cell-derived chemotaxin 2 (LECT2) is a multifunctional cytokine that especially plays an important role in innate immune. However, the roles of LECT2 in the immune response of the economically important fish Nile tilapia (Oreochromis niloticus) against bacterial infection remains unclear. In this study, a lect2 gene from Nile tilapia (On-lect2) was identified, and its roles in the fish’s immune response against bacterial infection were determined and characterised. On-lect2 contains an open reading frame of 456 bp that encodes a peptide of 151 amino acids, as well as the conservative peptidase M23 domain. On-LECT2 is 62%–84% identical to other fish species and about 50% identical to mammals. The highest transcriptional level of On-lect2 was detected in the liver, whereas the lowest levels were detected in the other tissues. Moreover, the On-LECT2 protein is located mainly in the brain and head kidney. The transcriptional levels of On-lect2 substantially increased in the head kidney, brain, liver and spleen after Streptococcus agalactiae infection. Knockdown On-lect2 led to higher mortality due to liver necrosis or haemorrhage and splenomegaly. In vitro analysis indicated that the recombinant protein of On-LECT2 improved phagocytic activity of head kidney-derived macrophages. In vivo challenge experiments revealed several functions of On-LECT2 in the immune response of Nile tilapia against bacterial infection, including promotion of inflammation, reduction of tissue damages and improvement of survival rate.

Research Advances on Tilapia Streptococcosis

Streptococcus agalactiae, often referred to as group B streptococci (GBS), is a severe pathogen that can infect humans as well as other animals, including tilapia, which is extremely popular in commercial aquaculture. This pathogen causes enormous pecuniary loss, and typical symptoms of streptococcosis—the disease caused by S. agalactiae—include abnormal behavior, exophthalmos, and meningitis, among others. Multiple studies have examined virulence factors associated with S. agalactiae infection, and vaccines were explored, including studies of subunit vaccines. Known virulence factors include capsular polysaccharide (CPS), hemolysin, Christie-Atkins-Munch-Peterson (CAMP) factor, hyaluronidase (HAase), superoxide dismutase (SOD), and serine-threonine protein kinase (STPK), and effective vaccine antigens reported to date include GapA, Sip, OCT, PGK, FbsA, and EF-Tu. In this review, I summarize findings from several studies about the etiology, pathology, virulence factors, and vaccine prospects for S. agalactiae. I end by considering which research areas are likely to yield success in the prevention and treatment of tilapia streptococcosis.

Transmembrane transport mechanism of n-hexadecane by Candida tropicalis: Kinetic study and proteomic analysis

Yeasts are the most predominant petroleum hydrocarbon-degrading fungi isolated from petroleum-contaminated soil. However, information of the transmembrane transport of petroleum hydrocarbon into yeast cells is limited. The present study was designed to explore the transmembrane transport mechanisms of the typical petroleum hydrocarbon n-hexadecane in Candida tropicalis cells with petroleum hydrocarbon biodegradation potential. Yeast cells were treated with n-hexadecane in different scenarios, and the percentage of intracellular n-hexadecane and transport dynamics were investigated accordingly. The intracellular concentration of n-hexadecane increased within 15 min, and transportation was inhibited by NaN₃, an ATPase inhibitor. The uptake kinetics of n-hexadecane were well fitted by the Michaelis-Menten model, and Kt values ranged from 152.49 to 194.93 mg/L. All these findings indicated that n-hexadecane might cross the yeast cells in an energy-dependent manner and exhibit an affinity with the cell transport system. Moreover, the differentially expressed membrane proteins induced by n-hexadecane were identified and quantified by tandem mass tag labeling coupled with liquid chromatography tandem mass spectrometry analysis. The proteome analysis results demonstrated that energy production and conversion accounted for a large proportion of the functional classifications of the differentially expressed proteins, providing further evidence that sufficient energy supply is essential for transmembrane transport. Protein functional analysis also suggested that differentially expressed proteins associated with transmembrane transport processes are clearly enriched in endocytosis and phagosome pathways (p < 0.05), and the analysis supported the notion that the underlying transmembrane transport mechanism might be associated with endocytosis and phagosome pathways, revealing a new mechanism of n-hexadecane internalization by Candida tropicalis.