Infection In Tilapia Research Articles

First case of Aeromonas schubertii infection in brackish water wild Nile tilapia, Oreochromis niloticus, in China

To identify and characterize the etiological agent causing tilapia (Oreochromis niloticus) mortality in a lagoon located in Haikou, China, four isolates, designated ASL-1, ASB-2, ASB-3 and ASS-4, were recovered from moribund fish. They were gram-negative, motile, short and rod-shaped. Sequencing of the 16S rRNA gene, as well as of the housekeeping genes-dnaJ, elastase (ela) and gyrase subunit beta (gyrB), strongly indicated that the four isolates were identical to Aeronomas schubertii. A virulence test showed that ASS-4 was the most virulent, and the lethal dose (LD50) of 7 days was 4.91 × 104 CFU/g fish by intraperitoneal (i.p.) injection. Different infection routes with ASS-4 induced different mortality rates. Acute mortalities were present after both i.p. and intramuscular (i.s.) injections. Very low mortalities were observed after oral exposure, and no mortality was observed after immersion. This suggested that the natural infection routes of A. schubertii in tilapia might be through damaged body surface and/or digestive tract. The histopathology of challenged fish included livers showing vacuolation, spleens with hemorrhaging and brains with swelling capillaries. Antibiotic sensitivity testing indicated that ASS-4 was susceptible to norfloxacin and rifampicin but resistant to 10 different antibiotics. This is the first report that A. schubertii infected brackish water wild fish. This is also the first investigation of the possible entry routes of A. schubertii in fish. These results will shed light on the pathogenicity of A. schubertii and will help prevent and control A. schubertii infection in tilapia.

Interaction of Group B Streptococcus sialylated capsular polysaccharides with host Siglec-like molecules dampens the inflammatory response in tilapia

Group B Streptococcus (GBS, S. agalactiae) infection in tilapia (Oreochromis niloticus) causes widespread death of this species and is a significant issue for the aquaculture industry. The major virulence factor for GBS is its sialylated capsular polysaccharides (CPs). These CPs interact with sialic acid-binding immunoglobulin-like lectins (Siglecs) on the host immune cells to regulate the downstream inflammatory response and evade detection. Previously, we cloned multiple Siglec-like molecules from an O. niloticus cDNA library, all of which were shown to interact with the sialylated CPs of GBS. In the present study, we investigated the effects of GBS infection on the expression of pro- and anti-inflammatory cytokines in O. niloticus as well as OnSiglec-like-transfected macrophage cells. Eukaryotic expression vectors containing full-length OnSiglec-1-like, -4b-like, -14-like were constructed and used to transfect RAW264 macrophages in vitro as well as live tilapia in vivo prior to GBS infection. The expression of the anti-inflammatory cytokine interleukin (IL)-10 and the pro-inflammatory cytokines tumor necrosis factor (TNF)-α, IL-6, and interferon (INF)-β were then analyzed by qPCR. Our results indicate that as infection progressed, IL-10 expression was significantly upregulated, while that of TNF-α and IL-6 were significantly downregulated in the OnSiglec-like-transfected cells. INF-β expression was also downregulated in cells transfected with OnSiglec-1-like and -4b-like, but was not significantly effected in OnSiglec-14-like-transfected cells. Notably, the magnitude of these cytokine expression changes was greatly decreased when a ΔneuA GBS mutant was used to infect the OnSiglec-1-like-transfected cells. In GBS-infected tilapia, IL-10 expression was significantly upregulated in all tissues, whereas INF-β expression in the spleen, kidney, and gills was significantly downregulated at 12 hpi. While the expression of TNF-α was slightly upregulated, this change was not significant. In GBS ΔneuA mutant-infected O. niloticus, IL-10 expression in all of the tissues was significantly lower than that observed for the wild-type GBS group, while TNF-α expression was higher in the mutant infected group. There was no significant difference in INF-β expression between the two groups. Taken together, sialylated CPs on GBS appear to interact with host OnSiglec-like molecules to transmit negative regulatory signals via enhanced anti-inflammatory cytokine IL-10 production and reduced pro-inflammatory cytokine production, ultimately leading to dampening of the host immune response. The results of this study further elucidate the molecular mechanism underlying GBS infection in tilapia and also provide candidate drug target molecules.

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.

Pathological analysis, detection of antigens, FasL expression analysis and leucocytes survival analysis in tilapia (Oreochromis niloticus) after infection with green fluorescent protein labeled Streptococcus agalactiae

The pathogenesis of Streptococcus agalactiae infection in tilapia has not been fully described. To understand this, we investigated the clinic-pathological features of acute experimental septicemia in tilapia (Oreochromis niloticus) after receiving an intra-peritoneal injection with S. agalactiae THN-1901GFP. Immunohistochemistry and sections of pathological tissues were used to estimate the level of damage in the head-kidney, liver, spleen and trunk-kidney. The expression of FasL was analyzed by western blotting in these samples based on their damage levels. Leucocytes were isolated from the head-kidney and incubated with S. agalactiae THN-1901GFP. Then, phagocytosis, programmed cell death and the expression of FasL were analyzed. The infected tissues showed varying degrees of necrosis and histolysis. The serous membrane of the intestine was dissolved by S. agalactiae THN-1901GFP. Antigens of S. agalactiae THN-1901GFP accumulated in different parts of the infected organs. In the head-kidney and spleen, the expression of FasL was up-regulated in parallel with increased tissue damage. After being incubated with S. agalactiae THN-1901GFP, the phagocytic capacity and ability were both very high and the expression of FasL remained high in leucocytes. S. agalactiae THN-1901GFP was able to survive for a long period of time after being engulfed by phagocytic cells. These findings offer insight into the pathogenesis of S. agalactiae infection in tilapia.

Development of a colloidal gold immunochromatographic strip for rapid detection of Streptococcus agalactiae in tilapia

A colloidal gold immunochromatographic strip was developed for rapid detection of Streptococcus agalactiae (S. agalactiae) infection in tilapia. The monoclonal antibodies (mAb) 4C12 and 3A9 were used to target S. agalactiae as colloidal gold-mAb conjugate and captured antibody, respectively. The colloidal gold immunochromatographic strip was assembled via routine procedures. Optimal pH and minimum antibody levels in the reaction system for gold colloidal-mAb 4C12 conjugation were pH 7.4 and 18μg/mL, respectively. Optimal concentrations of the captured antibody 3A9 and goat anti-mouse antibody were 0.6mg/mL and 2mg/mL, respectively. The sensitivity of the strip for detecting S. agalactiae was 1.5×105 colony forming units (CFU). No cross-reaction was observed with other commonly encountered bacteria, including Pseudomonas fluorescens, Aeromonas hydrophila, Vibrio anguillarum and Streptococcus iniae. The assay time for S. agalactiae was less than 15min. Tilapia samples artificially infected with S. agalactiae were tested using the newly developed strip. The results indicated that blood, brain, kidney, spleen, metanephros and intestine specimens of infected fish can be used for S. agalactiae detection. The validity of the strip was maintained for 6 months at 4°C. These findings suggested that the immunochromatographic strip was effective for spot and rapid detection of S. agalactiae infected tilapia.

Laboratory-controlled Challenges of Nile Tilapia (Oreochromis niloticus) with Streptococcus agalactiae: Comparisons between Immersion, Oral, Intracoelomic and Intramuscular Routes of Infection

Streptococcus agalactiae, the aetiological agent of streptococcosis in fish, is an important pathogen of cultured and wild fish worldwide. To gain a better understanding of the pathogenesis of streptococcosis in Nile tilapia (Oreochromis niloticus), and to identify the experimental route of infection that most closely mimics natural disease, fingerlings were challenged with S. agalactiae utilizing different delivery methods. Fingerlings were challenged via intracoelomic injection (ICinj), intramuscular injection (IMinj), orally or by immersion with serial dilutions of S. agalactiae. The dose lethal to 50% of test fish 15 days post challenge was 120 colony forming units (CFU)/fish after ICinj, and 105CFU/fish after IMinj. Acute mortalities were present in both groups, but were higher in the fish challenged by ICinj. Very low mortalities were observed in the fish challenged via oral or immersion routes. Post-mortem evaluation of survivors revealed classical lesions associated with fish streptococcosis, including granulomatous or lymphohistiocytic epicarditis, splenitis, meningitis, myocarditis, choroiditis and exophthalmia. The information obtained improves our understanding of the pathogenesis of streptococcosis in fish, and provides useful information regarding controlled experimental infections in tilapia challenged with S. agalactiae. Results from this study suggest that IMinj challenge methods are not only suitable to induce streptococcosis in tilapia, but they may be the preferred method to study the pathogenesis of the naturally-occurring disease in this species.

Detection of natural infection of infectious spleen and kidney necrosis virus in farmed tilapia by hydroxynapthol blue-loop-mediated isothermal amplification assay.

Infectious spleen and kidney necrosis virus (ISKNV) has recently been recognized as a causative agent of serious systemic disease in tilapia. Our objective was to establish a new colorimetric loop-mediated isothermal amplification (LAMP) assay with pre-addition of hydroxynapthol blue (blue-LAMP) to investigate ISKNV transmission in tilapia. The blue-LAMP, targeting a major capsid protein gene of ISKNV, was conducted at 65°C for 45min, allowing unaided visual detection of the pathogen based on colour change without cross-amplification of other known fish pathogens tested. Comparison of blue-LAMP and PCR assays revealed a higher detection level for blue-LAMP assay (41·33%) in a population of farmed tilapia infected with ISKNV. The investigation of ISKNV transmission pattern in farmed red tilapia using the blue-LAMP revealed a possible matroclinical form. The presence of ISKNV in the gonad samples was confirmed by insitu LAMP assay. Positive signals only appeared in ovarian follicles, and not in oocytes. Moreover, tissue tropism assay revealed that the brain was the main target organ in both farmed red tilapia (40%) and Nile tilapia (20%). The developed blue-LAMP assay has the potential to be used as a viable tool for screening covert and natural infections of ISKNV in tilapia. The evidence of vertical transmission of ISKNV infection in tilapia indicates the seriousness of this disease and will require a close attention and collaboration between tilapia hatcheries and disease experts in order to find a solution. The new blue-LAMP assay is a time-saving and economically viable detection tool, which allows unaided visual detection for ISKNV in tilapia, and it could be applicable for field applications. Evidence on the vertical transmission of ISKNV in farmed tilapia suggests a need for developing farm management practices to control the spread of virus in aquaculture industries.

Effects of dietary Lactobacillus plantarum and AHL lactonase on the control of Aeromonas hydrophila infectionin tilapia.

This study addressed the effects of dietary Lactobacillus plantarum or/and N‐acylated homoserine lactonase (AHL lactonase) on controlling Aeromonas hydrophila infection in juvenile hybrid tilapia (Oreochromis niloticus♀ × O. aureus ♂). Fish were fed Lb. plantarum subsp. plantarum strain JCM1149 (108 CFU/g feed) or/and AHL lactonase AIO6 (4 U/g) and were exposed to a chronic challenge of A. hydrophila NJ‐1 (105 cells/mL) for 14 days. Intestinal (foregut) alkaline phosphatase (IAP) activities were evaluated 1 day post challenge to reflect the resistance of fish against A. hydrophila infection. Parallel groups of fish with the same dietary assignments while unchallenged were also included to investigate the effect of dietary Lb. plantarum or/and AIO6 supplementation on gut health of tilapia. The results showed that IAP activity was significantly lower in fish fed with diets supplemented with Lb. plantarum JCM1149 or the combination of Lb. plantarum JCM1149 and AIO6, indicating enhanced resistance against A. hydrophila. Light microscopy and transmission electron microscopy images of foregut revealed damage caused by A. hydrophila NJ‐1, but dietary Lb. plantarum JCM1149 or/and AIO6 significantly alleviated the damages. Compared to the fish immersed in A. hydrophila NJ‐1, dietary Lb. plantarum JCM1149 or AIO6 could maintain the microvilli length in the foregut of tilapia. However, among the unchallenged groups of fish, the microvilli length in the foregut of tilapia fed AIO6 (singly or combination) and the microvilli density of tilapia fed AIO6 (singly) were significantly lower than those of the control, though the microvilli density in the combination treatment was significantly improved. Additionally, the dietary Lb. plantarum JCM1149 could down‐regulate the expression of stress‐related gene in the gut after the acute phase. In conclusion, the dietary Lb. plantarum JCM1149 is recommended to control the A. hydrophila infection in tilapia.

EPIDEMIOLOGY STUDY OF VIRAL NERVOUS NECROSIS (VNN) IN MALAYSIAN GROUPERS: SEQUENCE ANALYSIS STRATEGIES AND QUASISPECIES DETERMINANT’S

EPIDEMIOLOGY STUDY OF VIRAL NERVOUS NECROSIS (VNN) IN MALAYSIAN GROUPERS: SEQUENCE ANALYSIS STRATEGIES AND QUASISPECIES DETERMINANT’S

Treatment of Trichodina sp reduced load of Flavobacterium columnare and improved survival of hybrid tilapia

Bacterium Flavobacterium columnare and protozoan Trichodina spp are common pathogens of cultured fish. Studies of parasite–bacterium interaction show evidence that concurrent infections increase severity of some infectious diseases, especially bacterial diseases. The effect of parasite treatment on F. columnare infection in tilapia is currently unknown. This study evaluated whether treatment of Trichodina sp parasitized hybrid tilapia (Oreochromis niloticus×Oreochromis aureus) with formalin would improve fish survival and reduce F. columnare infection in fish after F. columnare exposure. Hybrid tilapia parasitized by Trichodina sp were divided into 3 treatment groups. The first group of fish received no parasite treatment. The second group of fish were bath treated with 150mgL−1 formalin for 1h. The third group of fish treated twice with 150mgL−1 formalin bath for 1h each at 2 day intervals. All fish were then exposed to F. columnare by immersion challenge. The tilapia not treated with formalin showed significantly higher mortality (37.5%) than those treated with formalin (≤16.7%) after exposure to F. columnare. Fish treated twice showed lower mortality (6.37%) than those treated only once (16.7%). The non-treated fish showed significantly higher load of F. columnare in gill, kidney and liver compared to those treated with formalin following exposure to F. columnare. The bacterial load of non-treated fish was 27075 genome equivalents per mg of gill tissue (GEs/mg), 12 fold higher than those treated once with formalin (2250 GEs/mg) or 39 fold higher than those treated twice with formalin (699 GEs/mg) after exposure to F. columnare. This study demonstrated that formalin treatment for Trichodina sp parasitism reduced bacterial infection as suggested by reduced loads of bacteria in fish tissues and subsequently decreased fish mortality.

β-Defensin in Nile tilapia (Oreochromis niloticus): Sequence, tissue expression, and anti-bacterial activity of synthetic peptides

Beta-defensins (β-defensins) are small cationic amphiphilic peptides that are widely distributed in plants, insects, and vertebrates, and are important for their antimicrobial properties. In this study, the β-defensin (Onβ-defensin) gene of the Nile tilapia (Oreochromis niloticus) was cloned from spleen tissue. Onβ-defensin has a genomic DNA sequence of 674bp and produces a cDNA of 454bp. Sequence alignments showed that Onβ-defensin contains three exons and two introns. Sequence analysis of the cDNA identified an open reading frame of 201bp, encoding 66 amino acids. Bioinformatic analysis showed that Onβ-defensin encodes a cytoplasmic protein molecule containing a signal peptide. The deduced amino acid sequence of this peptide contains six conserved cysteine residues and two conserved glycine residues, and shows 81.82% and 78.33% sequence similarities with β-defensin-1 of fugu (Takifugu rubripes) and rainbow trout (Oncorhynchus mykiss), respectively. Real-time quantitative PCR showed that the level of Onβ-defensin expression was highest in the skin (307.1-fold), followed by the spleen (77.3-fold), kidney (17.8-fold), and muscle (16.5-fold) compared to controls. By contrast, low levels of expression were found in the liver, heart, intestine, stomach, and gill (<3.0-fold). Artificial infection of tilapia with Streptococcus agalactiae (group B streptococcus [GBS] strain) resulted in a significantly upregulated expression of Onβ-defensin in the skin, muscle, kidney, and gill. In vitro antimicrobial experiments showed that a synthetic Onβ-defensin polypeptide had a certain degree of inhibitory effect on the growth of Escherichia coli DH5α and S. agalactiae. The results indicate that Onβ-defensin plays a role in immune responses that suppress or kill pathogens.

Use of Cassia alata aqueous extract as a bath treatment to control Pseudomonas anguilliseptica infection in tilapia (Oreochromis niloticus)

The aqueous extracts of six plants, Andrographis paniculata, Cassia alata, Centella asiatica, Garcinia mangostana, Punica granatum and Psidium guajava, were investigated for their antimicrobial activity and mode of action against Pseudomonas anguilliseptica, an important fish pathogenic bacterium, which is responsible for economic losses in aquaculture worldwide. Among the tested plant extracts, the C. alata aqueous extract had the strongest inhibitory effect and exhibited a bactericidal mode of action against the pathogenic bacterium. When an infection of tilapia (Oreochromis niloticus) with P. anguilliseptica was induced by intraperitoneal, the median lethal dose (LD50) was determined to be 1.59 x 105 CFU/ml. For the in vivo trial, four different concentrations (25, 50, 75 and 100 ppm) of C. alata aqueous extract were used as bath treatment to remedy the infection. The effect of the extract on the infection was dose-dependent and an extract with the concentration of 100 ppm eliminated mortality of the infected fish without producing any adverse effects on the animals. This study suggests that C. alata aqueous extract has the potential to control fish disease caused by P. anguilliseptica.

Evaluation of the effects of essential oil extracted from sweet orange peel (Citrus sinensis) on growth rate of tilapia (Oreochromis mossambicus) and possible disease resistance against Streptococcus iniae

Abstract The study was performed to determine the effect of dietary essential oil (citrus EO) extracted from sweet orange peel (Citrus sinensis) on growth performance, blood parameters and resistance against the Streptococcus iniae in Mozambique tilapia (Oreochromis mossambicus). Fish were divided into 4 groups and fed for 90 days with four experimental diets (3 supplemented diets with 0.1%, 0.3%, and 0.5% of citrus EO and a control group). Then the main immune parameters such as lysozyme and myeloperoxidase activity, hematological and biochemical variables (i.e., hemoglobin, hematocrit levels, erythrocyte indices, serum total protein, glucose, albumin, globulin, cholesterol and triglyceride) were investigated. Results of this study showed that for tilapia fed with citrus EO all parameters were significantly higher than the control group. Moreover, addition of citrus EO into diets reduced fish mortality after S. iniae infection. It can be concluded that citrus EO can act as a growth promoter, increase immunity and also improve disease resistance to S. iniae infection in tilapia. Thus it can be used as an antibiotics replacer for controlling diseases in tilapia feed.

Identification of a virulence-related surface protein XF in piscine Streptococcus agalactiae by pre-absorbed immunoproteomics.

BackgroundSince 2009, large-scale Streptococcus agalactiae infections have broken out in cultured tilapia farms in China, resulting in considerable economic losses. Screening of the surface proteins is required to identify virulence factors or protective antigens involved in piscine S.agalactiae infections in tilapia. Pre-absorbed immunoproteomics method (PAIM) is a useful method previously established in our laboratory for identifying bacterial surface proteins.ResultsA serine-rich repeat protein family 1 (Srr-1), designated XF, was identified by PAIM in piscine S. agalactiae isolate GD201008-001. To investigate the role of XF in the pathogenesis of piscine S. agalactiae, an isogenic xf mutant strain (Δxf) and a complemented strain (CΔxf) were successfully constructed. The Δxf mutant and CΔxf showed no significant differences in growth characteristics and adherence to HEp-2 cells compared with the wild-type strain. However the 50% lethal dose of Δxf was increased (4-fold) compared with that of the parental strain in a zebrafish infection model.ConclusionsThe findings demonstrated that XF is a virulence-related, highly immunoreactive surface protein and is involved in the pathogenicity of S. agalactiae infections in fish.Electronic supplementary materialThe online version of this article (doi:10.1186/s12917-014-0259-7) contains supplementary material, which is available to authorized users.

A recombinant truncated surface immunogenic protein (tSip) plus adjuvant FIA confers active protection against Group B streptococcus infection in tilapia

PurposeTilapia is an important agricultural fish that has been plagued by Group B streptococcus (GBS) infections in recent years, some of them severe. It is well-known that surface immunogenicity protein (Sip) is an effective vaccine against GBS. Experimental designSince Sip was not expressed in either E. coli BL21 or E. coli Rosetta, we removed the N-terminal signal peptide and LysM of the virus to produce purified truncated Sip (tSip11tSip: truncated Sip.), which multiplied easily in an E. coli host. The antibody's ability to recognize and combine with GBS was determined by Western-blot and specific staining in vitro. The relative percentage of survival (RPS), antibody titers, bacterial recovery, and pathologic morphology were monitored in vivo to evaluate the immune effects. Freund's incomplete adjuvant (FIA) plus tSip and aluminum hydroxide gel (AH) plus tSip were also evaluated. ResultsIt revealed that tSip mixed with FIA was an effective vaccine against GBS in tilapia, while AH is toxic to tilapia.

Bacterial distribution and tissue targets following experimental Edwardsiella ictaluri infection in Nile tilapia Oreochromis niloticus

Edwardsiella ictaluri, a Gram-negative enteric bacterium, is the known etiological agent of enteric septicemia of catfish. In the last few years, different strains have been implicated as the causative agent of mortality events in cultured fish, including Nile tilapia Oreochromis niloticus L. Due to the emergent nature of edwardsiellosis in non-ictalurid fish, little is known about the dynamics of E. ictaluri infection in tilapia. The purpose of this study was to gain a better understanding of the pathogenesis of edwardsiellosis in tilapia by determining the median lethal and infective doses, tissue targets of infection, rate of bacterial dissemination, and the specific tissue response to E. ictaluri following an immersion challenge with bacterial strains recovered from outbreak events in tilapia. In addition to histopathology assessment, the bacterial burdens in several tissues of infected fish were determined over a 2 wk course of infection using quantitative real-time PCR (qPCR). The collected data suggest the cutaneous and oral routes as the main ports of entry for the organism, which later spreads hematogenously throughout the body. Even though histopathological assessment of infected fish revealed involvement of a wide range of tissues, the severity of the necrotizing and granulomatous lesions in the spleen and head kidney, with concomitant high levels of bacterial DNA in these organs determined by qPCR, identifies them as the main targets of infection.

Oral administration of bovine lactoferrin inhibits bacterial infection in tilapia and elevates survival after bacterial infection: an examination of its immune-modulating properties

It was previously reported that the oral administration of lactoferrin (LF) provides antimicrobial activity in animals against bacterial and viral infections and is involved in immunomodulatory properties. In this report, a hybrid strain of Oreochromis nilotica (male) × O. mossambicus (female) was fed homemade diets with or without supplementation with 10, 50, 100, and 150 mg bovine LF g−1 feed for 60 days. After dietary treatment, the experimental fish were infected with Streptococcus agalactiae. LF supplementation resulted in a significantly higher survival rate and suppression of bacterial growth at 24–96 h in the liver, spleen, kidneys, eyes, and gills. A reduction in peroxidase activity was followed by a similar reduction in the peroxidase content of leukocytes at 24 h as analyzed by spectrophotometry. Respiratory burst (RB) activity was detected regardless of the time at which LF was administered to fish in relation to the bacterial infection. A beneficial effect of LF on RBs was also detected before bacterial challenge (with 100 mg LF/g) and 24 h after bacterial challenge with 150 mg/g. The results obtained validate LF’s beneficial effects on RBs by phagocytes in tilapia, which was only shown at 48 h after supplementation with 100 mg bovine LF g−1 feed after the bacterial infection. Moreover, after oral administration of LF, it was detected in the mucosa of the small intestines of tilapia. In conclusion, we demonstrate a reduction in fish mortality after the oral administration of LF, and we examined its immunomodulatory properties in tilapia.

Novel brain lesions caused by Edwardsiella tarda in a red tilapia (Oreochromis spp.)

The histological lesions caused by Edwardsiella tarda in a variety of fish species, including tilapia, have been well characterized. There are apparent differences in the type of inflammatory response manifested by these different species, which may be due to the fish species itself, the phase of infection, or the virulence factors produced by different strains of E. tarda. In catfish, systemic abscesses involving muscles of the flank or caudal peduncle are the most common lesions. By contrast, infection in tilapia and red sea bream is more likely to be associated with granulomatous inflammation. Necrotic meningitis, encephalitis, and vasculitis with fibrinoid necrosis of the blood vessels walls, as well as the formation of a plaque-like structure in the brain, are described in the current study. The presence of E. tarda was confirmed by microbiological isolation and a positive nested polymerase chain reaction in paraffin wax-embedded tilapia tissues.

Ulcerative Aeromonas Infections in Tilapia (Cichlidae: Tilapiini) from Mtera Hydropower Dam, Tanzania

Ulcerative Aeromonas Infections in Tilapia (Cichlidae: Tilapiini) from Mtera Hydropower Dam, Tanzania

Effects of hot-water extract of Toona sinensis on immune response and resistance to Aeromonas hydrophila in Oreochromis mossambicus

Respiratory burst, lysozyme and phagocytic activities, and immunoglobulin levels in response to the pathogen Aeromonas hydrophila were examined in tilapia ( Oreochromis mossanbicus, 10.65 ± 2.5 g) injected individually with hot-water extract of Toona sinensis at 4 or 8 μg g −1. Tilapia receiving the hot-water extract of T. sinensis at either dose had significantly increased respiratory burst, phagocytic activity and lysozyme activity towards A. hydrophila by 1 and 2 days post injection. No significant differences in total immunoglobulin levels were observed among the tilapia that received the two different doses of hot-water extract of T. sinensis at 4 and 8 μg g −1. In another experiment, a Tilapia that had been injected with hot-water extract of T. sinensis was challenged with A. hydrophila at 5 × 10 7 colony-forming units (cfu) fish −1. The survival of tilapia that received the hot-water extract of T. sinensis at 8 μg g −1 was significantly higher than fish that received phosphate buffered saline and the control fish after 2 days, and at the termination of the experiment (7 days after the challenge). It was concluded that the hot-water extract of T. sinensis at 8 μg g −1 or less had increased the immune response and resistance to A. hydrophila infection in tilapia.