Masters Thesis
Bacteria under family Flavobacteriaceae (in this study were also referred to as
Flavobacteria) are important pathogens of fish, people, many other animals and
plants. In this study, Flavobacteria from Nile tilapia (Oreochromis niloticus) and
African catfish (Clarius gariepinus) were identified and characterized from the
selected farms in Uganda. Gill and skin swabs were obtained from a total of 119 fish
from 19 farms and were dissected aseptically to sample internal organs. The samples
were inoculated onto Sheih media and incubated at 25°C for 48 hours. The suspected
isolates were identified by colon characteristics, conventional biochemical tests and
API 20 NE kits. The isolates were grouped into eight based on colon characteristic
similarity. One isolate was selected per group for 16S rRNA gene sequencing and
identified using the EZbiocloud.net ID software. Phylogenetic analysis of selected
isolates was performed using the 16S rRNA gene sequences in BioEdit and MEGA
7.0.2 software. Basing on extrapolation of sequence analysis of the selected isolates,
out of the 86 isolates, Myroides marinus was the most predominant species taking up
4 of the 8 groups (60 isolates) in 13 farms. The rest of the groups comprised of;
Acinetobacter pitti, one group (6 isolates) in 6 farms, Chryseobacterium gambrini 2
groups (3 isolates) in 3 farms and one isolate was unidentified, in 3 farms. However, a
total of 16 isolates did not grow on sub culturing. Phylogenetic analysis indicated that
M. marinus isolates grouped with other M. marinus isolates from gene bank with
significant intra-species diversity which was also observed with C. gambrini isolates.
All the sampled farms had at least one isolate of a Flavobacterium from Tilapia
and/or Catfish. Pathogenicity studies should be conducted on the isolates to establish
their importance as fish pathogens and transmission dynamics so that an appropriate
control measure can be recommended.
TRAHESA NORHED