Phenotypic characterization and presumptive identification of bacterial isolates from moribund Nile tilapia (Oreochromis niloticus L.)

Abstract

The general objective of this study was to isolate, characterize and presumptively identify bacterial isolates from moribund Nile tilapia (Oreochromis niloticus L.). The rigid sorting of the bacterial colonies based on cultural characteristics has resulted to three different bacteria. Colony A and colony B shared the same cultural characteristics – round with raised margin, small in size, and with entire margin, smooth texture and convex elevation. Colony C was entirely different in shape, margin, texture and elevation. The three bacterial colonies failed to grow in McConkey Agar but luxuriously grow in Staphylococcus Selective Agar, therefore, colony A and colony B were presumptively identified under the genus Staphylococcus. Colony A and colony B were Gram-positive, spherical in shape, positive to catalase test, and negative to several tests such as citric acid utilization, urea hydrolysis and phenylalanine deamination.