UNDERSTANDING THE EFFECTS OF SALINITY AND VIBRIO HARVEYI ON THE GUT MICROBIOTA PROFILES OF LITOPENAEUS VANNAMEI

 Zulaikha Mat Deris a, †, Shumpei Iehata b, †, Han Ming Gan c, Mhd Ikhwanuddin d, Musa Najiah b, Md Asaduzzaman e, Wang Min f, g, Liang Yantao f, g, Muhd Danish-Daniel a, Yeong Yik Sung a.g, Wong Li Lian a,g, *

a Institute of Marine Biotechnology, Universiti Malaysia Terengganu, 21030 Kuala Nerus,

Terengganu, Malaysia

b Faculty of Fisheries and Food Science, Universiti Malaysia Terengganu, Kuala Nerus,

Terengganu, Malaysia

c GeneSeq SDN BHD, 48300 Bandar Bukit Beruntung, Selangor Darul Ehsan, Malaysia

d Institute of Tropical Aquaculture and Fisheries Research, Universiti Malaysia Terengganu, 21030 Kuala Nerus, Terengganu, Malaysia

e Department of Marine Bioresource Science, Faculty of Fisheries, Chattogram Veterinary and Animal Sciences University, Khulshi 4225, Chattogram, Bangladesh

f College of Marine Life Sciences, Frontiers Science Center for Deep Ocean Multispheres and Earth   System,    Institute    of    Evolution    and    Marine    Biodiversity,    Ocean University of China, Qingdao, China

g UMT-OUC Joint Academic Center for Marine Studies, Universiti Malaysia Terengganu, 21030, Kuala Nerus, Malaysia

 *Corresponding author: lilian@umt.edu.my

† These authors contributed equally to this work

Increasing shreds of evidence have revealed a positive correlation between gut microbiota and shrimp health, in which a healthy shrimp gut is consisted of a complex and stable microbial community. Given that both abiotic and biotic factors constantly regulate shrimp gut microbiota, the climatic changes affecting the levels of these factors could cause disease outbreaks. The goal of this study was to explore the effects of salinity levels and pathogenic Vibrio harveyi infection on the diversity, structure, composition, interspecies interaction, and functional pathways of Penaeus vannamei gut microbiota. Juvenile shrimp were cultured at 5 ppt, 20 ppt, and 30 ppt (control condition) for two months prior to Vibrio harveyi infection. After the 24-hour challenge test, genomic DNA was isolated from the shrimp gut, and subjected to the 16S rRNA metagenomic sequencing analysis. We observed that gut microbiota diversity of shrimp cultured at 5 ppt and 30 ppt were lower than 20 ppt after exposure to V. harveyi infection, suggesting that shrimp cultured at the two former salinity levels were more susceptible to disease infection. Network analysis also showed that shrimp cultured at 20 ppt exhibit a more stable bacterial network with complex interspecies interaction, even after induced by V. harveyi. Moreover, the presence of a high number of beneficial bacteria such as Pseudoruegeria, Rhodovulum, Ruegeria, Shimia and Lactobacillus in shrimp cultured at 20 ppt might have played a role in inhibiting the growth of V. harveyi and other potentially pathogenic bacteria. Bacterial functional pathway prediction has also detected a significantly higher biofilm formation process in the gut microbiota of shrimp cultured at 20 ppt, following V. harveyi infection. Collectively, our results suggested that 20 ppt is an optimal salinity that suppresses the growth of V. harveyi and potentially pathogenic bacteria in the shrimp gut, which could possibly minimize the risk of disease infection in shrimp for healthy shrimp production.

Keywords: Pacific white shrimp; climate change; 16S rRNA metagenomic sequencing; shrimp immunity; abiotic factors

ANTIMICROBIAL ACTIVITY OF GARLIC JUICE EXTRACT AGAINST FRESHWATER FISH BACTERIA ISOLATED FROM CAGE CULTURED PANGASIUS HYPOPHTHALMUS AND OREOCHROMIS SPP.

1. Syafiq-Syauqi¹, M Nur-Nazifah¹, Shaharah, M., I.², Firdaus Nawi, M.²

1Department of Marine Science, Kulliyyah of Science, International Islamic University Malaysia (IIUM), Bandar Indera Mahkota, Jalan Sultan Ahmad Shah, 25200 Kuantan, Pahang, Malaysia

2Fisheries Research Institute (FRI), Department of Fisheries, Tanjung Demong, 22200 Kampung Besut, Terengganu, Malaysia

*Corresponding author: nurnazifah@iium.edu.my

Garlic (Allium sativum) has several bioactive compounds that provides various biological properties such as growth promotion and antimicrobial properties which can increase fish resistance to aquaculture diseases. Pangasius hypophthalmus is a predominant finfish which originated from Mekong Delta region,Vietnam and has been cultured widely in Malaysia. The common pathogenic bacteria which can infect this species are E. ictaluri, A. hydrophila, and P. shigelloides. Meanwhile, Oreochromis spp. (tilapia) are mainly freshwater fish that inhabit shallow streams, rivers, or lakes and it has been widely cultured in many tropical and subtropical regions of the world. The common pathogenic bacteria infected this species are S. agalactiae and S. iniae. The objective of this study is to investigate the in vitro antibacterial activity of garlic juice extract against freshwater fish bacteria. First, garlic juice extract were prepared by using juice extractor. Next, 5 different bacteria which were E. ictaluri (Wild & ATCC), A. hydrophila, P. shigelloides, S. iniae and S. agalactiae were cultured onto solid media. Then, the antimicrobial sensitivity test was conducted where 30𝜇L of 5 different concentrations of garlic juice extract (20%, 40%, 60%, 80%, 100%), OTC and ethanol were placed onto disc and the inhibition zone were observed after bacterial incubation. The result of this study showed that garlic juice extract has a very good antibacterial activity for E. ictaluri, A. hydrophila, and P. shigelloides. Meanwhile, garlic juice extract showed a very low antibacterial activity for S. iniae and S. agalactiae. In conclusion, garlic juice extract can be used against E. ictaluri, A. hydrophila, P. shigelloides based on this in vitro study.

Keywords: Allium sativum, Pangasius hypophthalmus, Oreochromis spp., E. ictaluri, A. hydrophila, P. shigelloides, S. iniae, S. agalactiae, Antimicrobial Sensitivity Test

ISOLATION AND CHARACTERIZATION OF BACTERIAL INFECTION HEMORRHAGIC DISEASE ON ASIAN SWAMP EEL (MONOPTERUS ALBUS ZUIEW, 1793) IN THE MEKONG DELTA, VIETNAM

Thanh Si Nguyen¹, Trung Bao Nguyen², Khoi Minh Le², Dung Thanh Tu^2*

1 Advanced Program in Aquaculture Course 44, College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam

2 College of Aquaculture and Fisheries, Can Tho University, Can Tho City, Viet Nam

*Corresponding author: ttdung@ctu.edu.vn

Motile Aeromonas species are known as one of the major pathogens causing hemorrhagic diseases in numerous aquatic animals all over the world. In Asian swamp eel (Monopterus albus) farming in the Mekong Delta of Vietnam, the hemorrhagic disease is a severe disease that causes high mortality and significant economic losses. This study aimed to determine the causative agent of hemorrhagic disease in Asian swamp eels during the nursing stage. Several clinical signs were observed, such as red swollen vents, abdomen hemorrhage, head edema, and internal organ hemorrhage. All possible pathogens from the diseased eel were considered and isolated on Tryptone Soya Agar and Blood agar from the liver, and kidney. A total of 52 bacterial strains were isolated from diseased eel farms in Hau Giang and Can Tho, Vietnam. After 24 hours of incubation at 28 °C, the bacterial morphology analysis revealed that the colonies were Gram-negative, short rod-shaped, cream-colored with colonies measuring 0.1- 0.3 mm. Furthermore, a conventional identification system examination indicated the presence of two types of motile Aeromonas spp. The partial sequencing of the 16S rRNA gene confirmed that these two groups were Aeromonas hydrophila and Aeromonas veronii. A 50% lethal dose (LD₅₀) trial on healthy Asian swamp eels (4±0.9 g) using A. hydrophila CT07 and A. veronii HG43 showed that the LD₅₀ values were 1.51×10⁶ and 1.74×10⁶ CFU/mL after  14 days of injection, respectively. The results of the experimental injection challenge study fulfilled Koch’s postulates, and the clinical signs of challenged Asian swamp eels were similar to those observed from infected eels on farms. In addition, the antimicrobial sensitivity tests were performed on ten isolates using eleven different antibiotics in this study.

Keywords: Aeromonas hydrophila, Aeromonas veronii, Asian swamp eel, hemorrhagic disease.