Silver nanoparticles (AgNPs) were biosynthesized using Fortunella Japonica extract as an reducing agent through a rapidly and ecofriendly assisted ultrasound method. Effect of ultrasound assistant on synthesis duration, properties and antibacterial activity of AgNPs against Escherichia coli, Bacillus subtilis and Bacillus cereus were reported. The suitable duration for AgNPs assisted ultrasound biosynthesis was 90 minutes that is 60 minutes shorter than stirring-assisted method. The obtained AgNPs with a face centred cubic structure were nearly spherical in shape and uniform in size distribution with the average nanosize of 11.6 nm, being smaller than the size of AgNPs prepared by stirring-assisted method. AgNPs sample exhibited effective antibacterial activity against all three bacteria with average diameter of inhibition zones of over 15 mm and minimum inhibitory concentration of 4.13 µg/mL. The results showed that the ultrasound assistant has positive effects such as shortening synthesis duration, reducing average particle size and increasing antibacterial activity of AgNPs.

In this study, we isolated 28 strains of Bacillus spp. from water samples, catfish pond mud samples and earthworm manure (Perionyx excavates). By the cross-streak agar methods, 22 Bacillus strains showed the inhibition ability to Edwardsiella ictaluri, which caused Bacillary Necrosis Pangasius (BNP) in catfish (Pangasianodon hypophthalmus). Both Bacillus sp. Q16 and Q111 strains showed the highest inhibition to E. ictaluri by the double-layer agar methods. Finally, two Bacillus strains (Q16, Q111) were selected as a source of potential probiotic because of the ability of extracellular enzyme secretion (protease, amylase, cellulose) strong growth at 0,1-1% salt concentrations, survival within the pH range 6-8, resistance to low pH and low bile salts, inability to produce haemolysin enzyme, sensitivity to eight antibiotics in the three impacting groups (inhibition of wall synthesis, inhibition mechanism of protein synthesis, inhibition of nucleic acid synthesis). Two Bacillus strains (Q16, Q111) were identified that they belong to Bacillus subtilis by biochemical method and 16S rRNA gene sequencing method. This study indicated that two Bacillus strains (Q16, Q111) isolated from catfish pond can be applied as high potential probiotics that used to farm catfish.

28 leaves and living-tissue samples of rubber tree (Hevea brasiliensis) were collected from Ho Chi Minh City, Binh Phuoc province and Binh Duong province (Viet Nam). We isolated and screened endophytes that have potential application as agents for biocontrol of Corticium salmonicolor, the agent of Pink Disease in rubber trees. As a result, 21 strains of endophytic bacteria and 14 strains of endophytic fungi were isolated. Antagonistic activity of the endophytes towards C. salmonicolor was checked by using a dual culture. Testing results showed that: T9, T15 and T16 strains have inhibited C. salmonicolor. T9 and T16 strains showed result that 100% of inhibiting C. salmonicolor at the concentration of 1:1. In the test of ability to kill C. salmonicolor, T9 and T16 strains showed that they could kill C. salmonicolor after 3 sprays of bacterial filtrate. T9 and T6 strains, which were identified by biochemical methods, have similar characteristics to Bacillus thuringiensis.

Bệnh hoại tử gan tụy ở tôm được phát hiện đầu tiên ở Trung Quốc năm 2009 và gây hại cho nghề nuôi tôm ở nhiều nước kể cả Việt Nam. Trong nghiên cứu này, chúng tôi sàng lọc khả năng kháng Vibrio parahaemolyticus gây bệnh hoại tử gan tụy của một số chủng Bacillus. Chủng V. parahaemolyticus NT7 sử dụng trong nghiên cứu này được phân lập từ mẫu tôm thẻ chân trắng bệnh hoại tử gan tụy tại Ninh Thuận và đã được định danh bằng phương pháp sinh hóa. Bằng phương pháp vạch vuông góc và giếng khuếch tán, chúng tôi sàng lọc được chủng Bacillus polyfermenticus F27 đối kháng V. parahaemolyticus NT7 với đường kính lớn nhất là 18,50 mm. B. polyfermenticus F27 có khả năng ức chế V. parahaemolyticus NT7 khi tiến hành đồng nuôi cấy, không gây tiêu huyết và an toàn đối với tôm thẻ giống với tỷ lệ sống 100% của nghiệm thức thử nghiệm. Kết quả khảo sát LD50 khi gây nhiễm V. parahaemolyticus NT7 lên tôm thẻ giống là 1,12. 105 CFU/ml. Tiến hành thử nghiệm đánh giá khả năng bảo vệ vật chủ của chủng B. polyfermenticus F27, chúng tôi nhận thấy chủng có khả năng bảo vệ tôm thẻ giống từ chủng V. parahaemolyticus NT7 gây bệnh. Những kết quả trên cho thấy rằng chủng Bacillus polyfermenticus F27 có tiềm năng để sản xuất chế phẩm sinh học kiểm soát và phòng bệnh EMS/AHPNS trên tôm.

The objective of this study is to isolate endophytic bacteria from Azadirachta indica (neem). We isolated 7 strains of endogenous bacteria from the neem tree. By investing the anti-fungal and antibacterial activities of endophytic bacteria in A. indica by well diffusion agar method, we noticed there was KT2 strain which resisted to Salmonella typhi and Staphylococcus aureus (10.67 ± 0.33 mm and 9.67 ± 0.33 mm), KT3 strain showed the inhibitory activity to three human pathogenic fungal (Candida albicans, Trichophyton mentagrophytes, Trichophyton rubrum), two strains (KT1, KT2) which resisted to C. albicans and T. rubrum. According to Cowan and Steel's manual, the result of biochemical identification showed that the KT2 strain was the Bacillus subtilis species.