Invasive infection with Streptococcus iniae in Taiwan

Streptococcus iniae in aquaculture: a review of pathogenesis, virulence, and antibiotic resistance

One of the main challenges in aquaculture is pathogenic bacterial control. Streptococcus iniae stands out for its ability to cause high mortality rates in populations of commercially important fish populations and its recent recognition as an emerging zoonotic pathogen. The rise in identifying over 80 strains some displaying antibiotic resistance coupled with the emerging occurrence of infections in marine mammal species and wild fish underscores the urgent need of understanding pathogenesis, virulence and drug resistance mechanisms of this bacterium. This understanding is crucial to ensure effective control strategies. In this context, the present review conducts a bibliometric analysis to examine research trends related to S. iniae, extending into the mechanisms of infection, virulence, drug resistance and control strategies, whose relevance is highlighted on vaccines and probiotics to strengthen the host immune system. Despite the advances in this field, the need for developing more efficient identification methods is evident, since they constitute the basis for accurate diagnosis and treatment.

Bacterial and host factors involved in zoonotic Streptococcal meningitis

Zoonotic streptococci cause several invasive diseases with high mortality rates, especially meningitis. Numerous studies elucidated the meningitis pathogenesis of zoonotic streptococci, some specific to certain bacterial species. In contrast, others are shared among different bacterial species, involving colonization and invasion of mucosal barriers, survival in the bloodstream, breaching the blood-brain and/or blood-cerebrospinal fluid barrier to access the central nervous system, and triggering inflammation of the meninges. This review focuses on the recent advancements in comprehending the molecular and cellular events of five major zoonotic streptococci responsible for causing meningitis in humans or animals, including Streptococcus agalactiae, Streptococcus equi subspecies zooepidemicus, Streptococcus suis, Streptococcus dysgalactiae, and Streptococcus iniae. The underlying mechanism was summarized into four themes, including 1) bacterial survival in blood, 2) brain microvascular endothelial cell adhesion and invasion, 3) penetration of the blood-brain barrier, and 4) activation of the immune system and inflammatory reaction within the brain. This review may contribute to developing therapeutics to prevent or mitigate injury of streptococcal meningitis and improve risk stratification.

Comparative genomics analysis of Streptococcus iniae isolated from Trachinotus ovatus: novel insight into antimicrobial resistance and virulence differentiation

BACKGROUND

Streptococcus iniae is an important fish pathogen that cause significant economic losses to the global aquaculture industry every year. Although there have some reports on the genotype of S.iniae and its relationship with virulence, no genome-scale comparative analysis has been performed so far. In our previous work, we characterized 17 isolates of S.iniae from Trachinotus ovatus and divided them into two genotypes using RAPD and rep-PCR methods. Among them, BH15-2 was classified as designated genotype A (in RAPD) and genotype 1 (in rep-PCR), while BH16-24 was classified as genotype B and genotype 2. Herein, we compared the differences in growth, drug resistance, virulence, and genome between BH15-2 and BH16-24.

RESULTS

The results showed that the growth ability of BH16-24 was significantly faster than that of BH15-2 at the exponential stage. Antimicrobial tests revealed that BH15-2 was susceptible to most of the tested antibiotics except neomycin and gentamycin. In contrast, BH16-24 was resistant to 7 antibiotics including penicillin, sulfasomizole, compound sulfamethoxazole tablets, polymyxin B, spectinomycin, rifampin and ceftazidime. Intraperitoneal challenge of T.ovatus, showed that the LD50 value of BH15-2 was 4.0 × 102 CFU/g, while that of BH16-24 was 1.2 × 105 CFU/g. The genome of S.iniae BH15-2 was 2,175,659 bp with a GC content of 36.80%. Meanwhile, the genome of BH16-24 was 2,153,918 bp with a GC content of 36.83%. Comparative genome analysis indicated that compared with BH15-2, BH16-24 genome had a large-scale genomic inversion fragment, at the location from 502,513 bp to 1,788,813 bp, resulting in many of virulence and resistance genes differentially expression. In addition, there was a 46 kb length, intact phage sequence in BH15-2 genome, which was absent in BH16-24.

CONCLUSION

Comparative genomic studies of BH15-2 and BH16-24 showed that the main difference is a 1.28 Mbp inversion fragment. The inversion fragment may lead to abnormal expression of drug resistant and virulence genes, which is believed to be the main reason for the multiple resistance and weakened virulence of BH16-24. Our study revealed the potential mechanisms in underlying the differences of multidrug resistance and virulence among different genotypes of S.iniae.

Improving the diagnosis of Streptococcus iniae using a novel probe-based qPCR assay combined with an enrichment step

Streptococcus iniae is a bacterial pathogen that causes streptococcosis, leading to significant losses in fish aquaculture globally. This study reported a newly developed probe-based quantitative polymerase chain reaction (qPCR) method for the detection of S. iniae. The primers and probes were designed to target the lactate oxidase gene. The optimized method demonstrated a detection limit of 20 copies per reaction and was specific to S. iniae, as evidenced by no cross-reactivity when assayed against genetic materials extracted from 23 known aquatic animal pathogens, and fish samples infected with Streptococcus agalactiae or Streptococcus dysgalactiae. To validate the newly developed qPCR protocol with field samples, fish specimens were systematically investigated following the Food and Agriculture Organization of the United Nations & Network of Aquaculture Centres in Asia-Pacific three diagnostic levels approach, which integrated basic and advanced techniques for disease diagnosis, including observation of gross signs (level I), bacterial isolation (level II), qPCR and 16S rDNA sequencing (level III). The result showed that 7/7 affected farms (three Asian seabass farms and four tilapia farms) experiencing clinical signs of streptococcosis were diagnosed positive for S. iniae. qPCR assays using DNA extracted directly from fish tissue detected S. iniae in 11 out of 36 fish samples (30.6%), while 24 out of 36 samples (66.7%) tested positive after an enrichment step, including apparently healthy fish from affected farms. Bacterial isolation of S. iniae was only successful in a proportion of clinically diseased fish but not in healthy-looking fish from the same farm. Overall, the newly developed qPCR protocol combined with enrichment would be a useful tool for the diagnosis and surveillance of S. iniae infections in fish populations, thereby aiding in the disease control and prevention.

Phenotypic and Genotypic Characterization of Antimicrobial Resistance in Streptococci Isolated from Human and Animal Clinical Specimens

Recently, the phenomenon of infection of humans as hosts by animal pathogens has been increasing. Streptococcus is an example of a genus in which bacteria overcome the species barrier. Therefore, monitoring infections caused by new species of human pathogens is critical to their spread. Seventy-five isolates belonging to streptococcal species that have recently been reported as a cause of human infections with varying frequency, were tested. The aim of the study was to determine the drug resistance profiles of the tested strains, the occurrence of resistance genes and genes encoding the most important streptococcal virulence factors. All tested isolates retained sensitivity to β-lactam antibiotics. Resistance to tetracyclines occurred in 56% of the tested strains. We have detected the MLS_B type resistance (cross-resistance to macrolide, lincosamide, and streptogramin B) in 20% of the tested strains. 99% of the strains had tetracycline resistance genes. The erm class genes encoding MLS_B resistance were present in 47% of strains. Among the strains with MLS_B resistance, 92% had the streptokinase gene, 58% the streptolysin O gene and 33% the streptolysin S gene. The most extensive resistance concerned isolates that accumulated the most traits and genes, both resistance genes and virulence genes, increasing their pathogenic potential. Among the tested strains, the gene encoding streptokinase was the most common. The results of the prove that bacteria of the species S. uberis, S. dysgalactiae and S. gallolyticus are characterized by a high pathogenic potential and can pose a significant threat in case of infection of the human body.

Whole-Genome Sequence of Streptococcus iniae Strain AH1, Isolated from Hybrid Tilapia (Oreochromis niloticus × Oreochromis aureus)

Here, we describe the whole-genome sequence of Streptococcus iniae strain AH1, which was isolated from moribund farmed hybrid tilapia (Oreochromis niloticus × Oreochromis aureus) in Saudi Arabia. The genome is composed of a single linear chromosome of 2,068,661 bp, with a G+C content of 36.8%.

Mooseer (Allium hirtifolium) boosts growth, general health status, and resistance of rainbow trout (Oncorhynchus mykiss) against Streptococcus iniae infection

In large-scale aquaculture, the fast growth rate of fish is positively influenced by feed additives such as medicinal plants. This is however; infectious disease may reduce fish growth and cause devastating economic loss. The present study investigated in vitro antibacterial efficacy of Mooseer (Allium hirtifolium) extract against Streptococcus iniae and its in vivo effects on growth, biochemical parameters, innate immunity of rainbow trout (Oncorhynchus mykiss). Therefore, six experimental diets were designed to include different levels of Mooseer from zero (as control), 5, 10, 15, 20, and 25 g per kg diet respectively referred to as M1 to M5. Results from the antibacterial evaluation showed that Mooseer extract inhibits S. iniae growth with MIC and MBC values of 128 and 256 μg ml^-1. Appreciable results were obtained in the groups supplemented with Mooseer. Mooseer enhanced growth performance, and modulated serum biochemical and immunological parameters (total protein, albumin, triglyceride, glucose, cortisol, cholesterol, lysozyme, Ig, ACH50, ALP, and protease activity), and liver enzymes (ALT, AST and ALP). The greatest effects were found for higher doses of Mooseer supplementation (M4 and M5). Meanwhile, results from the survival rate of fish challenged with S. iniae showed higher survival in M2 and M4 treatments. The present findings suggest the beneficial use of Mooseer in rainbow trout diet, with 20 g kg^-1 inclusion as the recommended dose.

Pathogenicity and drug resistance of animal streptococci responsible for human infections

Bacteria of the genus Streptococcus, earlier considered typically animal, currently have also been causing infections in humans. It is necessary to make clinicians aware of the emergence of new species that may cause the development of human diseases. There is an increasing frequency of isolation of streptococci such as S. suis, S. dysgalactiae, S. iniae and S. equi from people. Isolation of Streptococcus bovis/Streptococcus equinus complex bacteria has also been reported. The streptococcal species described in this review are gaining new properties and virulence factors by which they can thrive in new environments. It shows the potential of these bacteria to changes in the genome and the settlement of new hosts. Information is presented on clinical cases that concern streptococcus species belonging to the groups Bovis, Pyogenic and Suis. We also present the antibiotic resistance profiles of these bacteria. The emerging resistance to β-lactams has been reported. In this review, the classification, clinical characteristics and antibiotic resistance of groups and species of streptococci considered as animal pathogens are summarized.

Phenotype and multi-omics comparison of Staphylococcus and Streptococcus uncovers pathogenic traits and predicts zoonotic potential

BACKGROUND

Staphylococcus and Streptococcus species can cause many different diseases, ranging from mild skin infections to life-threatening necrotizing fasciitis. Both genera consist of commensal species that colonize the skin and nose of humans and animals, and of which some can display a pathogenic phenotype.

RESULTS

We compared 235 Staphylococcus and 315 Streptococcus genomes based on their protein domain content. We show the relationships between protein persistence and essentiality by integrating essentiality predictions from two metabolic models and essentiality measurements from six large-scale transposon mutagenesis experiments. We identified clusters of strains within species based on proteins associated to similar biological processes. We built Random Forest classifiers that predicted the zoonotic potential. Furthermore, we identified shared attributes between of Staphylococcus aureus and Streptococcus pyogenes that allow them to cause necrotizing fasciitis.

CONCLUSIONS

Differences observed in clustering of strains based on functional groups of proteins correlate with phenotypes such as host tropism, capability to infect multiple hosts and drug resistance. Our method provides a solid basis towards large-scale prediction of phenotypes based on genomic information.

Development of a real-time PCR assay for detection and quantification of Streptococcus iniae using the lactate permease gene

The aim of this study is the development and evaluation of a rapid and accurate quantitative PCR (qPCR)-based protocol for detection of zoonotic pathogen Streptococcus iniae in bacterial cultures and tissues of diseased fish. For this purpose, the lactate permease-encoding (lldY) gene was selected as a target for the design of S. iniae-specific primers based on comparative genomic analysis using 45 sequences retrieved from NCBI genome database. Specificity and applicability of these primers were tested using 115 bacterial strains and fish tissues infected with S. iniae. Sensitivity, reproducibility and efficiency of qPCR assay were also determined. The developed qPCR assay showed 100% specificity with pure bacterial cultures or DNA extracted from S. iniae or tissues of fish infected with the bacterium. The method has high sensitivity with a detection limit of 1.12 × 10¹ amplicon copies per assay (equivalent to 2 × 10^-9  ng/µl) using bacterial DNA and of 1.44 × 10¹ gene copies in tissues of fish infected with S. iniae. In conclusion, this qPCR protocol provides an accurate and sensitive alternative for the identification of S. iniae and its detection on fish tissues that can be implemented as a routine tool in microbiological laboratories.

Streptococcus iniae associated mass marine fish kill off Western Australia

Streptococcus iniae causes high mortality in cultured and wild fish stocks globally. Since the first report in captive Amazon river dolphins Inia geoffrensis in 1976, it has emerged in finfish across all continents except Antarctica. In March 2016, an estimated 17000 fish were observed dead and dying along a remote 70 km stretch of the Kimberley coastline north of Broome, Western Australia. Affected species included finfish (lionfish Pterois volitans, angelfish Pomacanthus sp., stripey snapper Lutjanus carponotatus, sand bass Psammoperca waigiensis, yellowtail grunter Amniataba caudavittata, damselfish Pomacentridae sp.), flatback sea turtles Natator depressus, and olive (Aipysurus laevis) and black-ringed (Hydrelaps darwiniensis) sea snakes. Moribund fish collected during the event exhibited exophthalmia and abnormal behaviour, such as spiralling on the surface or within the water column. Subsequent histopathological examination of 2 fish species revealed bacterial septicaemia with chains of Gram-positive cocci seen in multiple organs and within brain tissue. S. iniae was isolated and identified by bacterial culture, species-specific PCR, Matrix-Assisted Laser Desorption Ionisation Time-Of-Flight (MALDI-TOF) and biochemical testing. This is the first report of S. iniae associated with a major multi-species wild marine fish kill in Australia. Extreme weather events in the region including a marked decrease in water temperatures, followed by an extended period of above-average coastal water temperatures, were implicated as stressors potentially contributing to this outbreak.

Multilocus sequence analysis of diverse Streptococcus iniae isolates indicates an underlying genetic basis for phenotypic heterogeneity

Streptococcus iniae is a Gram-positive, opportunistically zoonotic bacterium infective to a wide variety of farmed and wild fish species worldwide. Outbreaks in wild fish can have detrimental environmental and cultural impacts, and mortality events in aquaculture can result in significant economic losses. As an emerging or re-emerging pathogen of global significance, understanding the coalescing factors contributing to piscine streptococcosis is crucial for developing strategies to control infections. Intraspecific antigenic and genetic variability of S. iniae has made development of autogenous vaccines a challenge, particularly where the diversity of locally endemic S. iniae strains is unknown. This study genetically and phenotypically characterized 11 S. iniae isolates from diseased wild and farmed fish from North America, Central America, and the Caribbean. A multilocus sequence analysis (MLSA) scheme was developed to phylogenetically compare these isolates to 84 other strains of Streptococcus spp. relevant to aquaculture. MLSA generated phylogenies comparable to established genotyping methods, and isolates formed distinct clades related to phenotype and host species. The endothelial Oreochromis mossambicus bulbus arteriosus cell line and whole blood from rainbow trout Oncorhynchus mykiss, Nile tilapia Oreochromis niloticus, and white sturgeon Acipenser transmontanus were used to investigate the persistence and virulence of the 11 isolates using in vitro assays. In vivo challenges using an O. niloticus model were used to evaluate virulence by the intragastric route of infection. Isolates showed significant differences (p < 0.05) in virulence and persistence, with some correlation to genogroup, establishing a basis for further work uncovering genetic factors leading to increased pathogenicity.

Functional Analysis of Two Novel Streptococcus iniae Virulence Factors Using a Zebrafish Infection Model

Streptococcus iniae is a major fish pathogen that contributes to large annual losses in the aquaculture industry, exceeding US$100 million. It is also reported to cause opportunistic infections in humans. We have recently identified two novel S. iniae virulence factors, an extracellular nuclease (SpnAi) and a secreted nucleotidase (S5nAi), and verified their predicted enzymatic activities using recombinant proteins. Here, we report the generation of green fluorescent S. iniae spnAi and s5nAi deletion mutants and their evaluation in a transgenic zebrafish infection model. Our results show nuclease and nucleotidase activities in S. iniae could be attributed to SpnAi and S5nAi, respectively. Consistent with this, larvae infected with the deletion mutants demonstrated enhanced survival and bacterial clearance, compared to those infected with wild-type (WT) S. iniae. Deletion of spnAi and s5nAi resulted in sustained recruitment of neutrophils and macrophages, respectively, to the site of infection. We also show that recombinant SpnAi is able to degrade neutrophil extracellular traps (NETs) isolated from zebrafish kidney tissue. Our results suggest that both enzymes play an important role in S. iniae immune evasion and might present potential targets for the development of therapeutic agents or vaccines.

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.

Nile tilapia fry fed on antimicrobial peptide Epinecidin-1-expressing Artemia cyst exhibit enhanced immunity against acute bacterial infection

Artemia are often used as a live feed for fry in aquaculture. We have previously demonstrated that supplementing adult zebrafish feed with Artemia, which express an Epinephelus coioides-derived antimicrobial peptide, Epinecidin-1 (Epi-1), protects against bacterial infection. Thus, Artemia may serve as a bioreactor for producing biofunctional molecules. However, the application of Epi-1 transgenic Artemia in larval aquaculture of commercial fish species has not been investigated. Here we used a Tol2-transposon system to generate stable Epi-1 expressing Artemia. Nile tilapia (Oreochromis niloticus) fry were then fed with decapsulated transgenic cysts and acutely challenged with Gram-positive Streptococcus iniae or Gram-negative Vibrio vulnificus (204). Survival analysis revealed that tilapia fry fed with Epi-1 transgenic cysts were resistant to acute bacterial infection. Immune-related gene expression profiling showed that S. iniae and V. vulnificus inoculations produced distinct immunomodulatory effects in the tilapia fry. Upon S. iniae infection, tilapia fry fed on control diet exhibited an immune response dominated by Tlr-7/MyD88, wherein Tnf-α, Il-8 and Cxcl-10 expression were all induced; conversely, the tilapia fry fed with Epi-1 transgenic cysts showed a Tlr-2/Tlr-5-dominant immune response, marked by the induction of Il-1β, Il-8 and Il-12 expression. However, after V. vulnificus (204) infection control fry exhibited a Tlr-2/MyD88/Traf-6-dominant response with activation of Tnf-α and Il-8 expression; meanwhile tilapia fry fed on Epi-1 transgenic cyst showed a dominant Tlr-2/Tlr-5-mediated immune response, including induction of Il-1β, Il-8, Il-12, and Cxcl-10 expression. These findings suggest that feeding larval fish fry with Epi-1 transgenic Artemia cysts confers enhanced immunity toward bacterial challenge. Epi-1 transgenic cysts should therefore be considered as a potential functional feed for larval aquaculture.

Complete Genome Sequence of Streptococcus iniae 89353, a Virulent Strain Isolated from Diseased Tilapia in Taiwan

Streptococcus iniae 89353 is a virulent strain isolated from diseased tilapia in Taiwan. The full-genome sequence of S. iniae 89353 is 2,098,647 bp. The revealed genome information will be beneficial for identification and understanding of potential virulence genes of Streptococcus iniae and possible immunogens for vaccine development against streptococcosis.

Fatal bacterial septicemia in a bottlenose dolphin Tursiops truncatus caused by Streptococcus iniae

A captive 8 yr old male bottlenose dolphin Tursiops truncatus succumbed to septicemia with multisystemic inflammation including suppurative enteritis, encephalitis, and pneumonia with chronic pancreatitis. A pure culture of beta-hemolytic, catalase- and oxidase-negative, Gram-positive cocci was isolated from the hilar lymph nodes and pancreas. The isolate was identified by 16S rDNA sequencing as Streptococcus iniae. Histological examination of the digestive system revealed a mixed infection of both bacteria and fungus. Recognized as a pathogen in fish, dolphins, and humans, this is the first report of S. iniae in a dolphin in mainland China. As the number of managed animals in oceanariums is increasing, so is the frequency of contact with fish used as food for marine mammals and humans, highlighting the importance of education and appropriate personal protective protocols to minimize the risk of transmission. An understanding of marine mammal infectious disease organisms is essential to ensuring the health of marine mammals and humans coming into contact with such animals and their food. This study illustrates a systematic clinical, microbiological, and pathological investigation into a septicemic bottlenose dolphin infected with S. iniae. Our findings provide useful information for those involved in the diagnosis and control of infectious diseases in marine mammals and offer insight into an important zoonotic pathogen.

Characterization and identification of streptococci from golden pompano in China

Streptococcal infections cause significant mortality and high economic losses in the fish farm industry worldwide, including in the culture of golden pompano Trachinotus ovatus L., a species gaining popularity in China. A total of 9 streptococcal strains were isolated from cage-cultured diseased golden pompano in Beihai, Zhanjing, and Shenzhen, China, between 2012 and 2014. Conventional and rapid identification systems were used to determine that the isolates were Streptococcus agalactiae, S. iniae, and S. dysgalactiae subsp. dysgalactiae. All isolates were gram-positive cocci cells in pairs or short-chain, non-motile, catalase negative, α or β hemolytic cocci. The results of multiplex PCR assays and 16S rRNA BLAST analysis also showed that the β hemolytic strains were S. agalactiae and S. iniae and the α hemolytic strain was S. dysgalactiae subsp. dysgalactiae, respectively. Pathogenicity assays revealed that S. agalactiae (lethal dose [LD50]: 6.38 × 10(4) CFU ml(-1)) was more virulent for golden pompano than S. iniae (LD50: 1.47 × 10(7) CFU ml(-1)) and S. dysgalactiae subsp. dysgalactiae (LD50: 2.57 × 10(6) CFU ml(-1)) when they were challenged by intraperiotoneal (i.p.) injection. The results of antibiotic susceptibility showed that all strains were extremely susceptible to cefradine, erythromycin, and cefotaxime but resistant to gentamicin, penicillin G, novobiocin, neomycin, ciprofloxacin, roxithromycin, furazolidone, enrofloxacin, norfloxacin, kanamycin, ampicillin, tetracycline, and vancomycin This is the first report of a phenomenon of golden pompano coinfection with S. agalactiae and S. iniae, which will contribute to the diagnosis and prevention of streptococcicosis.

Cloning and Characterization of Surface-Localized α-Enolase of Streptococcus iniae, an Effective Protective Antigen in Mice

Streptococcus iniae is a major fish pathogen that can also cause human bacteremia, cellulitis and meningitis. Screening for and identification of protective antigens plays an important role in developing therapies against S. iniae infections. In this study, we indicated that the α-enolase of S. iniae was not only distributed in the cytoplasm and associated to cell walls, but was also secreted to the bacterial cell surface. The functional identity of the purified recombinant α-enolase protein was verified by its ability to catalyze the conversion of 2-phosphoglycerate (2-PGE) to phosphoenolpyruvate (PEP), and both the recombinant and native proteins interacted with human plasminogen. The rabbit anti-rENO serum blockade assay shows that α-enolase participates in S. iniae adhesion to and invasion of BHK-21 cells. In addition, the recombinant α-enolase can confer effective protection against S. iniae infection in mice, which suggests that α-enolase has potential as a vaccine candidate in mammals. We conclude that S. iniae α-enolase is a moonlighting protein that also associates with the bacterial outer surface and functions as a protective antigen in mice.

Zebrafish as a model for zoonotic aquatic pathogens

Aquatic habitats harbor a multitude of bacterial species. Many of these bacteria can act as pathogens to aquatic species and/or non-aquatic organisms, including humans, that come into contact with contaminated water sources or colonized aquatic organisms. In many instances, the bacteria are not pathogenic to the aquatic species they colonize and are only considered pathogens when they come into contact with humans. There is a general lack of knowledge about how the environmental lifestyle of these pathogens allows them to persist, replicate and produce the necessary pathogenic mechanisms to successfully transmit to the human host and cause disease. Recently, the zebrafish infectious disease model has emerged as an ideal system for examining aquatic pathogens, both in the aquatic environment and during infection of the human host. This review will focus on how the zebrafish has been used successfully to analyze the pathogenesis of aquatic bacterial pathogens.

Complete Genome Sequence of a Virulent Strain, Streptococcus iniae ISET0901, Isolated from Diseased Tilapia

Streptococcus iniae ISET0901 is a virulent strain isolated in 2007 from diseased tilapia. Its full genome is 2,070,856 bp. The availability of this genome will allow comparative genomics to identify virulence genes important for the pathogenesis of streptococcosis caused by S. iniae, as well as possible immunogens for vaccine development.

Complete Genome Sequence of the Attenuated Novobiocin-Resistant Streptococcus iniae Vaccine Strain ISNO

Streptococcus iniae ISNO is an attenuated novobiocin-resistant vaccine strain. Its full genome is 2,070,182 bp in length. The availability of this genome will allow comparative genomics to identify potential virulence genes important for pathogenesis of S. iniae and potential mechanisms associated with novobiocin resistance in this strain.

Fatal septicemia caused by the zoonotic bacterium Streptococcus iniae during an outbreak in Caribbean reef fish

An outbreak of Streptococcus iniae occurred in the early months of 2008 among wild reef fish in the waters of the Federation of St Kitts and Nevis, lasting almost 2 months. Moribund and dead fish were collected for gross, histological, bacteriological, and molecular analysis. Necropsy findings included diffuse fibrinous pericarditis, pale friable livers, and serosal petechiation. Cytological and histological analysis revealed granulocytic and granulomatous inflammation with abundant coccoid bacterial organisms forming long chains. Necrosis, inflammation, and vasculitis were most severe in the pericardium, meninges, liver, kidneys, and gills. Bacterial isolates revealed β-hemolytic, Gram-positive coccoid bacteria identified as S. iniae by amplification and 16S ribosomal RNA gene sequencing. Results from biochemical and antimicrobial susceptibility analysis, together with repetitive element palindromic polymerase chain reaction fingerprinting, suggest that a single strain was responsible for the outbreak. The inciting cause for this S. iniae-associated cluster of mortalities is unknown.

Fitness cost, gyrB mutation, and absence of phosphotransferase system fructose specific IIABC component in novobiocin-resistant Streptococcus iniae vaccine strain ISNO

To understand the fitness cost of novobiocin-resistance in an attenuated Streptococcus iniae vaccine strain ISNO compared to its virulent parent strain ISET0901, cell proliferation rate of the two strains were compared to each other. Our results revealed that the cell proliferation rates of ISNO were significantly (P<0.05) smaller than that of ISET0901. To understand whether there was any mutation at the target site of novobiocin, DNA gyrase subunit B (gyrB) was sequenced from both strains. Sequencing results revealed a point mutation of AGA to AGC, resulting in a deduced amino acid substitution of R635S. To determine whether any unique DNA sequence was present in ISET0901 but absent in ISNO, PCR-select bacterial genome subtractive hybridization was performed. A phosphotransferase system fructose specific IIABC component sequence was confirmed to be present in ISET0901 but absent in ISNO. Using genomic DNAs from ten field-strains of S. iniae as templates, the phosphotransferase system fructose specific IIABC component sequence was found to be present in five highly virulent strains, but absent in five avirulent strains. Taken together, our results suggest that: (1) As fitness cost of novobicin resistance, ISNO had significantly smaller cell proliferation rate; (2) point mutation at target site gyrB resulting in R635S substitution was associated with novobiocin resistance in ISNO; and (3) phosphotransferase system fructose specific IIABC component was associated with virulence of S. iniae.

Induction and characterization of lysogenic bacteriophages from Streptococcus iniae

AIMS

To investigate the presence of prophage in Streptococcus iniae, a highly problematic fish pathogen.

METHODS AND RESULTS

Cross-spotting assays and mitomycin C inductions were conducted to screen for prophage in 48 Strep. iniae isolates. Bacteriophages were characterized by plaque assays, transmission electron microscopy and DNA restriction enzyme digestion. Plaque assays confirmed prophages in 14·6% of isolates. Phages vB_SinS-44, vB_SinS-45, vB_SinS-46 and vB_SinS-48 lysed 78·5% of Strep. iniae isolates and displayed distinctive host ranges. Microscopy revealed virions exhibiting long, non-contractile tails and isometric heads consistent with phages from the family Siphoviridae. Restriction digests revealed genome sizes ranging from 27·5 to 66·3 kbp, with distinct cutting patterns that indicate the presence of related prophages in bacteria isolated from different geographic regions.

CONCLUSIONS

The rate of prophage carriage found is comparably low and induction rates varied between phages. The four characterized Siphoviridae phages have broad host ranges within the Strep. iniae isolates.

SIGNIFICANCE AND IMPACT OF THE STUDY

This is the first description and characterization of lysogenic phages from Strep. iniae. These phages are candidates for research and diagnosis of the bacterium and their identification should accelerate the discovery of lytic phages to be trialled against Strep. iniae infections in fish.

Genome characterization and population genetic structure of the zoonotic pathogen, Streptococcus canis

Background

Streptococcus canis is an important opportunistic pathogen of dogs and cats that can also infect a wide range of additional mammals including cows where it can cause mastitis. It is also an emerging human pathogen.

Results

Here we provide characterization of the first genome sequence for this species, strain FSL S3-227 (milk isolate from a cow with an intra-mammary infection). A diverse array of putative virulence factors was encoded by the S. canis FSL S3-227 genome. Approximately 75% of these gene sequences were homologous to known Streptococcal virulence factors involved in invasion, evasion, and colonization. Present in the genome are multiple potentially mobile genetic elements (MGEs) [plasmid, phage, integrative conjugative element (ICE)] and comparison to other species provided convincing evidence for lateral gene transfer (LGT) between S. canis and two additional bovine mastitis causing pathogens (Streptococcus agalactiae, and Streptococcus dysgalactiae subsp. dysgalactiae), with this transfer possibly contributing to host adaptation. Population structure among isolates obtained from Europe and USA [bovine = 56, canine = 26, and feline = 1] was explored. Ribotyping of all isolates and multi locus sequence typing (MLST) of a subset of the isolates (n = 45) detected significant differentiation between bovine and canine isolates (Fisher exact test: P = 0.0000 [ribotypes], P = 0.0030 [sequence types]), suggesting possible host adaptation of some genotypes. Concurrently, the ancestral clonal complex (54% of isolates) occurred in many tissue types, all hosts, and all geographic locations suggesting the possibility of a wide and diverse niche.

Conclusion

This study provides evidence highlighting the importance of LGT in the evolution of the bacteria S. canis, specifically, its possible role in host adaptation and acquisition of virulence factors. Furthermore, recent LGT detected between S. canis and human bacteria (Streptococcus urinalis) is cause for concern, as it highlights the possibility for continued acquisition of human virulence factors for this emerging zoonotic pathogen.

Establishment of a model of Streptococcus iniae meningoencephalitis in Nile tilapia (Oreochromis niloticus)

Streptococcus iniae is an invasive pathogen causing meningitis and other lesions in various fish species. Furthermore, S. iniae is an emerging zoonotic agent that causes cellulitis in man. The aims of this study were to establish an intraperitoneal infection model for S. iniae in Nile tilapia (Oreochromis niloticus) and to develop a new histopathological scoring system to reflect the degree and extent of inflammation as well as the presence of necrosis in the brain and eye. Intraperitoneal administration of 10(6) colony-forming units (CFU) led to 80% mortality and numerous fish developing clinical signs of central nervous system dysfunction. Microscopical examination of four regions of the brain (olfactory bulb, cerebellum, cerebrum and optical lobe) and the eye revealed the presence of lymphohistiocytic leptomeningitis, meningoencephalitis and endophthalmitis. Lesions were dominated by macrophages that often contained intracellular bacteria. Necrosis was recorded in some cases. Bacteriological screening revealed that multiple organs, including brain and eye, were infected with S. iniae and S. iniae colonized the scales and gills in high number. S. iniae was detected in tank water during the first week post infection, suggesting that infected tilapia might shed up to 3 × 10(7) CFU of S. iniae within 24 h. A multiplex polymerase chain reaction allowed confirmation of the challenge strain by detection of the virulence factors simA, scpI, cpsD, pgi, pgm and sagA.

Epidemiology and pathogenicity of zoonotic streptococci

Zoonotic infections caused by Streptococcus spp. have been neglected in spite of the fact that frequency and severity of outbreaks increased dramatically in recent years. This may be due to non-identification since respective species are often not considered in human medical diagnostic procedures. On the other hand, an expanding human population concomitant with an increasing demand for food and the increased number of companion animals favour conditions for host species adaptation of animal streptococci. This review aims to give an overview on streptococcal zoonoses with focus on epidemiology and pathogenicity of four major zoonotic species, Streptococcus canis, Streptococcus equi sub. zooepidemicus, Streptococcus iniae and Streptococcus suis.

Efficacy of QCDCR formulated CpG ODN 2007 in Nile tilapia against Streptococcus iniae and identification of upregulated genes

The potential of using a QCDCR (quilA:cholesterol:dimethyl dioctadecyl ammonium bromide:carbopol:R1005 glycolipid) formulated CpG oligodeoxynucleotide (ODN), ODN 2007, to confer protection in Nile tilapia against Streptococcus iniae infection was evaluated in this study. At two days post treatment, QCDCR formulated ODN 2007 elicited significant (P<0.05) protection to Nile tilapia, with relative percent survival of 63% compared to fish treated by QCDCR alone. To understand the molecular mechanisms involved in the protective immunity elicited by ODN 2007, suppression subtractive cDNA hybridization technique was used to identify upregulated genes induced by ODN 2007. A total of 69 expressed sequence tags (ESTs) were identified from the subtractive cDNA library. Quantitative PCR revealed that 44 ESTs were significantly (P<0.05) upregulated by ODN 2007, including 29 highly (>10-fold) and 15 moderately (<10-fold) upregulated ESTs. Of all ESTs, putative peroxisomal sarcosine oxidase was upregulated the highest. The 69 ESTs only included six genes that had putative functions related to immunity, of which only two (putative glutaredoxin-1 and carboxypeptidase N catalytic chain) were confirmed to be significantly upregulated. Our results suggest that the protection elicited by ODN 2007 is mainly through innate immune responses directly or indirectly related to immunity.

Soft tissue infections caused by marine bacterial pathogens: epidemiology, diagnosis, and management

Skin and soft tissue infections (SSTIs) are one of the most common infection syndromes and may be caused by a large number of microorganisms. Some principles of aquatic injuries are different than those of land-based trauma. Wounds sustained in marine environment are exposed to a milieu of bacteria rarely encountered in different settings. These include Vibrio spp., Aeromonas spp., Shewanella spp., Erysipelothrix rhusiopathiae, Mycobacterium marinum, Streptococcus iniae, and other microbes. Failure to recognize and treat these uncommon pathogens in a timely manner may result in significant morbidity or death. These infections are frequently contracted as a result of recreational swimming, fishing injuries, or seafood handling. The spectrum of manifestations is wide, varying from cases of mild cellulitis, to severe life-threatening necrotizing fasciitis requiring radical surgery, to sepsis and death. This review will focus on the epidemiology, clinical manifestations, and treatment of SSTIs caused by the most important marine pathogens.

Towards control of Streptococcus iniae

Streptococcus iniae is an emerging zoonotic pathogen; such infections generally occur through injuries associated with preparing whole fresh fish for cooking. Those infected to date have been of Asian descent, are usually elderly (average age 68 years), and have had >/=1 underlying conditions that may predispose them to infection. Studies of the foundations of growth characteristics of S. iniae and its interactions with piscine host cells have recently been complemented by molecular studies. Advances in molecular biology have allowed research groups to identify numerous virulence factors and to explore their roles in the progression of S. iniae infection. Many of these virulence factors are homologous to those found in the major human pathogen S. pyogenes. An increased understanding of the properties of these factors and their effect on the success of infection is leading to novel approaches to control S. iniae infection; in particular, vaccination programs at fish farms have reduced the reservoir of infection for additional clinical cases.

The novel polysaccharide deacetylase homologue Pdi contributes to virulence of the aquatic pathogen Streptococcus iniae

The aquatic zoonotic pathogen Streptococcus iniae represents a threat to the worldwide aquaculture industry and poses a risk to humans who handle raw fish. Because little is known about the mechanisms of S. iniae pathogenesis or virulence factors, we established a high-throughput system combining whole-genome pyrosequencing and transposon mutagenesis that allowed us to identify virulence proteins, including Pdi, the polysaccharide deacetylase of S. iniae, that we describe here. Using bioinformatics tools, we identified a highly conserved signature motif in Pdi that is also conserved in the peptidoglycan deacetylase PgdA protein family. A Deltapdi mutant was attenuated for virulence in the hybrid striped bass model and for survival in whole fish blood. Moreover, Pdi was found to promote bacterial resistance to lysozyme killing and the ability to adhere to and invade epithelial cells. On the other hand, there was no difference in the autolytic potential, resistance to oxidative killing or resistance to cationic antimicrobial peptides between S. iniae wild-type and Deltapdi. In conclusion, we have demonstrated that pdi is involved in S. iniae adherence and invasion, lysozyme resistance and survival in fish blood, and have shown that pdi plays a role in the pathogenesis of S. iniae. Identification of Pdi and other S. iniae virulence proteins is a necessary initial step towards the development of appropriate preventive and therapeutic measures against diseases and economic losses caused by this pathogen.