Nguyen Phuong Thuy, Nguyen Ngoc Trai, Bui Dang Khoa, Nguyen Hoang Xuan Thao, Vuong Tuan Phong, Quach Van Cao Thi. Plant Breed. Biotech. 2023;11:117-29. https://doi.org/10.9787/PBB.2023.11.2.117

Quach VCT, Tran QD, Ha NH, Nguyen BT, Tu TD, Nguyen PT. 2023. Antibacterial activity of lactic acid bacteria from various freshwater fish species against pathogenic bacteria in caged red tilapia (Oreochromis sp.). Biodiversitas 24: 3373-3383. Antibiotic-resistant bacteria are a big challenge for many aquaculture countries around the world. The search for new solutions, such as probiotics to replace antibiotics in aquaculture, attracts the interest of many scientists. The investigation was accomplished by isolating Lactic Acid Bacteria (LAB) inhibiting Streptococcus agalactiae and Aeromonas hydrophila, which cause swollen eyes and hemorrhagic skin disease in caged red tilapia (Oreochromis sp.) in Vinh Long province. The findings isolated 37 isolates of LAB from the intestines of catfish, red tilapia, and tilapia. Using the diffusion well method, the results showed that 13/37 (35.14%) and 18/37 (48.65%) isolates were inhibitory against S. agalactiae and A. hydrophila, respectively. The research found that eight isolates were inhibitory to two species of S. agalactiae and A. hydrophila, especially isolate CT6.2, which has the strongest inhibition (10.5 mm inhibition zone diameter). Our finding revealed that the isolates CT6.2 and RP6 demonstrate the highest antagonistic activity against S. agalactiae and A. hydrophila at a density of 108 CFU/mL after incubation at 35°C, pH = 5-6 for 48-60 h. Using PCR techniques and 16S rRNA gene sequencing combined with morphological and biochemical characteristics, the LAB isolates in the findings belong to the genera Lactobacillus and Pediococcus, being 99.35% and 99.02% similar to Lactobacillus plantarum and Pediococcus pentosaceus, respectively. This is the first report on the antimicrobial activity of LAB against S. agalactiae and A. hydrophila in caged red tilapia in the Mekong Delta.

Antimicrobial resistance from bacterial pathogens is becoming a health concern in many countries. The purpose of this investigation was to assess antimicrobial resistance and find out the prevalence of class 1 integrons from A. hydrophila that led to hemorrhagic disease in intensively farmed Tra catfish in the Mekong Delta, Vietnam. The research showed that a total of 74 isolates were isolated and identified as A. hydrophila by the API 20E kit and using the amplification products of the aerolysin gene for confirmation. The susceptibility of all isolates was tested against fifteen antimicrobial agents using the disk diffusion method. Our study indicated that most strains were resistant to the following antibiotics: trimethoprimsulfamethoxazole, ampicillin, cefalexin, tetracycline, amoxicillin, chloramphenicol, florfenicol, neomycin, and gentamycin. In addition, the investigation also indicated that most A. hydrophila isolates displayed multiple antibiotic resistance phenotypes. The MAR (multiple antibiotic resistance) index was high, ranging from 0.40 to 0.66 for A. hydrophila isolates, which indicated that these isolates were exposed to high risk sources of contamination where antibiotics were commonly used. Among all isolates, 12.16% (9/74 isolates) of class 1 integrons were determined by polymerase chain reaction

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%).

Thi QVC, Minh NLK, Thuy NP, Tat TQ, Tran T. 2024. Characterization of endophytic bacteria isolated from wild rice plants in the Mekong Delta, Vietnam. Biodiversitas 25: 2576-2585. Endophytic bacteria bring many benefits to plants, such as stimulating plant growth and inhibiting many microbial pathogens that cause plant diseases. Hence, this investigation aimed to evaluate the association of endophytic bacteria with wild rice (Oryza rufipogon) that can fix nitrogen, solubilize phosphorus and produce indole-3-acetic acid (IAA). Twelve-five bacterial strains were recovered from wild rice stems and roots collected from Vinh Long and Tien Giang provinces of the Mekong Delta. Among these strains, six had phosphorus solubilizing and seven had nitrogen-fixing activity. Strain BR3.5 fixed the highest nitrogen, i.e. ammonia (NH4+) content of 0.109 ± 0.002 mg/L after eight-day incubation. However, the highest phosphorus solubilization was recorded in two isolates, RR3.7 and RR1.1, with clear zone diameters of 0.800 ± 0.020 mm and 0.800 ± 0.030 mm, respectively. In addition, bacterial strains could synthesize IAA, and BR2.5 produced the highest, i.e., 0.067 ± 0.002 ?g/mL, IAA after eight-day incubation. Notably, strain BR3.5 exhibited multiple activities like nitrogen fixation (0.109 ± 0.002 mg/L), phosphorus solubilization (1.02 ± 0.002 mm), and IAA synthesis (0.056 ± 0.00 ?g/mL). Strain BR3.5 was identified as Pantoea sp. based on 16S rRNA gene sequencing (92.69% similarity) together with morpho-physiological and biochemical characteristics. The findings indicate that strain BR3.5 may be used for the production of biofertilizers for rice farming.

Vibrio parahaemolyticus is well known as the primary causative agent of acute hepatopancreatic necrosis (AHPND) in white leg shrimp (Litopenaeus vannamei) aquac