Isolation and molecular characterization of streptococcal species recovered from clinical infections in farmed Nile tilapia (Oreochromis niloticus) in the Philippines.

Streptococcosis cause severe losses for global tilapia farming, especially in developing countries. The aim of this study was to identify and characterize streptococci recovered from Nile tilapia farmed in the Philippines. Moribund and apparently healthy fish were sampled from grow-out cages, ponds and hatcheries. Clinical signs observed included exophthalmia, eye opacity, ascites, lethargy, erratic swimming and haemorrhages. Results showed that both Streptococcus iniae and Streptococcus agalactiae were associated with disease in these sites. Consistent with global reports, including those from South-East Asia, S. agalactiae was more widespread than S. iniae. Molecular serotyping of the S. agalactiae isolates identified the serotype Ia and serotype Ib. Histopathological findings were meningitis, meningoencephalitis and septicaemia. Identical virulence profiles were found for all strains of S. iniae, while S. agalactiae strains were separated into virulence profile I and profile II. All strains were susceptible to the tested antibiotics and resistant to oxolinic acid. Only S. agalactiae serotype Ib showed resistance to sulphamethoxazole-trimethoprim. This is the first study from the Philippines to characterize the streptococci involved in disease outbreaks in tilapia aquaculture. Outputs from this study will promote the development of efficacious disease control strategies in tilapia farming for the Philippines and South-East Asia.

Therapeutic and Histopathological Effect of Aloe vera and Salvia officinalis Hydroethanolic Extracts against Streptococcus iniae in Rainbow Trout.

Some of the medicinal plants have antibacterial contents and appear to be proper alternatives for antibiotics in the treatment of streptococcal disease, which causes plenty of mortalities in fish farms annually. Therefore, this study investigated the therapeutic effect of Aloe vera and Salvia officinalis hydroethanolic extracts against Streptococcus iniae in rainbow trout. Plant extracts components were analyzed by Gas chromatography-mass spectrometry method and tested in vitro against S. iniae by disk diffusion assay. In in vivo, 480 rainbow trout (10±0.1 g) were distributed in 9 groups (with 3 replication), and all groups (except for the first group as the negative control that was injected with 100 µl of physiologic serum) were injected by 100 µl of LD50 (3.66×108.5CFU/ml) of S. iniae suspension, intraperitoneally. The fish of groups were treated by A. vera and S. officinalis extracts in doses 0 (positive control group was fed by commercial diet without plant extract), 0.5, 1, and 1.5% (supplemented diet) and 80 mg/kg body weight erythromycin for the next 10 days. At the end of the study period, tissue samples of the gills and livers of all groups were taken for the histopathological lesion assay. The results showed that A. vera and S. officinalis had antibacterial components as Cineol, and S. iniae was sensitive to both A. vera (MBC=4.067 mg/ml) and S. officinalis (MBC=5.185 mg/ml) extracts. At the end of the treatment period, there were no significant differences among erythromycin, A. vera (1.5%), and A. vera (1%) in terms of the mortality of the infected fish (P˂0.05). Moreover, A. vera (1.5%) showed a significantly lower mortality rate, compared to the positive control (P˂0.05). A. vera (1.5%) was the best group to moderate all histopathological lesions, compared to other groups. Accordingly, A. vera (1.5 %) is useful to treat streptococcosis (caused by S. iniae) and alter gill and liver histopathological lesions in rainbow trout.

Significance of Glutamate Racemase for the Viability and Cell Wall Integrity of Streptococcus iniae.

Streptococcus iniae is a pathogenic and zoonotic bacterium responsible for human diseases and mortality of many fish species. Recently, this bacterium has demonstrated an increasing trend for antibiotics resistance, which has warranted a search for new approaches to tackle its infection. Glutamate racemase (MurI) is a ubiquitous enzyme of the peptidoglycan synthesis pathway that plays an important role in the cell wall integrity maintenance; however, the significance of this enzyme differs in different species. In this study, we knocked out the MurI gene in S. iniae in order to elucidate the role of glutamate racemase in maintaining cell wall integrity in this bacterial species. We also cloned, expressed, and purified MurI and determined its biochemical characteristics. Biochemical analysis revealed that the MurI gene in S. iniae encodes a functional enzyme with a molecular weight of 30 kDa, temperature optimum at 35°C, and pH optimum at 8.5. Metal ions, such as Cu2+, Mn2+, Co2+ and Zn2+, inhibited the enzyme activity. MurI was found to be essential for the viability and cell wall integrity of S. iniae. The optimal growth of the MurI-deficient S. iniae mutant can be achieved only by adding a high concentration of D-glutamate to the medium. Membrane permeability assay of the mutant showed an increasing extent of the cell wall damage with time upon D-glutamate starvation. Moreover, the mutant lost its virulence when incubated in fish blood. Our results demonstrated that the MurI knockout leads to the generation of S. iniae auxotroph with damaged cell walls.

Antibacterial activity of Oliveria decumbens against Streptococcus iniae in Nile tilapia (Oreochromis niloticus) and its effects on serum and mucosal immunity and antioxidant status.

The aims of this study were to investigate the antibacterial, immunostimulatory and antioxidant properties of different derivatives of Oliveria decumbens, in vitro and in vivo. The GC-MS spectrometry analysis showed γ-terpinene as the most frequent compound in essential oil, whereas carvacrol and thymol were the most common ones in aromatic water. Plant essential oil and hydroethanolic extract showed a positive in vitro bactericidal activity against Streptococcus iniae as evaluated by disc diffusion, minimum inhibitory concentration and minimum bactericidal concentration methods. Also, in vivo resistance against S. iniae and immune and antioxidant responses of Nile tilapia (Oreochromis niloticus) were assayed after 60 days treatment with O. decumbens derivatives. Plant hydroethanolic extract and essential oil and their 1:1 combination were added to diet at 0 (negative control), 0.01, 0.1 and 1% (w:w). The plant aromatic water at doses of 0.0312, 0.0625 and 0.1250% were also used as bath treatment. The results showed that aromatic water at lowest dose was more effective than other treatments in increment of fish resistance against S. iniae (7.14% mortality in comparison with 50% mortalities in control fish) and modulation of post-challenge respiratory burst activity. The bactericidal activity and biochemical contents of skin mucus did not change significantly among treatments. The levels of superoxide dismutase and catalase antioxidant enzymes activities in spleen tissue were significantly higher in treatments received extract, essential oils and their combination in comparison to other groups, while treatments did not affect peroxidase level. In conclusion, administration of different derivatives of Oliveria decumbens showed remarkable antibacterial activity against streptococcosis and enhanced antioxidant status and post-challenge immunity in Nile tilapia.

Antimicrobial activity of the biopolymer chitosan against Streptococcus iniae.

The antimicrobial activity and mode of action of chitosan were evaluated against Streptococcus iniae, a pathogenic Gram-positive bacterium of fish worldwide. Cell proliferation kinetics were examined following exposure to varying concentrations of chitosan. The action of chitosan on S. iniae was also investigated by measuring agglutination activity, conductivity, and extracellular and intracellular bacterial adenosine triphosphate (ATP) levels. Chitosan exhibited antibacterial activity against S. iniae at concentrations of 0.1% and above and was lethal at a concentration of 0.4% and higher. The mechanism of antibacterial activity of chitosan at the inhibitory level of bacterial growth appears to hinge upon the interaction between chitosan and the oppositely charged bacterial surface. This interplay causes agglutination, which was readily observed grossly and microscopically. After interacting with the cell surface via adsorption, an efflux of intracellular ATP was documented, which suggests that chitosan disrupts the bacterial cell causing leakage of cytosolic contents and ultimately cell death. Results suggest chitosan may be worth evaluating as a natural alternative to antibiotic against S. iniae infection of fish.

Comparative single-dose pharmacokinetics of orally administered florfenicol in rainbow trout (Oncorhynchus mykiss, Walbaum, 1792) at health and experimental infection with Streptococcus iniae or Lactococcus garvieae.

This study evaluates changes in the pharmacokinetic behavior of a single oral dose of florfenicol in rainbow trouts experimentally infected with Lactococcus garvieae or Streptococcus iniae. One hundred and fifty fish were randomly divided into three equal groups: 1-healthy fish, 2-fish inoculated with S. iniae (2.87 × 107 CFU/ml, i.p.), and 3-fish inoculated with L. garvieae (6.8 × 105 CFU/ml, i.p.). Florfenicol was administered to all groups at 15 mg/kg by oral gavage. Blood sampling was performed at 0, 2, 3, 6, 8, 12, 24, 48, 72, and 120 hr after drug administration to each group, and plasma concentration of florfenicol was assayed by HPLC method. The MICs of florfenicol were 1.2 µg/ml and 5 µg/ml against L. garviae and S. iniae, respectively. Healthy fish showed higher values for most of the PK/PD parameters as compared to fish infected with L. garvieae which was reversed in fish infected with S. iniae. Fish infected with L. garvieae showed decreased relative bioavailability accompanied by increased volume of distribution at steady-state (Vdss ) and total body clearance (ClB ). Infection with S. iniae increased the peak concentration of drug after administration (Cmax) and decreased elimination half-life (T1/2 ß ), central compartment volume (Vc ), and Vdss . In conclusion, infection with these bacteria can affect the pharmacokinetic behavior of florfenicol in rainbow trouts as shown by decreased bioavailability and increased total body clearance and volume of distribution in L. garvieae infection and decreased volume of distribution accompanied by increased Cmax in S. iniae-infected fish.

Antibacterial Activities of Metabolites from Vitis rotundifolia (Muscadine) Roots against Fish Pathogenic Bacteria.

Enteric septicemia of catfish, columnaris disease and streptococcosis, caused by Edwardsiella ictaluri, Flavobacterium columnare and Streptococcus iniae, respectively, are the most common bacterial diseases of economic significance to the pond-raised channel catfish Ictalurus punctatus industry. Certain management practices are used by catfish farmers to prevent large financial losses from these diseases such as the use of commercial antibiotics. In order to discover environmentally benign alternatives, using a rapid bioassay, we evaluated a crude extract from the roots of muscadine Vitis rotundifolia against these fish pathogenic bacteria and determined that the extract was most active against F. columnare. Subsequently, several isolated compounds from the root extract were isolated. Among these isolated compounds, (+)-hopeaphenol (2) and (+)-vitisin A (3) were found to be the most active (bacteriostatic activity only) against F. columnare, with 24-h 50% inhibition concentrations of 4.0 ± 0.7 and 7.7 ± 0.6 mg/L, respectively, and minimum inhibitory concentrations of 9.1 ± 0 mg/L for each compound which were approximately 25X less active than the drug control florfenicol. Efficacy testing of 2 and 3 is necessary to further evaluate the potential for these compounds to be used as antibacterial agents for managing columnaris disease.

The effect of ß-1,3-glucan derived from Euglena gracilis (Algamune™ ) on the innate immunological responses of Nile tilapia (Oreochromis niloticus L.).

Algamune™ is a commercial additive produced from Euglena gracilis, providing a rich source of the ß-1,3-glucan paramylon. Isolated kidney phagocytes of Nile tilapia were incubated with graded doses (0, 8, 16, 32, 64 and 128 µg/ml) of Algamune™ and purified paramylon to gauge their ability to elicit the production of reactive oxygen species. A linear response was observed for extracellular superoxide anion for both sources but only Algamune™ for intracellular superoxide anion. After corroborating the immunostimulant properties ex vivo, a feeding trial was conducted to evaluate the dietary supplementation of Algamune™ (0, 100, 200, 400 and 800 mg/kg of diet) for Nile tilapia. Fish were fed for 3 weeks, after which, fish were sampled for blood and head kidney phagocytes. The remaining fish were challenged with Streptococcus iniae. Macrophage extracellular superoxide anion production was significantly elevated in fish fed diets with 200 mg of Algamune™ kg-1 when compared to fish fed the basal diet. Even though the disease challenge did not show statistical differences, it is worth mentioning that fish fed intermediate doses of Algamune™ had lowest numerical mortality values. Therefore, Algamune™ was demonstrated to enhance some immunological responses of tilapia both in ex vivo and in vivo.

Antibacterial Activity of Constituents from Mangosteen Garcinia mangostana Fruit Pericarp against Several Channel Catfish Pathogens.

Bacterial diseases cause major financial damage to the producers of Channel Catfish Ictalurus punctatus in the southeastern USA. The two most common bacterial diseases among pond-raised Channel Catfish are enteric septicemia of catfish, caused by the gram-negative bacterium Edwardsiella ictaluri, and columnaris disease, caused by the rod-shaped, gram-negative bacterium Flavobacterium columnare. Streptococcosis is another, less-common bacterial disease in catfish and is caused by the gram-positive coccus Streptococcus iniae. Catfish farmers typically rely on commercial antibiotics and other chemicals to prevent the economic damage from these diseases. Environmentally benign and efficacious alternatives to the currently used antibiotics and chemicals will tremendously help the catfish aquaculture industry. As part of our ongoing efforts in the search for such novel compounds, we investigated ethyl acetate and methanol extracts of mangosteen Garcinia mangostana fruit pericarp via bioassay-guided fractionation. Gamma-mangostin (γ-mangostin) was isolated and identified as the most promising active metabolite against F. columnare. One of the constituents in the mangosteen fruit pericarp, alpha-mangostin (α-mangostin), is the major xanthone; α-mangostin was found to be 10-fold less active than γ-mangostin when minimum inhibitory concentration values were compared.

Isolation and Pathogenicity of Streptococcus iniae in Cultured Red Hybrid Tilapia in Malaysia.

This study describes the isolation and pathogenicity of Streptococcus iniae in cultured red hybrid tilapia (Nile Tilapia Oreochromis niloticus × Mozambique Tilapia O. mossambicus) in Malaysia. The isolated gram-positive S. iniae appeared punctiform, transparently white, catalase and oxidase negative and produced complete ß-hemolysis on blood agar, while a PCR assay resulted in the amplification of the 16 S rRNA gene and lactate oxidase encoded genes. The isolate was sensitive to tetracycline, vancomycin, and bacitracin but was resistant to streptomycin, ampicillin, penicillin, and erythromycin. Pathogenicity trials conducted in local red hybrid tilapia (mean ± SE = 20.00 ± 0.45 g) showed 90.0, 96.7, and 100.0% mortality within 14 d postinfection following intraperitoneal exposure to 104, 106, and 108 CFU/mL of the pathogen, respectively. The clinical signs included erratic swimming, lethargy, and inappetance at 6 h postinfection, while mortality was recorded at less than 24 h postinfection in all infected groups. The LD50-336 h of S. iniae against the red hybrid tilapia was 102 CFU/mL. The post mortem examinations revealed congested livers, kidneys, and spleens of the infected fish. This is the first report of S. iniae experimental infection in cultured red hybrid tilapia in Malaysia. Received January 20, 2017; accepted July 16, 2017.