MSc

ABSTRACT
Distribution of antibiotic resistance and public health significant virulence genes among Vibrionaceaee associated with Scylla olivacea (Herbst, 1896)
The study entitled “Distribution of antibiotic resistance and public health significant virulence genes among Vibrionaceae associated with Scylla olivacea (Herbst, 1896)” undertaken during 2019-20 at Marine biotechnology division, ICAR-Central Marine Fisheries Research Institute, Kochi. The study was performed to evaluate the incidence of vibrio related infections in both humans and aquatic animals continue to rise during the years to come driven by the climate change and ocean warming, demanding detailed studies about vibrios especially in terms of virulence and antibiotic resistance. Orange mud crab (Scylla olivacea Herbst, 1896) represents a prime component of aquaculture practices and coastal fisheries. Even though knowledge on abundance and composition of microbes in apparently healthy animals is essential in successful aquaculture practices, data availability on microbiology of these crabs are fewer. Therefore, investigations on Vibrionaceae (bacteria that are widely distributed in aquatic environments) in these animals will be valuable in both aquaculture and public health perspectives, which were targeted through the present study. Further, bacteria belonging to three public health significant Vibrio spp. (V. harveyi, V. parahaemolyticus and V. vulnificus) isolated from diseased fish were also included in the study. It was found that all tissues including haemolymph of S. olivacea carried a variable concentration of vibrios even in apparently healthy conditions with the greatest mean concentrations in gut (1.74 X 106 CFU/g), followed by gill (1.60 X 106 CFU/g). Haemolymph had the lowest mean concentration of vibrios (1.77 X 102 CFU/mL). There were a total of 23 morphologically different vibrio isolates which were found to be belonging to three distinct species in prevalence order of V. parahaemolyticus (56 per cent) > V.alginolyticus> V. diazotrophicus. Gut was having the maximum diversity. During phylogenetic analysis, there were two clades namely, Harveyi and Diazotrophicus clades, in which Harveyi clade was more dominant. Prevalence order of virulent genes was chiA (V. harveyi)> collagenase (V. parahaemolyticus)> toxR (V. parahaemolyticus) > toxR (V. alginolyticus) > nanH (V. cholerae). Antibiotic resistance pattern of all these isolates against a total of 21 antibiotics belonging to six classes were also studied and results showed that imipenem, nalidixic acid and chloramphenicol would be the most efficient antibiotics against vibrios. Among 18 antibiotic resistant genes screened, only four genes namely tetS, tetH, tetB and aphA3 were present in vibrio isolates of the present study with an overall prevalence of AR genes as 2.77 per cent. The study forms the initial report on occurrence of tetH and tetS among vibrios. In conclusion, the present study forms the first multi-tissue description on density and diversity of Vibrionaceae of a supreme aquaculture candidate crab species, fetching applications in disease management studies during their aquaculture practices. Furthemore, the generated ABST, profiles of virulence and AMR genes of vibrio isolates can pave the way for its additional applications in public health perspectives.