Genotyping of Streptococcus agalactiae strains isolated from fish, human and cattle and their virulence potential in Nile tilapia

Comparative analysis of T-cell immunity between Streptococcus agalactiae susceptible and resistant tilapia (Oreochromis niloticus)

Nile tilapia (Oreochromis niloticus) is one of the important economic fish species cultured worldwide. However, Streptococcus agalactiae has emerged as a significant bacterial threat, severely impacting the economy of tilapia industry. The immune response underlying the resistance of tilapia to S. agalactiae are not well understood, hindering the reasonable evaluation of breeding and the formulation of effective strategies. In this study, we investigated the differences in T-cell immunity between S. agalactiae-resistant and -susceptible tilapia. Compared with susceptible tilapia, resistant tilapia exhibited a higher percentage of T cells and BrdU+ T cells during infection, indicating a superior proliferative capacity. Whether infected or not, T cells from resistant fish demonstrated a greater ability to resist apoptosis. Additionally, T cell effector genes, including interleukin (IL)-2, interferon (IFN)-γ, perforin A, and granzyme B were expressed at higher levels in resistant tilapia after infection. Along with these T-cell immune responses, resistant fish showed more effective clearance of infection. Our study elucidates the T-cell immune responses in resistant tilapia, which may contribute to the high resistance of tilapia to S. agalactiae, and providing valuable theoretical references for the selection and evaluation of disease-resistant fish strains in the future.

First report of Streptococcus agalactiae isolated from a healthy captive sichuan golden snub-nosed monkey (Rhinopithecus roxellana) in China

Streptococcus agalactiae (S. agalactiae) is an opportunistic pathogen, and to date, studies have mainly focused on S. agalactiae strains isolated from humans, dairy cows, and fish. We reported one S. agalactiae strain, named CFFB, which was isolated from a healthy Sichuan golden snub-nosed monkey. Classical bacteriological approaches, as well as, next-generation sequencing, comparative genomics, and mice challenge test were used to characterize this strain. CFFB was identified as serotype III, ST19 combination which is a common type found in human strains. Phylogenetic analysis showed that the genome of CFFB was closely related to human clinical isolates, rather far away from animal strains. In total, CFFB contained fewer virulence-associated genes and antibiotic resistance genes than human isolates that were close to CFFB in evolutionary relationships. In the mice challenge test, CFFB had a relative weak virulence that just caused death in 33 % of ICR mice at a dose of 108 CFU by intraperitoneal injection, and CFFB was reisolated from the cardiac blood of the dead mice. Meanwhile, two intact prophages (prophage 1 and 2) were identified in the CFFB genome and shared high similarities with phage Javan52 and Javan29 which from human S. agalactiae isolate Gottschalk 1002A and RBH03, respectively. Moreover, the type II-A CRISPR-Cas system was detected in the CFFB genome, and the spacers from CFFB were the same to the streptococci isolates from human. These results suggest that CFFB isolated from healthy Sichuan golden snub-nosed monkeys may have its origin in human S. agalactiae. Our results suggested some genomic similarities between the S. agalactiae colonized in Sichuan golden snub-nosed monkey and those in infected humans.

Antibacterial activity and mechanism of chelerythrine against Streptococcus agalactiae

Streptococcus agalactiae (S.agalactiae), also known as group B Streptococcus (GBS), is a highly infectious pathogen. Prolonged antibiotic usage leads to significant issues of antibiotic residue and resistance. Chelerythrine (CHE) is a naturally occurring benzophenidine alkaloid and chelerythrine chloride (CHEC) is its hydrochloride form with diverse biological and pharmacological activities. However, the antibacterial mechanism of CHEC against GBS remains unclear. Thus, this study aims to investigate the in vitro antibacterial activity of CHEC on GBS and elucidate its underlying mechanism. The antibacterial effect of CHEC on GBS was assessed using inhibitory zone, minimum inhibitory concentration (MIC), and minimum bactericidal concentration (MBC) assays, as well as by constructing a time-kill curve. The antibacterial mechanism of CHEC was investigated through techniques such as scanning electron microscopy (SEM) and transmission electron microscopy (TEM), measurement of alkaline phosphatase (AKP) activity, determination of Na+ K+, Ca2+ Mg2+-adenosine triphosphate (ATP) activity, observation of membrane permeability, and analysis of intracellular reactive oxygen species (ROS) and mRNA expression levels of key virulence genes. The results demonstrated that the inhibition zone diameters of CHEC against GBS were 14.32 mm, 12.67 mm, and 10.76 mm at concentrations of 2 mg/mL, 1 mg/mL, and 0.5 mg/mL, respectively. The MIC and MBC values were determined as 256 μg/mL and 512 μg/mL correspondingly. In the time-kill curve, 8 × MIC, 4 × MIC and 2 × MIC CHEC could completely kill GBS within 24 h. SEM and TEM analyses revealed significant morphological alterations in GBS cells treated with CHEC including shrinkage, collapse, and leakage of cellular fluids. Furthermore, the antibacterial mechanism underlying CHEC's efficacy against GBS was attributed to its disruption of cell wall integrity as well as membrane permeability resulting in extracellular release of intracellular ATP, AKP, Na+ K+, Ca2+ Mg2+. Additionally CHEC could increase the ROS production leading to oxidative damage and downregulating mRNA expression levels of key virulence genes in GBS cells. In conclusion, CHEC holds potential as an antimicrobial agent against GBS and further investigations are necessary to elucidate additional molecular mechanisms.

Comparative analysis of Streptococcus agalactiae serotypes Ia and II isolates from China and Pakistan in a murine model: A focus on pathogenesis and immune response

Bovine mastitis, caused by Streptococcus agalactiae (Group B Streptococcus; GBS), poses significant economic challenges to the global dairy industry. Mouse models serves as valuable tools for assessing GBS-induced infections as an alternative to large animals. This study aimed to investigate the LD50 dose, organ bacterial load, and quantification of peritoneal leukocyte populations for GBS serotypes Ia and II isolates from China and Pakistan. Additionally, we measured indicators such as lactoferrin, albumin, and myeloperoxidase (MPO) activity. Pro-inflammatory cytokines (TNF-α, IL-1β, IL-6, and IL-2) and anti-inflammatory cytokines (IL-10 and TGF-β) in serum and tissue samples were evaluated using ELISA and qPCR, respectively. BALB/c mice (4 mice per group) received individual intraperitoneal injections of 100 μl containing specific bacterial inoculum concentrations (ranging from 105 to 109 CFU per mouse) of Chinese and Pakistani GBS isolates (serotypes Ia and II). Control groups received 100 μL of sterile PBS. Results revealed that the LD50 bacterial dose causing 50 % mortality in mice was 107 CFU. The highest bacterial load in all experimental groups was quantified in the peritoneum, followed by blood, mammary gland, liver, spleen, lungs, and brain. The most significant bacterial dissemination was observed in mice inoculated with Pakistani serotype Ia at 24 h, with a subsequent notable decline in bacterial counts at day 3. Notably, infection with Pakistani serotype Ia showed a trend of increased total leukocyte counts, significantly higher than Pakistani serotype II, Chinese Serotype Ia, and Chinese serotype II. A substantial influx of neutrophils and lymphocytes was observed in response to all tested serotypes, with Pakistani serotype Ia inducing a significantly higher influx compared to other groups (Pakistani serotype II, Chinese serotype Ia, and Chinese serotype II). Furthermore, TNF-α, IL-1β, IL-2, and IL-6 expressions were significantly increased in mice one day after infection with the Pakistani serotype Ia. Compared to mice infected with the Pakistani serotype II, Chinese Serotype Ia, and Chinese serotype II, those infected with the Pakistani serotype Ia isolate exhibited the highest production of IL-10 and TGF-β, along with significantly increased concentrations of lactoferrin, albumin, and MPO. These findings suggest that the persistence and severity of infection caused by the Pakistani serotype Ia may be linked to its ability to spread to deeper tissues. This study enhances our understanding of the clinical characteristics of bovine mastitis caused by S. agalactiae in China and Pakistan.

Susceptibility Profile and Epidemiological Cut-Off Values Are Influenced by Serotype in Fish Pathogenic Streptococcus agalactiae

Streptococcus agalactiae is a major health concern in tilapia farming worldwide. In contrast to the availability of susceptibility profile results, interpretative criteria for disk diffusion assays and the influence of serotypes on resistance profiles are not available. To address this, sixty isolates (thirty of each serotype, Ib and III) were evaluated using the disk diffusion assay against six antibiotics, and the epidemiological cut-off value (ECV) was calculated. All the isolates were classified as non-wild type (NWT) for sulfamethoxazole (SUT) and norfloxacin (NOR). The inhibition zones for oxytetracycline (OXY) and doxycycline (DOX) were largely distinct; all serotype Ib and III isolates were classified as wild-type (WT) and NWT, respectively. The results for serotype III of fish group B Streptococcus (GBS) were comparable to the NWT tetracycline profile of human GBS available in EUCAST, suggesting the presence of resistance mechanisms in these fish isolates. The calculation of the cut-off wild type (COWT) values for OXY and DOX was appropriate for both serotypes. Differences between the distribution of florfenicol (FLO) and amoxicillin (AMO) were found, and we attribute this to the faster growth rate of serotype III, which promotes smaller inhibition zones. Therefore, using separate COWT for each serotype is necessary. In conclusion, the serotype of fish GBS affects its susceptibility profile, and it is recommended to use serotype-specific COWT values as interpretative criteria for disk diffusion assays against FLO and AMO.

Prophylactic effects of dietary caper (Capparis spinosa) extracts on the control of Streptococcus agalactiae infection, growth, immune-antioxidant, and inflammation cytokine responses of Nile tilapia fingerlings

The antibacterial activity of aqueous (AE) or ethanolic extracts (EE) of caper (Capparis spinosa) against Streptococcus agalactiae was evaluated in vitro. Both caper extracts showed antagonistic activity against S. agalactiae and the inhibition zones in case of ethanolic extracts were larger than those of aqueous ones. Additionally, TEM investigations show that S. agalactiae cells treated with both C. spinosa extracts were damaged and degraded and this damage was greater in case of ethanolic extract. Another study was done to assess the promotion effects of dietary caper (C. spinosa) extracts on growth, antioxidant and immune activity, and inflammation cytokine responses of Nile tilapia (Oreochromis niloticus) and its resistance to S. agalactiae infection. However, fish (40 ± 2 g) were fed on diets containing 1.0 and 2.0 g/kg feed of each caper extract as well as the control group (free of caper) for 6 weeks. Fish were intraperitoneally injected (IP) with Streptococcus agalactiae at the end of the feeding trial, and fish mortality was tracked for additional ten days. Compared with other treatments, fish fed on 2.0 g EE/kg feed had higher counts of white and red blood cells as well as higher hemoglobin levels accompanied with lower AST and ALT activities. Antioxidant (superoxide dismutase and catalase activities) and immune, total protein, globulin, lysozyme, and immunoglobulin M) indices were increased along with significant decline in MDA levels in both caper extracts treated fish groups compared to the control group. Significant promotion in fish growth was affected positively with the increase in both caper extracts; particularly, the larger fish growth was observed in the treatment of 2.0 g EE/kg feed. Expressions of IL-1β and IL-8 were declined; meanwhile levels of IL-10, SOD and CAT genes were upregulated in fish fed on 2.0 g EE/kg feed compared to other groups. After being challenged with S. agalactiae infection, fish survival was considerably (P < 0.05) greater in fish groups that fed on diets with caper extracts; particularly 2.0 g EE/kg feed (75%); while all fish fed on the control one were dead. According to these findings, the antioxidant and immune response of Nile tilapia fingerlings is stimulated by ethanolic extract of caper (2.0 g/kg feed), which also enhanced the growth performance and fish resistance to S. agalactiae infection.

Transcriptome analysis reveals the neuroactive receptor genes response to Streptococcus agalactiae infection in tilapia, Oreochromis niloticus

The detailed crosstalk between the neuroendocrine and immune systems in Oreochromis niloticus, an economically important fish, in response to pathogenic infections, remains unclear. This study revealed the head kidney transcriptional profiles of O. niloticus upon infections with Streptococcus agalactiae, a prevalent pathogen known to cause severe meningitis. Twelve cDNA libraries of O. niloticus head kidney, representing four treatment time points (0, 6, 24, and 48 h), were constructed and a total of 2,528 differentially expressed genes were identified based on pairwise comparisons. KEGG pathway analysis revealed a significant enrichment of the 'neuroactive ligand-receptor interaction' pathway (ko04080), with 13 genes exhibiting differential expression during S. agalactiae infection. Among these, six neuroactive receptor genes (lepr, nr3c1, ptger4, thrb, tspo, and β2-ar) were selected, cloned, and characterized. Although these genes are ubiquitously expressed, and in head kidney leukocytes, their expression was mainly observed in T cells, Mo/Mφ, and NCCs, which are characterized by antimicrobial responses. Furthermore, we examined the response patterns of these six neuroactive receptor genes to gram-positive (S. agalactiae) and gram-negative (Aeromonas hydrophila) bacteria in four different tissues. Notably, lepr, ptger4, tspo, and β2-ar were upregulated in all selected tissues in response to S. agalactiae and A. hydrophila infections. However, nr3c1 and thrb were downregulated in response to S. agalactiae infection in the head kidney and spleen, whereas nr3c1 was upregulated, and thrb was unresponsive to A. hydrophila infection. Our findings provide a theoretical foundation for understanding new links between the neuroendocrine and immune systems during bacterial infection in teleost fish.

Biofilm Formation in Streptococcus agalactiae Is Inhibited by a Small Regulatory RNA Regulated by the Two-Component System CiaRH

Regulatory small RNAs (sRNAs) are involved in the adaptation of bacteria to their environment. CiaR-dependent sRNAs (csRNAs) are controlled by the regulatory two-component system (TCS) CiaRH, which is widely conserved in streptococci. Except for Streptococcus pneumoniae and Streptococcus sanguinis, the targets of these csRNAs have not yet been investigated. Streptococcus agalactiae, the leading cause of neonatal infections, has four conserved csRNA genes, namely, srn015, srn024, srn070, and srn085. Here, we demonstrate the importance of the direct repeat TTTAAG-N5-TTTAAG in the regulation of these csRNAs by CiaRH. A 24-nucleotide Srn024-sap RNA base-pairing region is predicted in silico. The sap gene encodes a LPXTG-cell wall-anchored pullulanase. This protein cleaves α-glucan polysaccharides such as pullulan and glycogen present in the environment to release glucose and is involved in adhesion to human cervical epithelial cells. Inactivation of S. agalactiae pullulanase (SAP) leads to no bacterial growth in a medium with only pullulan as a carbon source and reduced biofilm formation, while deletion of ciaRH and srn024 genes significantly increases bacterial growth and biofilm formation. Using a new translational fusion vector, we demonstrated that Srn024 is involved in the posttranscriptional regulation of sap expression. Complementary base pair exchanges in S. agalactiae suggest that Srn024 interacts directly with sap mRNA and that disruption of this RNA pairing is sufficient to yield the biofilm phenotype of Srn024 deletion. These results suggest the involvement of Srn024 in the adaptation of S. agalactiae to environmental changes and biofilm formation, likely through the regulation of the sap gene. IMPORTANCE Although Streptococcus agalactiae is a commensal bacterium of the human digestive and genitourinary tracts, it is also an opportunistic pathogen for humans and other animals. As the main cause of neonatal infections, it is responsible for pneumonia, bacteremia, and meningitis. However, its adaptation to these different ecological niches is not fully understood. Bacterial regulatory networks are involved in this adaptation, and the regulatory TCSs (e.g., CiaRH), as well as the regulatory sRNAs, are part of it. This study is the first step to understand the role of csRNAs in the adaptation of S. agalactiae. This bacterium does not currently exhibit extensive antibiotic resistance. However, it is crucial to find alternatives before multidrug resistance emerges. Therefore, we propose that drugs targeting regulatory RNAs with Srn024-like activities would affect pathogens by reducing their abilities to form biofilm and to adapt to host niches.

Lactococcus lactis' Effect on the Intestinal Microbiota of Streptococcus agalactiae-Infected Zebrafish (Danio rerio)

Streptococcus agalactiae is a common pathogen in aquaculture that disrupts the balance of the intestinal microbiota and threatens fish health, causing enormous losses to the aquaculture industry. In this study, we isolated and screened a Lactococcus lactis KUST48 (LLK48) strain with antibacterial effect against S. agalactiae in vitro and used it as a potential probiotic to explore its therapeutic effect on zebrafish (Danio rerio) infected with S. agalactiae. This study divided zebrafish into 3 groups: control group, injected with phosphate-buffered saline; infection group, injected with S. agalactiae; and treatment group, treated with LLK48 after S. agalactiae injection. Then, the 16S rRNA gene sequences of the intestinal microbiota of these 3 groups were sequenced using Illumina high-throughput sequencing technology. The results showed that the relative abundance of intestinal bacteria was significantly decreased in the infection group, and a high relative abundance of S. agalactiae was observed. The relative abundance of the intestinal microbiota was increased in the treatment group, with a decrease in the relative abundance of S. agalactiae compared to that in the control group. In the Cluster of Orthologous Groups of proteins function classification, the relative abundance of each biological function in the infection group was significantly lower than that of the control and treatment groups, showing that LLK48 has a positive therapeutic effect on zebrafish infected with S. agalactiae. This study provides a foundation for exploring the pathogenic mechanism of S. agalactiae on fish and their intestinal symbionts, and also presents a new approach for the treatment of S. agalactiae infections in fish aquaculture systems. IMPORTANCE L. lactis KUST48 (LLK48) with a bacteriostatic effect against S. agalactiae was isolated from tilapia intestinal tracts. S. agalactiae infection significantly reduced the relative abundance of intestinal bacteria and various physiological functions in zebrafish intestines. LLK48 demonstrated infection and subsequent therapeutic effects on the S. agalactiae infection in the zebrafish intestine. Therefore, the potential probiotic LLK48 can be considered as a therapeutic treatment for S. agalactiae infections in aquaculture, which can reduce the use of antibiotics and help maintain fish health.

Streptococcosis a Re-Emerging Disease in Aquaculture: Significance and Phytotherapy

Simple Summary

Streptococcosis is an economical important bacterial disease that can seriously cause huge losses in the global aquaculture sector. In recent years studies have focused on to use extracts or essences of medicinal herbs and plants to control or treat the disease outbreaks and, in most cases the results were promising. The essential oils of the herbs or plants are more effective than the extracts and, the extracts examined have moderate efficacy in term of increasing fish survival against fish streptococcosis that could be due to the enhancement of fish immunity by the herb bio-compounds. The lack of dosage optimization, toxicity and bioavailability assays of a specific herb/plant or its bioactive compound in fish organs make it difficult to judge the validation of clinical efficacy of a particular herb/plant against fish streptococcosis, and thus, required further investigations.

Abstract

Streptococcosis, particularly that caused by S. iniae and S. agalactiae, is a major re-emerging bacterial disease seriously affecting the global sustainability of aquaculture development. Despite a wide spread of the disease in aquaculture, few studies have been directed at assessing the in vitro antagonistic activity and in vivo efficacy of medicinal herbs and other plants against streptococcal agents. Most in vitro studies of plant extractives against S. iniae and S. agalactiae have found antibacterial activity, but essential oils, especially those containing eugenol, carvacrol or thymol, are more effective. Although essential oils have shown better anti-streptococcal activity in in vitro assays, in vivo bioassays require more attention. The extracts examined under in vivo conditions show moderate efficacy, increasing the survival rate of infected fish, probably through the enhancement of immunity before challenge bioassays. The available data, however, lack dosage optimization, toxicity and bioavailability assays of a specific plant or its bioactive compound in fish organs; hence, it is difficult to judge the validation of clinical efficacy for the prevention or treatment of fish streptococcosis. Despite the known bioactive compounds of many tested plants, few data are available on their mode of action towards streptococcal agents. This review addresses the efficacy of medicinal plants to fish streptococcosis and discusses the current gaps.

Natural component plumbagin as a potential antibacterial agent against Streptococcus agalactiae infection

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), can infect humans, terrestrial animals and fish. The emergence of bacterial resistance of S. agalactiae to antibiotics leads to an urgent need of exploration of new antimicrobial agents. In the study, the antibacterial activity of natural component plumbagin (PLB) against S. agalactiae was investigated in vitro and in vivo. The results showed that the minimal inhibitory concentration (MIC) of PLB against S. agalactiae was 8 mg/L. The growth curve assay revealed that PLB could inhibit the growth of S. agalactiae. In addition, the time-killing curve showed that S. agalactiae was killed almost completely by 2-fold MIC of PLB within 12 h. Transmission electron microscopy results showed obvious severe morphological destruction and abnormal cells of S. agalactiae after treated with PLB. The pathogenicity of S. agalactiae to zebrafish was significantly decreased after preincubation with PLB for 2 h in vitro, further indicating the bactericidal activity of PLB. Interestingly, PLB could kill S. agalactiae without inducing resistance development. Furthermore, pretreatment and post-treatment assays suggested that PLB also exhibited the antibacterial activity against S. agalactiae infection in vivo by effectively reducing the bacterial load and improving the survival rate of S. agalactiae-infected zebrafish. In summary, PLB had potent antibacterial activity against S. agalactiae in vitro and in vivo, and it could be an excellent antimicrobial candidate to prevent and control S. agalactiae infection.

GBS-SBG - GBS Serotyping by Genome Sequencing

Group B Streptococcus (GBS; Streptococcus agalactiae) is the most common cause of neonatal meningitis and a rising cause of sepsis in adults. Recently, it has also been shown to cause foodborne disease. As with many other bacteria, the polysaccharide capsule of GBS is antigenic, enabling its use for strain serotyping. Recent advances in DNA sequencing have made sequence-based typing attractive (as has been implemented for several other bacteria, including Escherichia coli, Klebsiella pneumoniae species complex, Streptococcus pyogenes, and others). For GBS, existing WGS-based serotyping systems do not provide complete coverage of all known GBS serotypes (specifically including subtypes of serotype III), and none are simultaneously compatible with the two most common data types, raw short reads and assembled sequences. Here, we create a serotyping database (GBS-SBG, GBS Serotyping by Genome Sequencing), with associated scripts and running instructions, that can be used to call all currently described GBS serotypes, including subtypes of serotype III, using both direct short-read- and assembly-based typing. We achieved higher concordance using GBS-SBG on a previously reported data set of 790 strains. We further validated GBS-SBG on a new set of 572 strains, achieving 99.8% concordance with PCR-based molecular serotyping using either short-read- or assembly-based typing. The GBS-SBG package is publicly available and will hopefully accelerate and simplify serotyping by sequencing for GBS.

Molecular Investigation of Recurrent Streptococcus iniae Epizootics Affecting Coral Reef Fish on an Oceanic Island Suggests at Least Two Distinct Emergence Events

Streptococcus iniae is an emerging zoonotic pathogen of increasing concern for aquaculture and has caused several epizootics in reef fishes from the Caribbean, the Red Sea and the Indian Ocean. To study the population structure, introduction pathways and evolution of S. iniae over recurring epizootics on Reunion Island, we developed and validated a Multi Locus Sequence Typing (MLST) panel using genomic data obtained from 89 isolates sampled during epizootics occurring over the past 40years in Australia, Asia, the United States, Israel and Reunion Island. We selected eight housekeeping loci, which resulted in the greatest variation across the main S. iniae phylogenetic clades highlighted by the whole genomic dataset. We then applied the developed MLST to investigate the origin of S. iniae responsible for four epizootics on Reunion Island, first in inland aquaculture and then on the reefs from 1996 to 2014. Results suggest at least two independent S. iniae emergence events occurred on the island. Molecular data support that the first epizootic resulted from an introduction, with inland freshwater aquaculture facilities acting as a stepping-stone. Such an event may have been facilitated by the ecological flexibility of S. iniae, able to survive in both fresh and marine waters and the ability of the pathogen to infect multiple host species. By contrast, the second epizootic was associated with a distinct ST of cosmopolitan distribution that may have emerged as a result of environment disturbance. This novel tool will be effective at investigating recurrent epizootics occurring within a given environment or country that is despite the fact that S. iniae appears to have low genetic diversity within its lineage.

The Role of Streptococcus spp. in Bovine Mastitis

The Streptococcus genus belongs to one of the major pathogen groups inducing bovine mastitis. In the dairy industry, mastitis is the most common and costly disease. It not only negatively impacts economic profit due to milk losses and therapy costs, but it is an important animal health and welfare issue as well. This review describes a classification, reservoirs, and frequencies of the most relevant Streptococcus species inducing bovine mastitis (S. agalactiae, S. dysgalactiae and S. uberis). Host and environmental factors influencing mastitis susceptibility and infection rates will be discussed, because it has been indicated that Streptococcus herd prevalence is much higher than mastitis rates. After infection, we report the sequence of cow immune reactions and differences in virulence factors of the main Streptococcus species. Different mastitis detection techniques together with possible conventional and alternative therapies are described. The standard approach treating streptococcal mastitis is the application of ß-lactam antibiotics. In streptococci, increased antimicrobial resistance rates were identified against enrofloxacin, tetracycline, and erythromycin. At the end, control and prevention measures will be considered, including vaccination, hygiene plan, and further interventions. It is the aim of this review to estimate the contribution and to provide detailed knowledge about the role of the Streptococcus genus in bovine mastitis.

Phenotype, genotype and pathogenicity of Streptococcus agalactiae isolated from cultured tilapia (Oreochromis spp.) in Taiwan

Tilapia (Oreochromis spp.) is globally used as an aquaculture fish species due to its high growth rate and disease resistance. However, it faces an increased risk of streptococcosis. Streptococcus agalactiae, also known as group B streptococcus (GBS), is the most important tilapia pathogen in Asia. Studies of Str. agalactiae infection in Taiwan are still unclear. Thus, this study aimed to explore the phenotype, genotype and pathogenicity of Str. agalactiae isolated from cultured tilapia in Taiwan in 2016-2018. The analysis revealed that 85% of the strains displayed β-haemolysis and 15% showed γ-haemolysis, with the same capsule level, and were positive for the CAMP test. The Rapid ID 32 Strep test showed a similarity of Rapid ID 32 Strep is more than 99.5% to GBS. Genotypic distribution by molecular serotyping detected only serotype Ia from all isolates, despite the regional differences. Pulsed-field gel electrophoresis (PFGE) was categorized into 3 and 10 clusters by restriction enzymes SmaI and ApaI, respectively. Virulence genes and antimicrobial resistance genes presented the same profile in all isolates. The challenge test with 10⁶  CFU/fish (LD₅₀ ), administered intraperitoneally, showed that the β-haemolysis strains had a higher mortality rate than γ-haemolysis, although they were from the same cluster from PFGE, year and region.

Application of the FTA elute card coupled with visual colorimetric loop-mediated isothermal amplification for the rapid diagnosis of Streptococcus agalactiae in farmed tilapia (Oreochromis niloticus)

A method combining the FTA Elute card and visual colorimetric loop-mediated isothermal amplification (FTA-e/LAMP) was tested to diagnose Streptococcus agalactiae infections in vitro and in vivo. FTA-e/LAMP consists of two main steps: first, the FTA card is used to extract DNA and then a colorimetric loop-mediated isothermal amplification (LAMP) reaction is carried out on the extracted DNA. In vitro sensitivity was 1.9 x 10²  CFU/mL, and regarding specificity, all nine S. agalactiae strains tested positive. All Streptococcus spp. tested negative, except for S. dysgalactiae, thereby indicating the need for another set of primers to distinguish this species from S. agalactiae. To diagnose S. agalactiae infections using FTA-e/LAMP in vivo, two experimental trials on juvenile Oreochromis niloticus infected with bovine or piscine strains were carried out. Sensitivity in symptomatic fish was 100%, and 50.7% of fish without signs were positive. All negative control fish tested negative (n = 28). No bacteria were detected after 16 days post-infection (dpi). Accuracy during the first week (1-7 dpi) was 89% and decreased to 44% thereafter (10-22 dpi). FTA-e/LAMP results suggest that this method is a promising tool for early and fast diagnosis of S. agalactiae on tilapia farms.

Isolation and molecular detection of Streptococcus agalactiae from popped eye disease of cultured Tilapia and Vietnamese koi fishes in Bangladesh

Objective

Present research aims to isolate, identify, and determine the virulence of the Streptococcus agalactiae (group B Streptococcus; GBS), isolated from popped eye disease affected Tilapia and Vietnamese Koi (V. Koi) fishes.

Materials and Methods

A total of 330 fish samples were collected, of which Tilapia (n = 180) and V. Koi (n = 150), were collected from 35 affected ponds of four selected districts of Bangladesh. Isolation of the bacterium was done using different culture media (Nutrient broth, Plate count agar, Tryptic Soy Agar, and Blood agar), and identification by using various biochemical tests (conventional and using API 20 Strep kit) and polymerase chain reaction (PCR) using primers against 16S rRNA gene of S. agalactiae. Antibiotic susceptibility of the bacteria was performed using seven different antibiotics disc (Tetracycline, Oxytetracycline, Chlortetracycline, Streptomycin, Ciprofloxacin, Gentamicin, and Neomycin). Virulence of the isolated S. agalactiae was determined by infecting healthy Tilapia and V. Koi fishes through experimental infection.

Results

Isolated bacteria were found Gram-positive paired and chained cocci, β-hemolytic and non-motile. Findings of biochemical and serological tests indicate that the isolated bacterium belongs to Group B Streptococcus of Lancefield classification. PCR result also confirmed that the bacteria were S. agalactiae. The bacterial isolates possessed resistance property against all the seven antibiotics used in this study. The isolated GBS was found highly virulent and showed 80%–90% mortality for Tilapia and V. Koi fishes in experimental infection within 1–6 days of post-infection.

Conclusion

From the findings of this study, it may be concluded that isolated GBS from the Tilapia and V. Koi fishes were highly virulent and possessed multidrug-resistance properties.

Streptococcal Infections in Marine Mammals

Marine mammals are sentinels for the marine ecosystem and threatened by numerous factors including infectious diseases. One of the most frequently isolated bacteria are beta-hemolytic streptococci. However, knowledge on ecology and epidemiology of streptococcal species in marine mammals is very limited. This review summarizes published reports on streptococcal species, which have been detected in marine mammals. Furthermore, we discuss streptococcal transmission between and adaptation to their marine mammalian hosts. We conclude that streptococci colonize and/or infect marine mammals very frequently, but in many cases, streptococci isolated from marine mammals have not been further identified. How these bacteria disseminate and adapt to their specific niches can only be speculated due to the lack of respective research. Considering the relevance of pathogenic streptococci for marine mammals as part of the marine ecosystem, it seems that they have been neglected and should receive scientific interest in the future.

Response of chemokine receptors CXCR2 and integrin β2 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain of Nile tilapia Oreochromis niloticus

CXCR2 is a G-protein-coupled cell surface chemokine receptor, and integrins are heterodimeric transmembrane (TM) glycoproteins. These proteins work together to activate neutrophils in the immune defense, but knowledge of their function in tilapia is limited. RACE technology was used to clone the full length of the Nile tilapia Oreochromis niloticus Cxcr2 gene, which included a 954 bp open reading frame encoding 318 amino acids, and the integrin β2 gene, with a 2373 bp open reading frame and 791 amino acids. Sequence analyses showed that Cxcr2 and integrin β2 are conserved among species. Expression profile was performed using qRT-PCR and indicated that Cxcr2 and integrin β2 were distributed throughout the examined organ tissues, with highest expression observed in the immune tissues. Expression of Cxcr2 and integrin β2 were increased after challenged with Streptococcus agalactiae or Aeromonas hydrophila. Results suggest that Cxcr2 and integrin β2 genes play a role in immune response in Nile tilapia and provide basic data for molecular-assistant selection of disease-resistant bloodstock to improve the production.

Intracoelomic- and Intramuscular-Injection Challenge Model of Piscine Streptococcosis in White Sturgeon Fingerlings

Streptococcus iniae is a zoonotic pathogen and one of the major aetiologic agents of streptococcosis. In White Sturgeon Acipenser transmontanus, S. iniae infection typically presents as a necrotizing and heterophilic myositis, causing 30-50% mortality in infected fish. To gain a better understanding of the pathogenesis of streptococcosis in White Sturgeon, and to identify the experimental route of infection that most closely mimics the natural disease, fingerlings were challenged with a single dose of 1.3 × 10⁸  cells/fish of S. iniae that was administered via intracoelomic/intraperitoneal (IC) or intramuscular (IM) routes. Acute mortalities were present only in the IM-challenged fish, with first mortality occurring 4 d postchallenge and the mortality rate reaching 18.3% after 9 d. The challenged fish presented erratic swimming, ulcerative skin lesions, and hemorrhages in the liver and swim bladder. Streptococcus iniae was recovered from the kidney and brain tissues of moribund and dead fish. Histopathologic analysis of fish that died acutely revealed massive proliferation of bacteria in the muscle at the injection site and within vascular organs such as the heart and spleen, with variable amounts of tissue necrosis including a necrotizing myositis. Fish that died closer to 9 d postchallenge demonstrated more pronounced multifocal to locally extensive granulomatous inflammation of skeletal muscle at the injection site, liver, kidney, and spleen. No mortality, clinical signs, or gross changes were observed in the control or IC-challenged fish. Postmortem evaluation of 10 survivors in each treatment was performed to determine carrier status in the brain and posterior kidney tissues. The prevalence of S. iniae in survivors was 10% and 0% in the IM- and IC-challenged groups, respectively. The results from this study suggest that IM-injection challenge methods are suitable for inducing streptococcosis in White Sturgeon, and they may be the preferred method for studying the pathogenesis of the naturally occurring disease in this species.

Single molecule real-time sequencing and RNA-seq unravel the role of long non-coding and circular RNA in the regulatory network during Nile tilapia (Oreochromis niloticus) infection with Streptococcus agalactiae

BACKGROUND

The tilapia aquaculture industry is facing heavy economic losses due to Streptococcus agalactiae (S. agalactiae) infections. While progress has been made in past years, the lack of a high-quality tilapia genome and transcript annotations makes systematic and comprehensive exploration for a non-coding RNA regulatory network associated with the infection process unfeasible, and it stunts further research focused on disease defense and treatment. Herein, single molecular real time sequencing (SMRT-Seq) and RNA-seq data were utilized to generate a high-quality transcript annotation. In addition, Changes in mRNA and non-coding RNA expression were also analyzed during a S. agalactiae infection in tilapia.

FINDINGS

In total, 16.79 Gb of clean data were obtained by sequencing on six SMRT cells, with 712,294 inserts (326,645 full-length non-chimeric reads and 354,188 non-full-length reads). A total of 197,952 consensus transcripts were obtained. Additionally, 55,857 transcript sequences were acquired, with 12,297 previously annotated and 43,560 newly identified transcripts. To further examine the immune response in Oreochromis niloticus following a S. agalactiae infection, a total of 470.62 Gb of clean data was generated by sequencing a library containing 18 S. agalactiae infected tilapia samples. Of the identified genes, 9911 were newly exploited, of which 7102 were functional annotated. Furthermore, 7874 mRNAs, 1281 long non-coding RNAs (out of 21,860 long non-coding RNAs), and 61 circular RNAs (out of 1026 circular RNAs) were found to be differentially expressed during infection, with the 1026 circRNAs not previously identified in tilapia. Moreover, k-means clustering and WGCNA analyses revealed that the immune response of tilapia to a S. agalactiae infection can be divided into three stages: cytokines driven rapid immune response, energy metabolism promotion, and the production of lysosomes and phagosomes. During this response, the head kidney and spleen have synergistic effects, while maintaining independent characteristics. Finally, lncRNA-mRNA (trans and cis), lncRNA-miRNA-mRNA, and circRNA-miRNA-mRNA regulatory networks were constructed and revealed that non-coding RNA is involved in the regulation of immune-related genes.

CONCLUSIONS

This study generated a greatly-improved transcript annotation for tilapia using long-read PacBio sequencing technology, and revealed the presence of a regulatory network comprised of non-coding RNAs in Nile tilapia infected with S. agalactiae.

In silico Prediction of New Drug Candidates Against the Multidrug-Resistant and Potentially Zoonotic Fish Pathogen Serotype III Streptococcus agalactiae

Streptococcus agalactiae is an invasive multi-host pathogen that causes invasive diseases mainly in newborns, elderly, and individuals with underlying health complications. In fish, S. agalactiae causes streptococcosis, which is characterized by septicemia and neurological signs, and leads to great economic losses to the fish farming industry worldwide. These bacteria can be classified into different serotypes based on capsular antigens, and into different sequence types (ST) based on multilocus sequence typing (MLST). In 2015, serotype III ST283 was identified to be associated with a foodborne invasive disease in non-pregnant immunocompetent humans in Singapore, and the infection was related to raw fish consumption. In addition, a serotype III strain isolated from tilapia in Brazil has been reported to be resistant to five antibiotic classes. This specific serotype can serve as a reservoir of resistance genes and pose a serious threat to public health. Thus, new approaches for the control and treatment of S. agalactiae infections are needed. In the present study, 24 S. agalactiae serotype III complete genomes, isolated from human and fish hosts, were compared. The core genome was identified, and, using bioinformatics tools and subtractive criteria, five proteins were identified as potential drug targets. Furthermore, 5,008 drug-like natural compounds were virtually screened against the identified targets. The ligands with the best binding properties are suggested for further in vitro and in vivo analysis.

Genome-Wide DNA Methylation and RNA Analysis Reveal Potential Mechanism of Resistance to Streptococcus agalactiae in GIFT Strain of Nile Tilapia (Oreochromis niloticus )

Streptococcus agalactiae is an important pathogenic bacterium causing great economic loss in Nile tilapia (Oreochromis niloticus) culture. Resistant and susceptible groups sharing the same genome showed significantly different resistance to S. agalactiae in the genetically improved farmed tilapia strain of Nile tilapia. The resistance mechanism is unclear. We determined genome-wide DNA methylation profiles in spleen of resistant and susceptible O. niloticus at 5 h postinfection with S. agalactiae using whole-genome bisulfite sequencing. The methylation status was higher in the spleen samples from resistant fish than in the susceptible group. A total of 10,177 differentially methylated regions were identified in the two groups, including 3725 differentially methylated genes (DMGs) (3129 hyper-DMGs and 596 hypo-DMGs). The RNA sequencing showed 2374 differentially expressed genes (DEGs), including 1483 upregulated and 891 downregulated. Integrated analysis showed 337 overlapping DEGs and DMGs and 82 overlapping DEGs and differentially methylated region promoters. By integrating promoter DNA methylation with gene expression, we revealed four immune-related genes (Arnt2, Nhr38, Pcdh10, and Ccdc158) as key factors in epigenetic mechanisms contributing to pathogen resistance. Our study provided systematic methylome maps to explore the epigenetic mechanism and reveal the methylation loci of pathogen resistance and identified methylation-regulated genes that are potentially involved in defense against pathogens.

Gangrenous mastitis in dromedary camels in UAE caused by Streptococcus agalactiae

BACKGROUND

Mastitis is a disease of economic concern that affects dairy industry worldwide. This study aimed to investigate and identify possible etiologies encountered in an episode of acute gangrenous mastitis in lactating she-camels in Al Dhafra region, Abu Dhabi Emirate, United Arab Emirates (UAE). Beside the routine clinical examination, conventional bacteriological methods were used to isolate and identify possible aerobic/anaerobic bacterial or fungal pathogens from cultured milk samples collected from the mastitic she-camels. Moreover, quantitative real-time polymerase chain reaction (qPCR) was used for the detection of Mycoplasma agalactiae and Mycoplasma bovis strains, and the 16S rRNA gene was sequenced to confirm the isolation. The isolates were also tested for their susceptibility to antimicrobials.

RESULTS

Acute gangrenous mastitis is reported in the dromedary camel herd with about 80% morbidity rate among lactating she-camels exhibited acute, painful hard swelling of affected teat, quarter or entire udder. About 41.7% of the infected animals were stamped out for culling due to complete or partial amputation of udder quarters. Streptococcus agalactiae was the sole isolated organism (6 isolates). The antimicrobial susceptibility testing revealed that, the Streptococcus agalactiae isolates were sensitive to both penicillin and ampicillin. Comparison of the 16S rRNA gene sequencing results by BLASTN confirmed the presence of Streptococcus agalactiae with high confidence (100% identity). Phylogenetic analysis indicated clustering of one isolate (CMAUAE accession number; MN267805.1) with Streptococcus agalactiae that infects multi-hosts including humans, while strains (CMBUAE to CMFUAE with accession numbers; MN267806.1 to MN267810.1 respectively) clustered with Streptococcus agalactiae that infects humans. No Mycoplasma spp was detected by qPCR analysis.

CONCLUSIONS

In the present study, the Streptococcus agalactiae was found to be the main cause of acute gangrenous mastitis in dromedary camels in UAE. More research should be done to investigate other possible causes of clinical or subclinical mastitis in dromedary camels in UAE.

Mechanisms and the role of probiotic Bacillus in mitigating fish pathogens in aquaculture

Diseases are natural components of the environment, and many have economic implications for aquaculture and fisheries. Aquaculture is a fast-growing industry with the aim to meet the high protein demand of the ever-increasing global population; however, the emergence of diseases is a major setback to the industry. Probiotics emerged as a better solution to curb the disease problem in aquaculture among many alternatives. Probiotic Bacillus has been proven to better combat a wide range of fish pathogens relative to other probiotics in aquaculture; therefore, understanding the various mechanisms used by Bacillus in combating diseases will help improve their mode of action hence yielding better results in their combat against pathogens in the aquaculture industry. Thus, an overview of the mechanisms (production of bacteriocins, suppression of virulence gene expression, competition for adhesion sites, production of lytic enzymes, production of antibiotics, immunostimulation, competition for nutrients and energy, and production of organic acids) used by Bacillus probiotics in mitigating fish pathogens ranging from Aeromonas, Vibrio, Streptococcus, Yersinia, Pseudomonas, Clostridium, Acinetobacter, Edwardsiella, Flavobacterium, white spot syndrome virus, and infectious hypodermal and hematopoietic necrosis virus proven to be mitigated by Bacillus have been provided.

Large-scale profiling of the proteome and dual transcriptome in Nile tilapia (Oreochromis niloticus) challenged with low- and high-virulence strains of Streptococcus agalactiae

Streptococcus agalactiae is a common pathogen in aquatic animals, especially tilapia, that hinders aquaculture development and leads to serious economic losses. Previously, a S. agalactiae strain named HN016 was identified from infected tilapia, and the attenuated strain YM001 was subsequently obtained by continuous passaging in Tryptic Soy Broth (TSB) medium. YM001 has been demonstrated as a safe vaccine for S. agalactiae infection in tilapia. To understand the molecular bases of the virulence of these two strains, we performed proteomic and transcriptomic analysis to reveal the protein and gene expression changes in the liver and intestine during the infection process. HN016 significantly decreased the contents of white blood cells (WBCs), neutrophils (NEUs), red blood cells (RBCs) and hematocrit (HCT) and increased the levels of total protein (TP), albumin (ALB) and globulin (GLO), while no such significant differences were observed when comparing the control with YM001. During the infection process, pathogenic peptidoglycan hydrolase, CSPA and membrane proteins were significantly differentially expressed between YM001 and HN016. Furthermore, both proteome and transcriptome data showed that the complement and coagulation cascades pathway and the antigen processing and presentation pathway were stimulated in the liver and intestine, respectively, by YM001 infection compared to HN016 infection. The interaction network analysis of key virulence genes from pathogens suggested that CSPA, as a key node, affects the expression of DOLPP1, MIPEP, PA2G4, OCIAD1, G3BP1 and CLIC5 with a positive correlation. The present evidence suggests that during the infection process, CSPA was the key genes contributing to low virulence in YM001.

Galleria mellonella as an infection model for the multi-host pathogen Streptococcus agalactiae reflects hypervirulence of strains associated with human invasive disease

Streptococcus agalactiae, or group B Streptococcus (GBS), infects diverse hosts including humans and economically important species such as cattle and fishes. In the context of human health, GBS is a major cause of neonatal infections and an emerging cause of invasive disease in adults and of foodborne disease in Southeast Asia. Here we show that GBS is able to establish a systemic infection in Galleria mellonella larvae that is associated with extensive bacterial replication and dose-dependent larval survival. This infection model is suitable for use with GBS isolates from both homeothermic and poikilothermic hosts. Hypervirulent sequence types (ST) associated with invasive human disease in neonates (ST17) or adults (ST283) show increased virulence in this model, indicating it may be useful in studying GBS virulence determinants, albeit with limitations for some host-specific virulence factors. In addition, we demonstrate that larval survival can be afforded by antibiotic treatment and so the model may also be useful in the development of novel anti-GBS strategies. The use of G. mellonella in GBS research has the potential to provide a low-cost infection model that could reduce the number of vertebrates used in the study of GBS infection.

Multiomics analyses reveal that NOD-like signaling pathway plays an important role against Streptococcus agalactiae in the spleen of tilapia

Streptococcus aglactiae(GBS) infection in tilapia is a serious global disease that causes significant production loss. Here, we studied the role of GBS in the spleen and the spleen's response against the pathogen through dual RNA-seq and proteome technology. Animals were divided into three groups: control, virulent treated (HN016), and attenuated treated (YM001). Spleen samples were collected and analysis when a disease outbreak. Dual RNA-seq result showed the virulence factor genes of GBS, included CAMP factor, PGK, OCT, enolase, scpB, Sip, bca, were upregulation. downregulation of GapA, cylE, OCT, scpB, C5AP, rlmB, hly, FBP, in HN016 and YM001. But for proteomic, OCT and bca were downregulation, the others were upregulation. For host transcriptome KEGG analysis showed, the NOD-like receptor signaling pathway (NLRs) and TOLL-like receptor signaling pathway (TLRs) were upreguoation in HN016 infected fish than the control fish; But for proteome KEGG, only the NLRS was up, the TLRS was not change. Compared with YM001 infected fishes, for transcriptome, NLRs and TLRs in infected HN016 fishes were significance rise (p < 0.01); for proteome, the NLRs was up (p < 0.05), but TLRs was no change.Analysis of pathogen-host interaction showed that the peptidoglycan (PNG), CD2, LCK, and host's Zap70 were involved in the regulation of NLRs; PNG, LCK, and ZAP70 were involved in the regulation of TRLs. Conclusion: the virulent strain HN016 and attenuated strainYM001 differed in the quantity of virulence factors. In tilapia's innate immune system, NLRs was the main defense factors, but bacteria avoided the host defense through TLRs.

Interactions of head-kidney leucocytes from giant grouper, Epinephelus lanceolatus, with pathogenic Streptococcus agalactiae strains from marine and terrestrial origins

Streptococcus agalactiae (Group B Streptococcus, GBS) is emerging as a genetically diverse species infecting farmed and wild fish, including commercially and culturally important groupers. To better understand how S. agalactiae are pathogenic in fish, we investigated interactions between isolates from fish and terrestrial hosts and the cellular immune system of Queensland grouper Epinephelus lanceolatus using flow cytometry. Adherent head-kidney leucocytes (HKL) from Queensland grouper displayed two main cell populations with distinct forward and side scatter by flow cytometry. The population of smaller and less complex cells (P1) was composed of monocytes, lymphocytes and thrombocytes, while the population of primarily larger and more complex cells (P2) comprised predominantly of macrophages and neutrophils. The cells in P2 had higher phagocytic index and capacity when incubated with fluorescent latex beads. HKL were activated by phorbol myristate acetate (PMA) but were unresponsive to lipopolysaccharide (LPS) and peptidoglycan (PTG), suggesting the absence of specific receptors on the surface of these cells for these ligands or a requirement for intermediates. In in vitro phagocytosis assays, all fish isolates of GBS activated a respiratory burst in P2 indicated by significant production of intracellular reactive oxygen species (ROS). Similarly, dog and cat isolates of different serotype and sequence type also induced ROS production in grouper HKL. However, human, crocodile and bovine isolates of GBS did not elicit significant ROS in HKL although they coincided with the highest phagocytic index. This suggests that these strains are capable of quenching ROS production. Terrestrial isolates significantly increased mortality of Queensland grouper leucocytes in vitro, aligned with a more diverse repertoire of cellular toxins in these strains. Opsonisation of a marine strain and terrestrial strain of GBS with antiserum raised against the marine strain resulted in an increase in ROS production by HKL in both cases although there was low antigenic cross reactivity between the two strains by flow cytometry, reflecting their diverse serotypes (Ib vs III). However, pre-incubation of either strain with normal serum from grouper also increased ROS production of HKL suggesting other opsonins may be involved. Based on these results it appears that piscine and terrestrial GBS isolates have contrasting strategies when interacting with the cellular immune system of Queensland grouper; the former seemingly evading phagocytosis, whilst the latter are readily phagocytosed but counteract ROS production.

Genomic Insights Into the Distribution and Evolution of Group B Streptococcus

Streptococcus agalactiae, also known as Group B Streptococcus (GBS), is a bacteria with truly protean biology. It infects a variety of hosts, among which the most commonly studied are humans, cattle, and fish. GBS holds a singular position in the history of bacterial genomics, as it was the substrate used to describe one of the first major conceptual advances of comparative genomics, the idea of the pan-genome. In this review, I describe a brief history of GBS and the major contributions of genomics to understanding its genome plasticity and evolution as well as its molecular epidemiology, focusing on the three hosts mentioned above. I also discuss one of the major recent paradigm shifts in our understanding of GBS evolution and disease burden: foodborne GBS can cause invasive infections in humans.

Spatiotemporal distribution of Streptococcus agalactiae attenuated vaccine strain YM001 in the intestinal tract of tilapia and its effect on mucosal associated immune cells

In this study, the tilapia was orally vaccinated by the attenuated Streptococcus agalactiae(S. agalactiae) strain YM001, and the distribution and the pathological effect of strain YM001 in different intestinal segments of tilapia were evaluated by real-time PCR(qPCR), immunohistochemistry(IHC) and histomorphology. The qPCR results showed that the number of bacteria was the highest in the intestinal tracts at 12 h post oral gavage in the YM001 group, then began to decrease sharply and eliminated at 7 d. And the number of bacteria was highest in the foregut, hindgut, and rectum at 12 h, 24 h, and 3 d, respectively. IHC indicated that bacteria mainly distributed in the margin epithelium and the goblet cells at 12 h - 24 h, and in the submucosa and muscle layer in the YM001 group in 3 d post gavage, then almost disappeared at 7 d. Histological examination of intestines post gavage displayed that an inflammation was observed at 7 d in the YM001 group and the intestinal structure was fully recovered at 15 d. and the intestinal structure was fully recovered at 15 d. Conclusion: The attenuated S. agalactiae vaccine strain YM001 could enter the intestinal tissue after oral gavage and had a strong spatial and temporal selectivity in the intestinal tract, which could cause obvious mucosal immune response and mild pathological reaction, but the pathological change could be gradually repaired with the extinction of bacteria in the body.

Characterization and expression of galectin-3 after Streptococcus agalactiae and Aeromonas hydrophila challenge in GIFT strain Nile tilapia (Oreochromis niloticus)

In mammals, Galectin-3 has been revealed to be widely expressed in immune cells and played important role in immune reactions. However, Galectin-3 is frequently less reported in teleost. In the present study, a molecular characterization and expression analysis of galectin-3 were conducted in GIFT strain Nile tilapia. The full-length cDNA is 1034 bp with 690 bp of protein coding sequences. The result of qRT-PCR showed that the mRNA of galectin-3 was widely expressed in various tissues (heart, liver, spleen, gill, kidney, brain, intestine, skin, muscle, and ovary), and the higher expression was observed in immune-related tissues (liver and spleen). The time-course expression analysis revealed that galectin-3 was significantly up-regulated in intestine (5 h, 50 h, and 7 d), liver (5 h, 50 h, and 7 d), spleen (5 and 50 h), head-kidney (5 and 50 h), gill (5 h and 7 d) after Streptococcus agalactiae challenge, and significantly up-regulated in intestine (18, 24, 36, 72, and 96 h), liver (6, 18, 24, 96 h, and 6 d), spleen (18, 24, 36, 72, and 96 h), head-kidney (6, 12, 18, 24, 36, 72, and 96 h), and gill (12, 18, 24, and 36 h) after Aeromonas hydrophila challenge. Taken together, these data suggest that galectin-3 plays a role in immune responses in Nile tilapia after bacterial challenge.

Oral vaccination of tilapia against Streptococcus agalactiae using Bacillus subtilis spores expressing Sip

Streptococcus agalactiae infections are becoming an increasing problem in aquaculture because of significant morbidity and mortality, which restricts the healthy development of tilapia aquaculture. To seek safe and effective prevention measures, a Bacillus subtilis GC5 surface displayed vaccine was prepared and applied orally in tilapia. The study first showed that recombinant spores can engraft in the tilapia intestine. Then, the effect of protection and the immune responses were evaluated. The results of ELISA showed that Sip-specific antibody in the sera of GC5-Sip-immunized fish can be detected after the first oral administration when compared to the phosphate buffer saline (PBS) control group, and the levels of specific IgM gradually strengthened with boosting, so does the specific antibody against bacteria, proving that humoral immunity was induced. Quantitative real-time PCR (qRT-PCR) results showed that the immune-related gene expression of the gut and spleen exhibited a different rising trend in the GC5-Sip group, revealing that innate immune response and local as well as systemic cellular immunity were induced. The outcome of fish immunized with GC5-Sip spores provided a relative percent survival (RPS) of 41.7% against S. agalactiae and GC5 group had an RPS of 24.2%, indicating that GC5-Sip was safe and effective in protecting tilapia against bacterial infection. Our study demonstrated that the oral administration of B. subtilis spores expressing Sip could cause an effective immune response and offer good resistance to bacterial infection. Our work may lead to the development of new ideas for immunoprophylaxis against S. agalactiae infection.

Delineation of the pan-proteome of fish-pathogenic Streptococcus agalactiae strains using a label-free shotgun approach

BACKGROUND

Streptococcus agalactiae (GBS) is a major pathogen of Nile tilapia, a global commodity of the aquaculture sector. The aims of this study were to evaluate protein expression in the main genotypes of GBS isolated from diseased fishes in Brazil using a label-free shotgun nano-liquid chromatography-ultra definition mass spectrometry (nanoLC-UDMS^E) approach and to compare the differential abundance of proteins identified in strains isolated from GBS-infected fishes and humans.

RESULTS

A total of 1070 protein clusters were identified by nanoLC-UDMS^E in 5 fish-adapted GBS strains belonging to sequence types ST-260 and ST-927 and the non-typeable (NT) lineage and 1 human GBS strain (ST-23). A total of 1065 protein clusters corresponded to the pan-proteome of fish-adapted GBS strains; 989 of these were identified in all fish-adapted GBS strains (core proteome), and 62 were shared by at least two strains (accessory proteome). Proteins involved in the stress response and in the regulation of gene expression, metabolism and virulence were detected, reflecting the adaptive ability of fish-adapted GBS strains in response to stressor factors that affect bacterial survival in the aquatic environment and bacterial survival and multiplication inside the host cell. Measurement of protein abundance among different hosts showed that 5 and 26 proteins were exclusively found in the human- and fish-adapted GBS strains, respectively; the proteins exclusively identified in fish isolates were mainly related to virulence factors. Furthermore, 215 and 269 proteins were up- and down-regulated, respectively, in the fish-adapted GBS strains in comparison to the human isolate.

CONCLUSIONS

Our study showed that the core proteome of fish-adapted GBS strains is conserved and demonstrated high similarity of the proteins expressed by fish-adapted strains to the proteome of the human GBS strain. This high degree of proteome conservation of different STs suggests that, a monovalent vaccine may be effective against these variants.

The complement component 1 q (C1q) in Nile tilapia (Oreochromis niloticus): Functional characterization in host defense against bacterial infection and effect on cytokine response in macrophages

Complement component 1q (C1q) is the initial protein of the classical complement pathway and plays an important role in immune response against bacterial infection. In this study, the full-length of C1q subcomponent A, B and C chain genes (C1qA, C1qB and C1qC) were identified and characterized from Nile tilapia (Oreochromis niloticus). Molecular characterization of these three C1q subcomponents (OnC1qs) harbored conserved amino acids through analyses of multiple sequence alignment and phylogenetic tree, which were homologous to other teleost species. Expression analysis revealed that the OnC1qs were highly expressed in liver. After the in vivo challenges of Streptococcus agalactiae and LPS, the mRNA expressions of OnC1qs were significantly up-regulated in liver. Meanwhile, the concentration variation of OnC1qs at the protein level from tilapia serum after challenge with S. agalactiae were measured by a competitive-inhibition ELISA. In addition, the up-regulation expressions of OnC1qs were also demonstrated in head kidney adherent leukocytes and the cell culture medium in vitro stimulation with S. agalactiae, Aeromonas hydrophila and LPS, respectively. Moreover, the recombinant OnC1qs enhanced expression of cytokines IL-6, IL-8 and IL-10 in head kidney adherent leukocytes, and were able to bind both heat-aggregated mouse IgG and IgM. Taken together, the results of this study indicated that OnC1qs might be involved in host defense against bacterial infection in Nile tilapia.

Current Challenges of Streptococcus Infection and Effective Molecular, Cellular, and Environmental Control Methods in Aquaculture

Several bacterial etiological agents of streptococcal disease have been associated with fish mortality and serious global economic loss. Bacterial identification based on biochemical, molecular, and phenotypic methods has been routinely used, along with assessment of morphological analyses. Among these, the molecular method of 16S rRNA sequencing is reliable, but presently, advanced genomics are preferred over other traditional identification methodologies. This review highlights the geographical variation in strains, their relatedness, as well as the complexity of diagnosis, pathogenesis, and various control methods of streptococcal infections. Several limitations, from diagnosis to control, have been reported, which make prevention and containment of streptococcal disease difficult. In this review, we discuss the challenges in diagnosis, pathogenesis, and control methods and suggest appropriate molecular (comparative genomics), cellular, and environmental solutions from among the best available possibilities.

Basal polarization of the immune responses to Streptococcus agalactiae susceptible and resistant tilapia (Oreochromis niloticus)

One of the highest priority areas for improvement is the development of effective strategies for decreasing disease mortality levels in aquaculture production, a better understanding of the components of the fish immune system and their functions in the context of pathogen invasion is needed. Tilapia is the most common fish in South China, and Streptococcus agalactiae has become the most serious disease problem for tilapia industry in China. Here, we profiled gene expression differences between tilapia differing in their susceptibility to S. agalactiae both basally (before infection) and at three early timepoints post-infection (5 h, 50 h, and 7 d). Between group comparisons revealed 5756 unique genes differentially expressed greater than 2-fold at one or more timepoints. And the resistant fish showed much more strong ability in pathogen recognition, antigen presentation, immune activation, while the susceptible fish showed fast activation of apoptosis. Taken together, the immune profiles expand our knowledge for molecular mechanisms for disease resistance, as well as provide solid molecular resources for further identification of the candidate markers for disease-resistant selection and evaluation of disease prevention and treatment options for tilapia industry.

High Incidence of Pathogenic Streptococcus agalactiae ST485 Strain in Pregnant/Puerperal Women and Isolation of Hyper-Virulent Human CC67 Strain

Group B streptococcus (GBS) is the major pathogen causing diseases in neonates, pregnant/puerperal women, cows and fish. Recent studies have shown that GBS may be infectious across hosts and some fish GBS strain might originate from human. The purpose of this study is to investigate the genetic relationship of CC103 strains that recently emerged in cows and humans, and explore the pathogenicity of clinical GBS isolates from human to tilapia. Ninety-two pathogenic GBS isolates were identified from 19 patients with different diseases and their evolution and pathogenicity to tilapia were analyzed. The multilocus sequence typing revealed that clonal complex (CC) 103 strain was isolated from 21.74% (20/92) of patients and ST485 strain was from 14.13% (13/92) patients with multiple diseases including neonates. Genomic evolution analysis showed that both bovine and human CC103 strains alternately form independent evolutionary branches. Three CC67 isolates carried gbs2018-C gene and formed one evolutionary branch with ST61 and ST67 strains that specifically infect dairy cows. Studies of interspecies transmission to tilapia found that 21/92 (22.83%) isolates including all ST23 isolates were highly pathogenic to tilapia and demonstrated that streptococci could break through the blood-brain barrier into brain tissue. In conclusions, CC103 strains are highly prevalent among pathogenic GBS from humans and have evolved into the highly pathogenic ST485 strains specifically infecting humans. The CC67 strains isolated from cows are able to infect humans through evolutionary events of acquiring CC17-specific type C gbs2018 gene and others. Human-derived ST23 pathogenic GBS strains are highly pathogenic to tilapia.

Molecular characterization and virulence gene profiling of pathogenic Streptococcus agalactiae populations from tilapia ( Oreochromis sp.) farms in Thailand

Streptococcus spp. were recovered from diseased tilapia in Thailand during 2009-2010 ( n = 33), and were also continually collected from environmental samples (sediment and water) from tilapia farms for 9 months in 2011 ( n = 25). The relative percent recovery of streptococci from environmental samples was 13-67%. All streptococcal isolates were identified as S. agalactiae (group B streptococci [GBS]) by a species-specific polymerase chain reaction. In molecular characterization assays, 4 genotypic categories comprised of 1) molecular serotypes, 2) the infB allele, 3) virulence gene profiling patterns ( cylE, hylB, scpB, lmb, cspA, dltA, fbsA, fbsB, bibA, gap, and pili backbone-encoded genes), and 4) randomly amplified polymorphic DNA (RAPD) fingerprinting patterns, were used to describe the genotypic diversity of the GBS isolates. There was only 1 isolate identified as molecular serotype III, while the others were serotype Ia. Most GBS serotype Ia isolates had an identical infB allele and virulence gene profiling patterns, but a large diversity was established by RAPD analysis with diversity tending to be geographically dependent. Experimental infection of Nile tilapia ( Oreochromis niloticus) revealed that the GBS serotype III isolate was nonpathogenic in the fish, while all 5 serotype Ia isolates (3 fish and 2 environmental isolates) were pathogenic, with a median lethal dose of 6.25-7.56 log₁₀ colony-forming units. In conclusion, GBS isolates from tilapia farms in Thailand showed a large genetic diversity, which was associated with the geographical origins of the bacteria.

Effectivity of oral recombinant DNA vaccine against Streptococcus agalactiae in Nile tilapia

The effects of oral vaccination by two immune routes (gavage and mixed fodder administration) using a recombinant DNA vaccine SL7207-pVAX1-sip against Streptococcus agalactiae were assessed. SL7207-pVAX1-sip significantly enhanced various innate immune responses of tilapia, such as total serum protein, superoxide dismutase activity, lysozyme activity, complement C3 concentration in serum, serum antibacterial activity, and interleukin 1β and tumor necrosis factor-α. Vaccinated fish had higher relative percent survival values (57% and 63% for gavage group and mix fodder administration, respectively) at 10 weeks after S. agalactiae infection. When administered mixed fodder, the DNA vaccine SL7207-pVAX1-sip against S. agalactiae may produce more effective protection. These findings can promote the application and development of DNA vaccines in aquaculture.

Population structure and virulence gene profiles of Streptococcus agalactiae collected from different hosts worldwide

Streptococcus agalactiae is a leading cause of morbidity and mortality among neonates and causes severe infections in pregnant women and nonpregnant predisposed adults, in addition to various animal species worldwide. Still, information on the population structure of S. agalactiae and the geographical distribution of different clones is limited. Further data are urgently needed to identify particularly successful clones and obtain insights into possible routes of transmission within one host species and across species borders. We aimed to determine the population structure and virulence gene profiles of S. agalactiae strains from a diverse set of sources and geographical origins. To this end, 373 S. agalactiae isolates obtained from humans and animals from five different continents were typed by DNA microarray profiling. A total of 242 different S. agalactiae strains were identified and further analyzed. Particularly successful clonal lineages, hybridization patterns, and strains were identified that were spread across different continents and/or were present in more than one host species. In particular, several strains were detected in both humans and cattle, and several canine strains were also detected in samples from human, bovine, and porcine hosts. The findings of our study suggest that although S. agalactiae is well adapted to various hosts including humans, cattle, dogs, rodents, and fish, interspecies transmission is possible and occurs between humans and cows, dogs, and rabbits. The virulence and resistance gene profiles presented enable new insights into interspecies transmission and make a crucial contribution to the identification of suitable targets for therapeutic agents and vaccines.

Molecular and virulence characterization of highly prevalent Streptococcus agalactiae circulated in bovine dairy herds

Bovine mastitis caused by Streptococcus agalactiae continues to be one of the major veterinary and economic issues in certain areas of the world. The more prevalent S. agalactiae strains that cause bovine mastitis in China dairy farms belong to a number of bovine-adapted sequence types (STs) ST67, ST103 and ST568. However, it is unknown why these STs can emerge as highly prevalent clones in bovine dairy farms. Here, to determine if a variety of virulence characteristics were associated with these highly prevalent STs, the molecular and virulence characterization of 116 strains isolated from bovine, human, fish and environment were analyzed. Our data showed that all bovine-adapted strains could be assigned to capsular genotype Ia or II, and carried pilus island 2b, and lactose operon. Importantly, we demonstrated that the growth ability in milk, biofilm formation ability and adhesion ability to bovine mammary epithelial cells (BMECs) were significantly higher for all bovine-adapted strains compared to strains from other origins. Additionally, ST103 and ST568 strains exhibited significantly higher hemolytic activity and cytotoxicity than ST67 strains. In conclusion, our study provides substantial evidence for the hypothesis that the virulence characteristics including efficient growth in milk, elevated biofilm formation ability, together with strong adhesion ability might have favored the high prevalence of the STs in the bovine environment, whereas the hemolytic activity and cytotoxicity were not the crucial characteristics.

Pathogenicity of Human ST23 Streptococcus agalactiae to Fish and Genomic Comparison of Pathogenic and Non-pathogenic Isolates

Streptococcus agalactiae, or Group B Streptococcus (GBS), is a major pathogen causing neonatal sepsis and meningitis, bovine mastitis, and fish meningoencephalitis. CC23, including its namesake ST23, is not only the predominant GBS strain derived from human and cattle, but also can infect a variety of homeothermic and poikilothermic species. However, it has never been characterized in fish. This study aimed to determine the pathogenicity of ST23 GBS to fish and explore the mechanisms causing the difference in the pathogenicity of ST23 GBS based on the genome analysis. Infection of tilapia with 10 human-derived ST23 GBS isolates caused tissue damage and the distribution of pathogens within tissues. The mortality rate of infection was ranged from 76 to 100%, and it was shown that the mortality rate caused by only three human isolates had statistically significant difference compared with fish-derived ST7 strain (P < 0.05), whereas the mortality caused by other seven human isolates did not show significant difference compared with fish-derived ST7 strain. The genome comparison and prophage analysis showed that the major genome difference between virulent and non-virulent ST23 GBS was attributed to the different prophage sequences. The prophage in the P1 region contained about 43% GC and encoded 28–39 proteins, which can mediate the acquisition of YafQ/DinJ structure for GBS by phage recombination. YafQ/DinJ belongs to one of the bacterial toxin–antitoxin (TA) systems and allows cells to cope with stress. The ST23 GBS strains carrying this prophage were not pathogenic to tilapia, but the strains without the prophage or carrying the pophage that had gene mutation or deletion, especially the deletion of YafQ/DinJ structure, were highly pathogenic to tilapia. In conclusion, human ST23 GBS is highly pathogenic to fish, which may be related to the phage recombination.

Whole-Genome Sequence of Streptococcus agalactiae Strain S13, Isolated from a Fish Eye from a Nile Tilapia Farm in Southern Brazil

Streptococcus agalactiae is an important pathogen to world aquaculture due to its high mortality rates in fish farms and consequent economic losses. Our study presents the complete genome sequence of strain S13, isolated from a tilapia farm outbreak in southern Brazil.

Genomic comparison of virulent and non-virulent serotype V ST1 Streptococcus agalactiae in fish

Streptococcus agalactiae or Group B Streptococcus (GBS) is the major pathogen causing pneumonia and meningitis in human, mastitis in dairy cows, and streptococcal disease in tilapia. Previous studies have shown that fish GBS strains are correlated with human GBS strains in evolution and might have cross-host infection ability. Although the invasive disease caused by ST1 GBS in non-pregnant adults and cows is increasing worldwide, infection of fish by ST1 GBS has not been reported. The aim of this study was to determine whether ST1 GBS was virulent in fish and to investigate the genomic characteristics of ST1 GBS strains with different pathogenicity in tilapia. The human-derived serotype V ST1 GBS strains NNA048 and NNA038 were used to intraperitoneally challenge Nile tilapia (Oreochromis niloticus) with doses of 1.0×10⁹CFU/fish, 1.0×10⁷CFU/fish, and 1.0×10⁵CFU/fish, respectively. The cumulative mortality rates of NNA048 infection at three different doses were 100.00%, 83.33%, and 40.00%. In contrast, there were no any sick or dead fish in NNA038 infection group. Histopathological results indicated that challenge of tilapia with NNA048 caused different degree of degeneration and necrosis in brain, liver, spleen, head kidney, and gut, and a large number of blue-stained Streptococcus granules were observed in the tissues. In contrast, there were no any lesions in the tissues of tilapia that were challenged with NNA038. Genome comparison showed that the major genome differences between NNA048 and NNA038 were attributed to the different phage sequences, and there was a 49.8kb length, intact phage sequence encoding 68 proteins in NNA048 genome. SNV and Indels analysis between NNA038 and NNA048 genomes indicated that there were a total of 96 SNVs, 5 deletions and 1 insert. Taken together, serotype V ST1 GBS was comprised of virulent and nonvirulent strains to tilapia, and gene rearrangement might be the main reason of causing different levels of virulence between strains.

The immune response of the C-Jun in the black tiger shrimp (Penaeus monodon) after bacterial infection

The transcription factor C-Jun widely exists in vertebrates and invertebrates and plays an important role in various kinds of stimulus response. In this study, PmC-jun gene was first cloned from Penaeus monodon. The full-length cDNA of PmC-jun was 1857 bp in length and included an 879 bp open reading frame (ORF), which encoded 293 amino acids. qRT-PCR analysis results showed that PmC-jun mRNAs were ubiquitously expressed in all the examined tissues. The highest expression level was observed in gill, followed by hepatopancreas. The expression patterns of PmC-jun after Vibrio harveyi and Streptococcus agalactiae injections were studied by qRT-PCR experiment. PmC-jun increased obviously in the gill and hepatopancreas. The expression pattern of PmC-jun in the hepatopancreas was further studied using in situ hybridization (ISH) method. The mRNA expression level of PmC-jun significantly increased in the hepatopancreas after bacterial infection. The expression sites of PmC-jun were almost unchanged. PmC-jun played a regulatory role in pathogen invasion.