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

A first report of Streptococcus iniae infection of the spotted sea bass (Lateolabrax maculates)

This study marks the first occasion that Streptococcus iniae has been isolated, identified, and characterized as the causative pathogen in spotted sea bass (Lateolabrax maculates). Infected fish exhibited a range of external symptoms, including scale loss, bleeding from the jaw, anus, and tail, among other signs, as well as internal manifestations such as congested liver, splenomegaly, branchial anemia, yellow fat syndrome, and intestinal edema. Notably, exophthalmia and meningoencephalitis-typical symptoms associated with previous S. iniae infections-were not observed. A predominant bacterial isolate (designated 10S01) was recovered from the pure culture of spleen of a diseased spotted sea bass in Zhuhai, China. The strain was then subjected to Gram staining, biochemical profiling, and molecular confirmation through 16S rRNA and gyrB gene, corroborating its identity as S. iniae. Pathogenicity was assessed by intraperitoneal injection challenge in spotted sea bass weighing approximately 13 g/fish, revealing a LD50 of 74 cfu/g-fish. The 10S01 strain demonstrated the ability to colonize various organs, including the spleen, liver, kidney, and brain, with a relatively higher affinity for the spleen. Furthermore, antimicrobial susceptibility testing indicated that the 10S01 strain was sensitive to 14 tested antibiotics, particularly chloramphenicol, ciprofloxacin, clarithromycin, florfenicol, ofloxacin, rifampicin, and trimethoprim/sulfamethoxazole, highlighting these as preferred treatments for S. iniae infections in spotted sea bass. These findings contribute significantly to our understanding of S. iniae pathogenesis and inform the prompt and appropriate antibiotic treatment of S. iniae infections.

Cellulitis and bacteremia caused by the fish pathogen,Streptococcus iniae, in an immunocompromised patient: Case report and mini-review of zoonotic disease, lab identification, and antimicrobial susceptibility

Streptococcus iniae is a fish pathogen that can also infect mammals including dolphins and humans. Its prevalence in farmed fish, particularly tilapia, provides potential for zoonotic infections, as documented by multiple case reports. Systematic clinical data beyond cellulitis for S. iniae infection in humans, including antimicrobial susceptibility data, are unfortunately rare. Here, we present a case of cellulitis progressing to bacteremia caused by Streptococcus iniae in a functionally immunocompromised patient based on CDK4/CDK6 inhibitor and endocrine therapy, and we discuss risk factors, identification, and antimicrobial susceptibility of this rare pathogen.

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.

Immunogenicity and Efficacy of a Feed-Based Bivalent Vaccine against Streptococcosis and Motile Aeromonad Septicemia in Red Hybrid Tilapia (Oreochromis sp.)

Streptococcosis and motile Aeromonad septicemia (MAS) are the main bacterial diseases in tilapia culture worldwide, causing significant economic losses. Vaccination is an effective method of preventing diseases and contributes to economic sustainability. This study investigated the immuno-protective efficacy of a newly developed feed-based bivalent vaccine against streptococcosis and MAS in red hybrid tilapia. The feed-based bivalent vaccine pellet was developed by incorporating the formalin-killed S. agalactiae and A. hydrophila antigens into a commercial feed pellet with palm oil as the adjuvant. The bivalent vaccine was subjected to feed quality analyses. For immunological analyses, 900 fish (12.94 ± 0.46 g) were divided into two treatment groups in triplicate. Fish in Group 1 were unvaccinated (control), while those in Group 2 were vaccinated with the bivalent vaccine. The bivalent vaccine was delivered orally at 5% of the fish's body weight for three consecutive days on week 0, followed by boosters on weeks 2 and 6. Lysozyme and enzyme-linked immunosorbent assays (ELISAs) on serum, gut lavage, and skin mucus were performed every week for 16 weeks. Lysozyme activity in vaccinated fish was significantly (p ≤ 0.05) higher than in unvaccinated fish following vaccination. Similarly, the IgM antibody levels of vaccinated fish were significantly (p ≤ 0.05) higher after vaccination. The bivalent vaccine provided high protective efficacy against S. agalactiae (80.00 ± 10.00%) and A. hydrophila (90.00 ± 10.00%) and partial cross-protective efficacy against S. iniae (63.33 ± 5.77%) and A. veronii (60.00 ± 10.00%). During the challenge test, fewer clinical and gross lesions were observed in vaccinated fish compared with unvaccinated fish. Histopathological assessment showed less severe pathological changes in selected organs than the unvaccinated fish. This study showed that vaccination with a feed-based bivalent vaccine improves immunological responses in red hybrid tilapia, and thus protects against streptococcosis and MAS.

Chicken Enterococcus faecalis-induced immunoglobulin Y as a prophylactic and therapeutic agent against streptococcosis in red tilapia (Oreochromis hybrid)

Background and Aim

Streptococcosis is a common bacterial disease in red tilapia, in which Enterococcus faecalis infection has not been widely reported. This study aimed to evaluate the efficacy of pellets that contain chicken E. faecalis-induced immunoglobulin Y (IgY) to treat and prevent streptococcosis in red tilapia.

Materials and Methods

We conducted a 28-day study for immunoprophylaxis and immunotherapy, each using four groups with two replications: Healthy control fish (KS), non-IgY pellets (PA and TA), pellets with 25% egg yolk containing E. faecalis-induced IgY (PB and TB), and pellets with 50% egg yolk containing E. faecalis-induced IgY(PC and TC). Indirect enzyme-linked immunosorbent assay was performed on prototype pellets produced with an IgY suspension at 1.63 mg/mL as the standard optical density curve. For the immunoprophylaxis study, pellets of 3% of the average body weight of the experimental fish (0.50 g per fish per day) were given daily until day 14 before the challenge test with E. faecalis (2.1 × 10⁹ Colony-forming unit/mL peroral) on day 15. The data from the observation period on days 15-28 were analyzed. For the immunotherapy study, pellets of 3% of the average body weight (0.50 g per fish per day) were given daily for 21 days (days 8-28) 7 day spost-infection. The data from the immunotherapy study were collected during the observation period on days 8-28. Statistical analysis was performed on non-specific immune variables: Total leukocytes, monocytes, lymphocytes, neutrophils, phagocytic activity, and macrophage capacity; and the semi-quantitative distribution of melanomacrophage centers (MMCs) in the lymphoid organs, such as spleen and liver. Photomacrographic data were analyzed descriptively and qualitatively by comparing the healing process and clinical signs found between experiments in the immunotherapy study.

Results

The pellet with 50% egg yolk with an IgY at 2.43 mg/g pellet, 3% of body weight once daily, was the best formula on experimental fish. The administration of this formulation can also increase non-specific immunity and the distribution of MMCs in the spleen and liver with a survival rate of 55% for 14 days of challenge period in the immunoprophylaxis study and 70% for 21 days of therapy period in the immunotherapy study.

Conclusion

Immunoglobulin Y can be a prophylactic and therapeutic agent against streptococcal infections caused E. faecalis in red tilapia with an optimum dosage of 2.43 mg/g pellet.

Effect of an Oral Bivalent Vaccine on Immune Response and Immune Gene Profiling in Vaccinated Red Tilapia (Oreochromis spp.) during Infections with Streptococcus iniae and Aeromonas hydrophila

Streptococcosis and aeromonasis inflicted by Streptococcus iniae and Aeromonas hydrophila, respectively, have affected tilapia industries worldwide. In this study, we investigated antibody responses and explored the mechanisms of protection rendered by an oral bivalent vaccine in red tilapia following challenges with S. iniae and A. hydrophila. The results of specific IgM antibody response revealed that the IgM titers against S. iniae and A. hydrophila in the bivalent incorporated (BI) vaccine group were significantly higher (p < 0.05) than those in the bivalent spray (BS) vaccine fish and unvaccinated control fish throughout the experiment. Real-time qPCR results also showed that the gene expression of CD4, MHC-I, MHC-II, IgT, C-type lysozyme, IL-1β, TNF-α, and TGF-β remained significantly higher (p < 0.05) than that of the controls between 24 and 72 h post-infection (hpi) in both mucosal (hindgut) and systemic (spleen and head−kidney) organs of BI vaccinated fish. Furthermore, the highest relative expression of the TGF-β, C-type lysozyme, and IgT genes in the BI vaccinated group was observed in the challenged fish’s spleen (8.8-fold), head kidney (4.4-fold), and hindgut (19.7-fold) tissues, respectively. The present study suggests that the bivalent incorporated (BI) vaccine could effectively improve the immune function and activate both humoral and cell-mediated immunities in vaccinated red tilapia following the bacterial challenges.

The Antibacterial Activity of Thymol Against Drug-Resistant Streptococcus iniae and Its Protective Effect on Channel Catfish (Ictalurus punctatus)

Streptococcus iniae is a zoonotic pathogen, which seriously threatens aquaculture and human health worldwide. Antibiotics are the preferred way to treat S. iniae infection. However, the unreasonable use of antibiotics leads to the enhancement of bacterial resistance, which is not conducive to the prevention and treatment of this disease. Therefore, it is urgent to find new efficient and environmentally friendly antibacterial agents to replace traditional antibiotics. In this study, the antibacterial activity and potential mechanism of thymol against S. iniae were evaluated by electron microscopy, lactate dehydrogenase, DNA and protein leakage and transcriptomic analysis. Thymol exhibited potent antibacterial activity against S. iniae in vitro, and the MIC and MBC were 128 and 256μg/mL, respectively. SEM and TEM images showed that the cell membrane and cell wall were damaged, and the cells were abnormally enlarged and divided. 2MIC thymol disrupted the integrity of cell walls and membranes, resulting in the release of intracellular macromolecules including nucleotides, proteins and inorganic ions. The results of transcriptomic analysis indicated that thymol interfered with energy metabolism and membrane transport, affected DNA replication, repair and transcription in S. iniae. In vivo studies showed that thymol had a protective effect on experimental S. iniae infection in channel catfish. It could reduce the cumulative mortality of channel catfish and the number of S. iniae colonization in tissues, and increase the activities of non-specific immune enzymes in serum, including catalase, superoxide dismutase, lysozyme and acid phosphatase. Taken together, these findings suggested that thymol may be a candidate plant agent to replace traditional antibiotics for the prevention and treatment of S. iniae infection.

Probiotic Bacillus safensis NPUST1 Administration Improves Growth Performance, Gut Microbiota, and Innate Immunity against Streptococcus iniae in Nile tilapia (Oreochromis niloticus)

Probiotics are considered ecofriendly alternatives to antibiotics as immunostimulants against pathogen infections in aquaculture. In the present study, protease-, amylase-, cellulase-, and xylanase-producing Bacillus safensis NPUST1 were isolated from the gut of Nile tilapia, and the beneficial effects of B. safensis NPUST1 on growth, innate immunity, disease resistance and gut microbiota in Nile tilapia were evaluated by feeding tilapia a basal diet or basal diet containing 105 and 106-107 CFU/g for 8 weeks. The results showed that the weight gain, feed efficiency and specific growth rate were significantly increased in tilapia fed a diet containing 106 CFU/g and 107 CFU/g B. safensis NPUST1. Intestinal digestive enzymes, including protease, amylase and lipase, and hepatic mRNA expression of glucose metabolism and growth-related genes, such as GK, G6Pase, GHR and IGF-1, were also significantly increased in the 106 CFU/g and 107 CFU/g B. safensis NPUST1 treated groups. Immune parameters such as phagocytic activity, respiratory burst and superoxide dismutase activity in head kidney leukocytes, serum lysozyme, and the mRNA expression of IL-1β, IL-8, TNF-α and lysozyme genes were significantly induced in the head kidney and spleen of 106 CFU/g and 107 CFU/g B. safensis NPUST1 treated fish. The cumulative survival rate was significantly increased in fish fed a diet containing 106 CFU/g and 107 CFU/g B. safensis NPUST1 after challenge with Streptococcus iniae. Dietary supplementation with B. safensis NPUST1 improves the gut microbiota of Nile tilapia, which increases the abundance of potential probiotics and reduces the abundance of pathogenic pathogens. The present study is the first to report the use of B. safensis as a potential probiotic in aquaculture, and a diet containing 106 CFU/g B. safensis NPUST1 is adequate for providing beneficial effects on growth performance and health status in tilapia.

Fatal Streptococcus iniae Infection in a Juvenile Free-Ranging Short-Beaked Common Dolphin (Delphinus delphis)

Simple Summary

Streptococcus iniae (S. iniae) is a significant aquatic bacterial pathogen that has caused devastating losses to wild and cultured fish populations worldwide and is an important zoonotic pathogen in humans. Previously reported in captive dolphins only, this case report describes S. iniae associated infection and mortality in a free-ranging short-beaked common dolphin (Delphinus delphis). Unreported previously in wild marine mammals, its detection highlights a need for further investigation into the epidemiology of S. iniae to better understand the risks for wild marine mammal populations and potential transmission cycles between marine mammals, humans and wild and intensive fish populations.

Abstract

Streptococcus iniae (S. iniae) is a significant aquatic pathogen of farmed fish species, important zoonotic pathogen, and reported cause of disease in captive Amazon River dolphins (Inia geoffrensis) and a bottlenose dolphin (Tursiops truncatus). Here we report S. iniae as the cause of subcutaneous abscesses, sepsis and mortality in a juvenile free-ranging short-beaked common dolphin (Delphinus delphis) found deceased on a metropolitan Australian beach. Body surfaces were covered by multifocal, depressed, deep, irregular cutaneous ulcerations, which microscopically were characterised by ruptured subcutaneous abscesses with intralesional cocci. Routine microbiological investigations revealed a heavy growth of beta-haemolytic Streptococcus sp. identified as Streptococcus iniae in skin lesions as well as from heart blood, the latter supportive of sepsis. Tissues were negative for cetacean morbillivirus and no other disease processes were identified. S. iniae has not been reported in free-ranging marine mammals, nor in Australian delphinids, previously. More notably a pathogen of captive animals, this case report identifies S. iniae as a pathogen of wild dolphins also. In addition to expanding the host reservoir of a significant zoonotic pathogen, determining the source of infection as well as possible consequences for other marine mammals and wild and intensive fish stocks warrants further investigations.

Immuno-protective efficiency of feed-based whole-cell inactivated bivalent vaccine against Streptococcus and Aeromonas infections in red hybrid tilapia (Oreochromis niloticus × Oreochromis mossambicus)

Streptococcosis and motile aeromonad septicemia (MAS) are well-known diseases in tilapia culture, which cause mass mortality with significant economic losses. The development of feed-based bivalent vaccines in controlling these diseases has been initiated, however, the mechanisms of immunities and cross-protection in fish remain unclear. This study was conducted to assess the immuno-protective as well as the cross-protective efficacy of a newly developed feed-based bivalent vaccine against Streptococcus and Aeromonas infections in red hybrid tilapia. A total of five groups of fish were vaccinated orally through two different techniques; bivalent vaccine (inactivated Streptococcus iniae and Aeromonas hydrophila) sprayed on feed pellets (BS group); bivalent vaccine (inactivated S. iniae and A. hydrophila) incorporated in feed (BI group); monovalent inactivated S. iniae and A. hydrophila vaccine separately incorporated into feed as monovalent S. iniae (MS group) and monovalent A. hydrophila (MA group); and control group (without vaccine). The feed-based vaccine was delivered orally at 5% of body weight for five consecutive days. The booster doses were given in the same manner on weeks 2 and 6. Serum and skin mucus samples were collected to assess the IgM responses using indirect ELISA. The first administration of the feed-based vaccine stimulated the IgM levels that lasted until week 3, while the second booster ensured that the IgM levels remained high for a period of 16 weeks in the BI, MS and MA groups. The BI group developed a strong and significantly (P < 0.05) higher systemic and mucosal IgM responses against both S. iniae and A. hydrophila and also cross-protective antigen S. agalactiae and A. veronii compared to the BS and control groups. Quantitative real-time PCR results also showed that the relative expressions of IL-8, INF-γ and IgM in the BI immunized fish spleen, head kidney and hindgut exhibited various significant (P < 0.05) rising trends following both the vaccination and the challenge phase. On weeks 10, all fish were challenged through the intraperitoneal route, where relative percent survivals (RPS) of 82.22 ± 3.85% when challenged with S. iniae, 77.78 ± 3.85% when challenged with A. hydrophila and 77.78 ± 3.85% when co-challenged with both S. iniae and A. hydrophila were observed in the BI group, which were significantly higher (P < 0.05) compared to the other groups. The BI group also showed significantly (P < 0.05) higher partial cross-protections following challenges with S. agalactiae (RPS at 60.00 ± 6.67%) and A. veronii (RPS at 57.78 ± 7.70%). This study demonstrated that immunization with feed-based BI vaccine elicited immune responses that were capable of protecting red hybrid tilapia against streptococcosis and MAS.

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.

Streptococcal Infections in Marine Mammals

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

Efficacy of Feed-Based Formalin-Killed Vaccine of Streptococcus iniae Stimulates the Gut-Associated Lymphoid Tissues and Immune Response of Red Hybrid Tilapia

Red hybrid tilapia were fed a formalin-killed oral Streptococcus iniae vaccine (FKV) in the present study was assessed. Three hundred Red hybrid tilapia 80 ± 10 g were divided into five groups (1A, 1B, 2A, 2B, and Cx), each consisting of 60 fish. Fish from Groups 1A, 1B, 2A, and 2B were fed with FKV over different periods of administration, while Group 2B was the only group of fish to receive an oral booster vaccination on day 14- and 21-days post-vaccination (dpv). Group Cx was fed with normal pellets containing no vaccine as a control group. At four weeks post-vaccination (wpv), all fish were experimentally infected with S. iniae. Groups 2A and 2B had the lowest level of mortalities following vaccination (45% and 30%, respectively) compared to Groups 1A and 1B (80% and 55%, respectively), while the level of mortalities in Group Cx was 100%. All vaccinated groups showed a significant increase in anti-S. iniae IgM levels (p < 0.05) in serum, mucus, and gut-lavage, while Group Cx did not (p > 0.05) and all fish in this group died by five weeks post-infection. In conclusion, fish fed with the S. iniae FKV had a greater level of protection against S. iniae, with increased specific antibody response to the vaccine and there was also evidence of GALT stimulation by the vaccine.

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.

Development of fish vaccine in Southeast Asia: A challenge for the sustainability of SE Asia aquaculture

Southeast (SE) Asia plays an important role in global food security as this region has been regarded as one of the major producers of aquaculture product and, to date, freshwater fish accounted for one-third of the total aquaculture in SE Asia. The intensification of freshwater farming corresponding to increase of consumer demands has inevitably led to the emergence and re-emergence of diseases causing tremendous economic loss in the region. Nile tilapia (Oreochromis niloticus) and striped catfish (Pangasianodon hypophthalmus), the major freshwater fish species of SE Asia, have been reported susceptible to several bacterial pathogens, e.g. Streptococcus agalactiae, Edwardsiella ictalurid and Flavobacterium columnare. Since only a limited number of vaccines being registered and marketed, these pathogenic organisms still represent a severe threat to aquaculture industry in SE Asia. However, there is profound advancement in the understanding of disease epidemiology, pathogenic mechanisms, teleost mucosal immunity and vaccine delivery system over the last few years. This review aimed to summarize those recent findings which hopefully can provide novel insight into the future development of suitable vaccine and vaccination regime against bacterial infection in SE Asia region.

Haemato-immunological responses and effectiveness of feed-based bivalent vaccine against Streptococcus iniae and Aeromonas hydrophila infections in hybrid red tilapia (Oreochromis mossambicus × O. niloticus)

Background

Streptococcosis and Motile Aeromonad Septicemia (MAS) are important diseases of tilapia, Oreochromis spp. and causes huge economic losses in aquaculture globally. The feed-based vaccination may be an alternative to minimize major infectious diseases in tilapia. Thus, this study aims to evaluate the haemato-immunological responses and effectiveness of a newly developed feed-based killed bivalent vaccine against Streptococcus iniae and Aeromonas hydrophila in hybrid red tilapia. A total of 495 hybrid red tilapia of 61.23 ± 4.95 g were distributed into 5 groups (each with triplicate). The fish were immunized orally through bivalent (combined S. iniae and A. hydrophila) spray vaccine (BS group), bivalent formulate vaccine (BF group), monovalent S. iniae vaccine (MS group), monovalent A. hydrophila vaccine (MA group) and unvaccinated as a control group. The vaccine was orally administered on days 0, 14 and 42 applied feed-based bacterin at 5% body weight. The blood and spleen samples were collected from all groups on 7, 21 and 49 days post-vaccination, and also 96 h post-infection to assess their haemato-immune responses.

Results

Compared with the unvaccinated group, leukocyte, lymphocytes, monocytes, granulocytes counts in vaccinated groups were significantly (P < 0.05) increased on 21, 49 days post-vaccination and also 96 h post-infection, while erythrocytes, haemoglobin and haematocrit in vaccinated groups were significantly (P < 0.05) enhanced only 96 h post-infection. Additionally, the lysozyme and phagocytic activity and, serum antibody (IgM) were significantly higher (P < 0.05) against S. iniae and A. hydrophila in vaccinated groups compared to the unvaccinated group in the pre- and post-infection. Results from the challenge through co-infection with S. iniae and A. hydrophila showed the relative percent survival (RPS) in BF group was 76.67 ± 4.71%, which had the capacity to induce significant protection (P < 0.05) compared to others groups.

Conclusions

This study demonstrates the bivalent formulate (BF) group could elicit significant non-specific and specific immunological responses with higher protection in hybrid red tilapia. In addition, this newly developed feed-based bivalent vaccination can be a promising technique for effective and large scale fish immunization in the aquaculture industry.

Vaccination of Tilapia against Motile Aeromonas Septicemia: A Review

The production of tilapia Oreochromis spp. is rapidly growing throughout the world, but atypical motile aeromonad septicemia (MAS) is a current threat to the tilapia farming industry. The etiological agent of this disease is usually Aeromonas hydrophila. Mortality rates due to MAS are frequently high, resulting in a devastating negative impact on this industry worldwide; therefore, proper control measures regarding both prevention and treatment are necessary. Although vaccines against MAS for tilapia are available, their effectiveness is entirely dependent on the specific strain of problematic bacteria. Until now, whole-cell inactivated A. hydrophila vaccines for tilapia have exhibited the highest level of protection over live attenuated and recombinant vaccines. Among the various vaccine administration systems, only intraperitoneal (i.p.) injections of the A. hydrophila vaccine into tilapia were found to provide prominent immune protection. Vaccine efficacy was primarily measured by using the i.p. injection challenge model and estimating the relative percent survival of the immunized tilapia. Freund's incomplete adjuvant showed to be the most effective for tilapia MAS vaccines. In this review, multiple factors that directly or indirectly influence the efficacy of MAS vaccines for tilapia (adjuvants, challenge models, immunization doses and duration, and size of vaccinated fish) are discussed.

Phenotypic and genotypic characterization of Streptococcus spp. isolated from tilapia (Oreochromis spp.) cultured in river-based cage and earthen ponds in Northern Thailand

Streptococcus spp. are major pathogenic bacteria associated with massive mortality in tilapia. This study investigated the phenotypic and genotypic characterization of Streptococcus agalactiae (GBS) and Streptococcus iniae (S. iniae) isolated from tilapia in river-based floating cage and earthen pond farms in northern Thailand. Isolates were identified by biochemical and molecular analyses. Capsular typing, enterobacterial repetitive intergenic consensus polymerase chain reaction and multilocus sequence typing were performed to investigate the genetic relatedness. Six and one isolates were confirmed as GBS and S. iniae, respectively. All Streptococcus spp. isolates were obtained from 4 river-based cage farms (4/33), while samples collected from earthen pond farms (N = 28) were negative for streptococcosis. All GBS with serotype Ⅲ and sequence type (ST) 283 was observed. The β-haemolytic GBS isolates were resistant to five antimicrobials, while the S. iniae was susceptible to all antimicrobials. This study indicates both GBS and S. iniae are the major bacterial pathogens responsible for streptococcosis infection in farmed tilapia of northern Thailand with GBS as dominant species. This survey highlights that the river-based cage farms seriously impact on the healthy development of the tilapia industry.

Efficacy of dietary Nano-selenium on growth, immune response, antioxidant, transcriptomic profile and resistance of Nile tilapia, Oreochromis niloticus against Streptococcus iniae infection

As recently applicable, there are few studies on the impact of using nano-selenium (nano-Se) on varied fish species. Where nothing reachable focused on its impact on tilapias so, the present analysis evaluated the efficacy of using nano-Se in tilapias on immune response, antioxidant defense compared by conventional Se form. 480 O. niloticus fingerlings were haphazardly grouped firstly into three groups with four replicates of each. The control one (CT) was fed on a basal diet. The second and third one supplemented with 0.7 mg/kg^-1 Se and nano-Se respectively for ten weeks. At the start day of the ninth week, two replicates from each group were injected by Streptococcus iniae where, the remaining replicates stand without challenge. Enhancement of growth performance measurements were noted in nano-Se compared to Se or CT groups. Existed anemia in S. iniae tilapias became alleviated by using nano-Se that also, improves the alteration of leucogram induced by challenge. Elevation of aminotransferases, alkaline phosphatase, lactate dehydrogenase (ALT, AST, ALP and LDH) and creatinine in Se and CT challenged replicates that seemed nearly normal by using nano-Se. Usage of nano-Se showed more powerful antioxidant activities than Se. There were an expansion of immunoglobulin M, lysozymes, glutathione peroxidase, nitric oxide, superoxide dismutase and catalase (IgM, LYZ, GPx, NO, SOD, CAT) and their related gene expression in nano-Se with contrast in Se or CT challenged groups. Nile tilapias challenged by S. iniae disclosed substantial expansion in the percentage of mortality in CT challenged fish (93.33%), followed by the group supplemented with Se (73.33%), whereas the lowermost one at fish supplemented by nano-Se (26.66%). The mortalities have been stopped from the 5^th, 12^th and 14^th days in, nano-Se, Se and CT respectively. It can be concluded that using of Se 0.7 mg/kg^-1induce immunosuppressive, antioxidant, liver and kidneys negative impact on tilapias where the same dose from nano-Se was more potent immunomodulating and antioxidant. Also it is attend in counteracting the serious impact induced by S. iniae challenge.

Dietary administration of probiotic Paenibacillus ehimensis NPUST1 with bacteriocin-like activity improves growth performance and immunity against Aeromonas hydrophila and Streptococcus iniae in Nile tilapia (Oreochromis niloticus)

Bacteria-induced diseases are a major cause of mortality in aquaculture. Probiotics have commonly been used to replace antibiotics for prophylactic biocontrol in aquaculture. In the present study, Paenibacillus ehimensis NPUST1 was isolated from a tilapia culture pond. This probiotic has bacteriocin-like activities against Aeromonas hydrophila and was characterized by biochemical analysis and 16S rDNA sequencing. The physiochemical properties of a crude extract of the bacteriocin-like substance revealed low pH and high thermal tolerance. The substance exhibited broad-spectrum antimicrobial activity against diverse aquatic pathogens, food spoilage, clinical pathogens, and plant pathogens. The effect of dietary supplementation with P. ehimensis NPUST1 was evaluated in regard to the growth of Nile tilapia (Oreochromis niloticus) and immunity against pathogenic infection. The results showed significantly increased weight gain (WG), feed conversion ratio (FCR), and feed efficiency (FE) in Nile tilapia fed P. ehimensis NPUST1 for 2 months compared with fish fed a control diet. When challenged with A. hydrophila and S. iniae, the fish fed P. ehimensis NPUST1 also exhibited a higher survival rate than fish fed the control diet. The immune parameters revealed that the P. ehimensis NPUST1-fed fish had significantly higher phagocytic activity, respiratory burst, and superoxide dismutase (SOD) of the head kidney leukocytes, as well as higher serum lysozyme activity and expression of cytokines TNF-α and IL-1β than the fish fed the control diet. These results indicate that dietary supplementation with P. ehimensis NPUST1 improved the growth performance, immunity, and disease resistance in Nile tilapia.