How to cite: Dong HT, Senapin S, Phiwsaiya K, Techatanakitarnan C, Dokladda K, Ruenwongsa P, Panijpan B (2018) Histopathology and culturable bacteria associated with “big belly” and “skin nodule” syndromes in ornamental Siamese fighting fish, Betta splendens. Microbial Pathogenesis. DOI: 10.1016/j.micpath.2018.06.005.
The Siamese fighting fish (Betta splendens) is one of the popular aquarium ornamental fish in the global trade. Large numbers of ornamental fish farmed in central Thailand suffered from two common syndromes; preliminarily named skin nodule syndrome (SNS) and big belly syndrome (BBS): they showed noticeable clinical signs of abnormal appearances resulting in depressed saleability. Since very few specifics are known about causative agents of these syndromes, this study aimed at investigating histopathological features and culturable bacteria associated with these fish infected in the process of farming. Histopathologically, SNS fish consistently exhibited necrosis and severe melanization in the muscles and multiple internal organs. Whereas BBS fish exhibited either typical granulomas or tissue damage associated with acid-fast stained bacteria and Gram negative bacteria, respectively. Six different Gram negative bacterial species were recovered from BBS fish while 23 bacterial species belonging to 14 genera were recovered from fish suffering from SNS. Most of the culturable bacteria are new to betta fish and some of them are known to be marine bacteria, suggesting possible entry route via a contaminated live feed, commercial Artemia shrimp. The true causative agents of these syndromes remain unclear. However, histopathological changes and existence of a wide range of bacteria associated with the naturally diseased fish suggest involvement of multiple bacterial infections.
Keywords: Betta splendens; Big belly syndrome; Culturable bacteria; Histopathology; Skin nodule syndrome
How to cite: Mata W, Putita C, Dong HT, Kayansamruaj P, Senapin S, Rodkhum C (2018) Quinolone-resistant phenotype of Flavobacterium columnare isolates harbored point mutations in both parC and gyrA but not in either gyrB or parE. Global Antimicrobial Resistance. doi: 10.1016/j.jgar.2018.05.014
Objective: Determination of mutations associated with quinolone-resistant (QR) phenotype of Flavobacterium columnare isolates.
Methods: The susceptibility of F. columnare isolates (n = 53) to 11 antibiotics, including 2 quinolones, was investigated using disk diffusion method. Oxolinic acid was subsequently chosen for minimum inhibitory concentration (MIC) assay. PCR and sequence analysis of four genes involved in the quinolone resistance-determining regions (QRDRs) from OA-resistant F. columnare compared to that of susceptible isolates were subsequently investigated.
Results: The result of disk diffusion assay revealed that the majority of isolates was susceptible to all tested antibiotics. However, 14 and 8 isolates were resistant to 2 quinolone antibiotics; oxolinic acid (OA) and nalidixic acid (NA), respectively. No multiple drug resistance was found in this study. MIC assay revealed 4 additional isolates that were resistant to OA (≥4 μg mL−1), making a total of 18 OA-resistant isolates obtained in this study. The results of DNA sequencing showed that missense mutations in both parC and gyrA but not in either gyrB or parE were identified in QR F. columnare isolates. Mutation in parC resulted in a change in His87-Tyr. For gyrA, 15 isolates of Thai origins exhibited change at residue 83 from Ser to either Phe, Tyr or Ala, whereas 3 Vietnamese isolates contained two mutation sites, Ser83-Ala and Asp87-Tyr.
Conclusion: This study is the first to reveal that QR phenotype of F. columnare isolates harbored missense mutations in both parC and gyrA but not in gyrB and parE of the QRDRs.
How to Cite: Jansen MD, Dong HT, Mohan CV (2018) Tilapia lake virus: a threat to the global tilapia industry? Review in Aquaculture. https://doi.org/10.1111/raq.12254 [open access].
Photomicrographs of haematoxylin and eosin‐stained sections of tissue from the liver, kidney and brain of normal fish (a, e, g) and TiLV‐infected fish (b–d, f, h). The infected liver tissue showed syncytial hepatocytes and foamy cytoplasm (b), intracytoplasmic inclusion bodies (c) and inflammation with pancreatic necrosis (d). Kidney tissue showed syncytial cells and severe infiltration of inflammatory lymphocytes (f). Brain tissue also showed syncytial cells and severe infiltration of inflammatory lymphocytes (h).
Tilapia lake virus (TiLV) is a recently described virus affecting wild and farmed tilapines. At present, it has been reported on three continents (Asia, Africa and South America) and the number of countries where the agent has been detected is likely to increase rapidly as a result of increased awareness, surveillance and availability of diagnostic methods. Any lack of openness regarding the TiLV status of a translocating live tilapia population destined for aquaculture may inadvertently contribute to the spread of the agent. Currently, there is no cure for viral diseases in aquaculture and while vaccines and selective breeding have proved successful in reducing the severity of some viral diseases, there are currently severe knowledge gaps relating to TiLV and no effective, affordable vaccines are yet available. This paper summarizes the published scientific information on TiLV and highlights important issues relating to its diagnosis, mitigation and control measures. While there have been no scientific studies on the socio‐economic impact of TiLV, it may pose a significant threat particularly to small‐scale fish farmers’ livelihoods and wild tilapine populations if left uncontrolled. To aid disease investigations, the authors propose case definitions for suspected and confirmed cases of TiLV infections.
- Detection of TiLV in clinically healthy adult and fingerling tilapia
- Histopathology resembling SHT was observed from TiLV-infected fish
- Low viral load in fish tissues was determined by RT-PCR
- Investigation of inapparent infection should be included in TiLV surveillance program
Tilapia farming has been affected by a newly discovered Orthomyxovirus-like, tilapia lake virus (TiLV), which has caused considerable economic loss to farmers. Currently, mortality-associated TiLV infections have been reported in tilapia farms in Israel, Ecuador, Colombia, Egypt, Thailand, Chinese Taipei, India and Malaysia. In this study, sets of samples collected from clinically healthy adult and fingerling tilapia with no signs of diseases or mortality were randomly diagnosed for TiLV. The tissue samples were examined by semi-nested RT-PCR, histopathology, and in situ hybridization (ISH). Unexpectedly, individual organs (liver, kidney, spleen, brain, and heart) of the tested adult fish (2/2) and liver of the fingerlings (9/19) exhibited positive results in the second step RT-PCR, indicating a low viral load of TiLV in the fish tissues. Sequencing analysis of 250-bp amplicons revealed 97.2% identity to the prototype strain from Israel. Histopathology was investigated in the adult fish specimens and pathological features resembling syncytial hepatitis were observed while ISH yielded no detectable signal. Unlike previous reports, this study revealed cases of inapparent or subclinical infections of TiLV in tilapia. Underlying factors and mechanisms between host and virus resulting in inapparent infection require further scientific investigation.
Keywords: Inapparent infection; TiLV; Tilapia lake virus; RT-PCR
An in vitro assessment of antimicrobial properties of aqueous and ethanol extracts from solo garlic (Allium sativum), garlic chive (Allium tuberosum) and betel leaves (Piper betle) on six bacterial pathogens in aquaculture, and a challenge of Nile tilapia, Oreochromis niloticus with Streptococcus agalactiae were performed. Generally, minimum inhibitory concentrations (MIC) ranged from 26.63 to 53.25 mg mL-1 for aqueous solo garlic (G) and 14.60 to 29.20 mg mL-1 for garlic chive extracts for all pathogens tested. Ethanol extract of betel leaves (P) exhibited the strongest antibacterial activity (0.15 – 0.60 mg mL- 1). P and G incorporated in feed at high and low doses as multiples of MIC [High; H (10X for PH and 3X for GH) and Low; L (3X for PL and 1X for GL)] were fed to tilapia followed by in vivo challenge against S. agalactiae (1 x 108 CFU mL-1). Ethanol extract of P. betle significantly improved survival (P < 0.05; PH=100%, PL =77%). White blood cells (WBC), lymphocytes and monocytes differed significantly (P < 0.05) among treatments and the highest WBC value (1.175 × 103) was for PH. Use of ethanol extract of Piper betle seems promising for sustainable disease management in aquaculture.
Keywords: herbal, antimicrobial, risk, haematology, survival
Source: Turkish Journal of Fisheries and Aquatic Sciences. DOI: 10.4194/1303-2712-v18_5_03