Investigation of a bacterial pathogen isolated from farmed Ompok pabda

Abstract

Studies were conducted to isolate and identify a pathogen collected from the hemorrhagic ulcer of
farmed Ompok pabda and to determine the pathogenic potentiality as well as antibiotic susceptibility of the
recovered isolate. Infected fish were collected from a local fish farm located at Ishwarganj under
Mymensingh district, Bangladesh. The bacterial isolate was identified by using Hi Assorted™ Biochemical
Test kit and further investigated to determine the antibiotic susceptibilities. To determine the virulence, a
challenge model was performed using the experimental bacterium, Ar-9 by intramuscular injection of O.
pabda. A total of 50 healthy experimental fish (2.3±0.44 g) were used in another challenge test by using
single intramuscular injection with a pre-fixed dose (107 CFU/ fish) to find out the therapeutic effects of
various available antibiotics. The results demonstrated that the collected isolate was Gram-negative rod
shaped bacterium exhibiting non-wrinkled, smooth and slightly yellowish colony on TSA from 8 to 42?C.
Biochemical identification revealed that causative bacterium (Ar-9) was Aeromonas sp. that showed variable
susceptibilities against different antibiotics but marked resistance to ampicillin. Ar-9 was found virulent (LD50
= 2.2× 106.0) to O. pabda. Moreover, experiment on the therapeutic effects against the infectivity of Ar-9
revealed that CFCIN have successfully recovered 100% of challenged fish followed by O. T. C. power,
Tylovet and ATIVET. Thus, the present study revealed a virulent and ampicillin resistant pathogenic
bacterium which may be harmful in pabda culture in Bangladesh.