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All Journal HAYATI Journal of Biosciences Asian Journal of Agriculture
Thi, Quach Van Cao
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Agriculture, Biological Sciences & Forestry Earth & Planetary Sciences

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Identification and Antibiotic Resistance Edwardsiella tarda from Clown Knifefish (Chitala chitala) in the Mekong Delta, Vietnam Dung, Tu Thanh; Thi, Quach Van Cao; Trung, Nguyen Bao
HAYATI Journal of Biosciences Vol. 31 No. 4 (2024): July 2024
Publisher : Bogor Agricultural University, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.4308/hjb.31.4.641-651

Abstract

This investigation is intended to isolate, identify, and assess the pathogenicity of Edwardsiella tarda, which originated from diseased clown knifefish. A total of 43 isolates were obtained from infected fish samples in Hau Giang and Dong Thap provinces of the Mekong Delta, Vietnam. Two isolates of DT37 and HG41 were identified as E. tarda by morphological, biochemical, and 16S rRNA gene sequencing. Experimental challenge studies revealed that isolate DT37 leads to 83.33% at a 108 CFU/ml concentration after 60 hours. Meanwhile, in isolate HG41, mortality reached 100% within 48 hours post-injection at the highest concentration of 108 CFU/ml. The challenged clown knifefish exhibited gross signs of abnormal swimming, skin ulcerations, and petechial hemorrhages in the body. Internally, ascites with hemoperitoneum, light-colored nodules on the liver, hemorrhagic kidneys, and splenomegaly were also recorded. The LD50 of two isolates, DT37 and HG41, was 4.89 × 105 and 4.07 × 105 CFU/ml, respectively. The antibiogram result showed that most of the isolates were highly susceptible to ampicillin (65%), enrofloxacin (85%), florfenicol (100%), flumequine (90%), cefotaxime (80%), and trimethoprim and sulfamethoxazole (70%). However, the bacterial isolates were highly resistant to doxycycline (75%) and streptomycin (100%).
Streptococcus agalactiae Associated with "Dark Body" Disease on Snakeskin Gourami Farmed in the Mekong Delta, Vietnam Dung, Tu Thanh; Thi, Quach Van Cao; Trung, Nguyen Bao
HAYATI Journal of Biosciences Vol. 31 No. 3 (2024): May 2024
Publisher : Bogor Agricultural University, Indonesia

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.4308/hjb.31.3.486-497

Abstract

Streptococcosis, due to Streptococcus agalactiae, has become a serious challenge for aquaculture around the world. Therefore, the main purpose of this work was to confirm the etiological agent that caused "dark body" disease in snakeskin gourami (Trichogaster pectoralis) cultured in the Mekong Delta, Vietnam. Infected fish displayed clinical signs, including anorexia, lethargic swimming on the water surface, corneal opacity, and hemorrhage in the base of the fin. Remarkably, abnormal black coloration on the body and serious hemorrhage at the base of the pectoral fin, and on the body were found in infected fish. In total, 75 bacterial strains were isolated from different diseased fish farms. Based on morphological and physiological characteristics, the API 20 Strep test, and 16S rRNA sequence analysis, the result illustrated that the bacterial isolates were identified as S. agalactiae. Additionally, antibiotic sensitivity testing revealed that all the S. agalactiae isolates were sensitive to amoxicillin, rifampicin, clarithromycin, erythromycin, doxycycline, cephalexin, novobiocin, and sulfamethoxazole-trimethoprim. Interestingly, S. agalactiae strains were only resistant to gentamycin in this study. Two strains, SRT41 and SRT43, carried out an experimental challenge with concentrations from 104 to 107 CFU/ml in healthy snakeskin gourami, and the LD50 values of the isolates, SRĐT41 and SRĐT43, were determined to be 2.15 × 105 and 3.59 × 103 CFU/ml, respectively, after 7 days. To our knowledge, this is the first report of S. agalactiae derived from intensively cultured snakeskin gourami in the Mekong Delta, Vietnam.
Antifungal potential of Enydra fluctuans extract for postharvest control of Colletotrichum siamense in dragon fruit TRUC, NGUYEN TRUNG; THI, QUACH VAN CAO; NHUNG, DUONG THI CAM
Asian Journal of Agriculture Vol. 10 No. 1 (2026)
Publisher : Smujo International

Show Abstract | Download Original | Original Source | Check in Google Scholar | DOI: 10.13057/asianjagric/g100100

Abstract

Abstract. Truc NT, Thi QVC, Nhung DTC. 2026. Antifungal potential of Enydra fluctuans extract for postharvest control of Colletotrichum siamense in dragon fruit. Asian J Agric 10 (1): g100127. https://doi.org/10.13057/asianjagric/g100127. Pitaya, commonly known as red-fleshed dragon fruit, is rich in bioactive and nutritional compounds; however, its postharvest shelf life is limited due to high susceptibility to fungal diseases, particularly anthracnose caused by Colletotrichum spp. These infections significantly reduce fruit quality, shorten storage duration, and decrease economic value. This study investigated the antifungal efficacy of Whole Enydra fluctuans Phenolic Extract (WEPE) against postharvest pathogens of dragon fruit under in vitro and in vivo conditions. Fifteen fungal isolates were recovered from infected fruits, among which strain TL12 was identified as Colletotrichum siamense based on morphological characteristics and ITS rDNA sequencing. Pathogenicity tests confirmed Koch’s postulates, producing disease symptoms comparable to those observed in naturally infected fruits. To the best of our knowledge, this is the first report of C. siamense associated with postharvest anthracnose of dragon fruit in the studied region. WEPE obtained using ultrasound-assisted extraction with 45% ethanol exhibited the highest total phenolic content (18.26±1.49 mg GAE/g). In vitro assays demonstrated strong antifungal activity, with minimum inhibitory concentrations of 700 μg/mL for complete mycelial growth inhibition and 5000 μg/mL for spore germination inhibition. In vivo application of WEPE significantly suppressed anthracnose development on dragon fruit in a concentration-dependent manner. After 7 days of incubation, disease severity was reduced by approximately 30.4% and 55% at 700 and 5000 μg/mL, respectively, compared to the control. The results indicate that WEPE possesses strong antifungal potential against C. siamense and may be considered a promising natural agent for postharvest disease management in dragon fruit. However, these findings are based on short-term storage experiments under controlled laboratory conditions. Further research involving formulation optimization, extended storage evaluation, and field-scale validation is necessary before practical application in commercial postharvest systems.
Co-Authors Dung, Tu Thanh NHUNG, DUONG THI CAM TRUC, NGUYEN TRUNG Trung, Nguyen Bao