Microbiome analysis of gut bacterial communities of healthy and diseased Malaysian mahseer (Tor tambroides) using 16S rRNA metagenomics approach

Aims@#The gut microbiota is referred to as an ‘extra organ’ and is critical in assisting the host in terms of nutrition and immunity. Environmental stressors could alter the gut microbial community and cause gut inflammation. This study aimed to investigate and compare the gut microbiota community between healthy and diseased Tor tambroides.@*Methodology and results@#In this study, such gut microbial alterations were explored using NGS-based 16S rDNA targeted sequencing on the Malaysian mahseer (T. tambroides). Three healthy adult and three diseased adult Malaysian mahseers (showing signs of exophthalmia, coelomic distension and petechial haemorrhage) were obtained from LTT Aquaculture Sdn Bhd. Our results revealed significant differences in microbial diversity, composition and function between both populations of T. tambroides. Alpha diversity analysis depicts lower diversity of gut microbiota composition in diseased T. tambroides as compared to the healthy group. In particular, Enterobacteriaceae, Aeromonas, Bacteroides, Vibrio and Pseudomonas were found within gut microbiota of the diseased fishes. In addition, cellulosedegrading bacteria and protease-producing bacteria were identified from the gut of T. tambroides.@*Conclusion, significance and impact of study@#Thus, our findings emphasized on the association between the alteration in gut microbiota composition and infectious abdominal dropsy (IAD) in T. tambroides. This finding is important to provide basic information for further diagnosis, prevention and treatment of intestinal diseases in fish.

Biofilm forming ability of intermediate and saprophytic Leptospira on abiotic and biotic surfaces

Aims@#Leptospira spp. has the ability to develop biofilm communities and this attribute is an essential factor to leptospiral pathogenesis. This study aims to assess and quantify the biofilm forming ability of intermediate and saprophytic Leptospira strains.@*Methodology and results@#The biofilm assay was quantified on microtitre polystyrene plates (abiotic) and wood chips (Jelutong Paya hardwood) over a duration of 11 days. Phase contrast light microscope was used to assess the structure of the on the surface. The biofilm production on wood chips surface were approximately one times higher than on polystyrene plate surface indicating Leptospira strains were capable of forming higher quantity of biofilm on biotic surface compared to abiotic surface by both intermediate and saprophytic Leptospira. A significant difference (p<0.05) exists in biofilms produced by Leptospira on wood surface which formed more biofilm than on polystyrene surface. The strongest biofilm producer is intermediate strain G14 with OD600 of 2.283±0.180 and OD600 of 2.333±0.037, on polystyrene and wood surface, respectively. Visualisation of biofilm by phase-contrast microscopy of two representative strains correlated with the OD values and the colour intensity of stained microtitre plates and wood surfaces. The biofilm formed comprises of a three-step process are adherence (1 th to 24 th h), maturation (6t h to 7 th day) and detachment (9 th to 11 th day) of biofilms.@*Conclusion, significance and impact of study@#The contact time of intermediate pathogenic strains was faster compared to saprophytic strain, indicating the biofilm forming ability is related to the level of pathogenicity of Leptospira strains.

Genomic Diversity of Cholera Outbreak Strains in East Malaysia

Thirty one Vibrio cholera isolates recovered from cholera outbreak in Bintulu, Sarawak (Malaysia) were detected with the presence of ctx gene by using specific PCR. These isolates were further characterized and differentiated by using the Enterobacterial Repetitive Intergenic Consensus PCR (ERIC-PCR) and BOX-PCR to determine their genomic fingerprints. The specific PCR result confirmed the identities of 27 isolates out of 31 as pathogenic V. cholerae. The ERIC-PCR generated several genetic profiles consisting of 4-6 bands with sizes in the range of 100 to 600 bp, while the BOX-PCR produced profiles numbering 2-7 bands in the sizes between 200 to 1000 bp. Based on the dendrogram generated from the DNA fingerprinting profiles (ERIC-PCR and BOX-PCR), all of the isolates can be divided into 2 main clusters that is further divided into 2 sub-clusters. The low genetic diversity of the isolates indicated the outbreak of V. cholerae in the study area was due to the contamination from a single or few sources of V. cholerae.