Pathogenecity and antimicrobial susceptibility of bacteria isolated from kidney, liver, and brain of Nile tilapia (oreochromis niloticus) stocked in intensive cage farming systems in Taal Lake, Batangas

Date of Publication


Degree Name

Master of Science in Biology


College of Science



Thesis Adviser

Eguia, Maria Rowena R. Romana

Defense Panel Chair

Cabrera, Esperanza C

Defense Panel Member

Lagman, Ma. Carmen A.
Somga, Joselito R.
Alea, Glenn V., Dean


Tilapia disease outbreak and fish kills have been ever pressing problems of tilapia farmers in Taal lake, but the bacterial etiology of the disease is still unknown. In the Philippines, limited studies have been conducted on the pathogenecity and antimicrobial susceptibility of bacterial isolates in aquaculture. Hence this study was undertaken to identify the bacteria of diseased tilapia in Taal Lake and determine their antimicrobial susceptibility and pathogenicity. A total of 181 bacteria were isolated from diseased Nile tilapia in Taal Lake. The commonly isolated bacteria were aeromonas hydrophila/caviae (41.99%), streptococcus agalactiae (19.89%), plesiomonas shigelloides (5.52%), aeromonas sobria (3.78%) and vibro cholerae (2.76%). Aermonas spp. and plesiomonas shigelloides isolates were chosen and tested against 11 antimicrobials. The antimicrobial susceptibility patterns of the isolates revealed resistance to at least one antimicrobial. All isolates showed susceptibility to ceftriaxone and chloramphenicol, while 50 (80%) of the isolates were found resistant to cefoxitin. A multyiple antibiotic resistance (MAR) index value of <0.2 was found on 97.14% of the bacterial isolates, which indicated that Taal Lake has low risk of antibiotic contamination. Two bacterial isolates, streptococcus agalactiae and aeromonas hydrophila, were tested for their pathogenicity in juvenile Nile tilapia. Pathogenicity test results proved that S. agalactiae and A. hydrophila were pathogenic to tilapia, and suggested that the gross clinical signs and internal abnormalities observed in the diseased Nile tilapia in Taal Lake were caused by S. agalactiae and/or A. hydrophila infection. At 96 h post infection, the median lethal dose (LD50) of S. agalactiae and A. hydrophila in juvenile Nile tilapia were 2.27 x 102 CFU/fish and 1.34 x 102 CFU/fish, respectively. Results of this study highlights the importance of antimicrobial susceptibility testing and pathogenicity test in the surveillance of pathogenic and antibiotic resistant bact

Abstract Format




Accession Number


Shelf Location

Archives, The Learning Commons, 12F Henry Sy Sr. Hall

Physical Description

1 computer disc ; 4 3/4 in.


Tilapia -- Philippines

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