Phenotypic and Genotypic Characterization of Some Pseudomonas sp.Associated with Burkholderia cepacia Isolated from Various Infected Fishes

Abstract

This study aims to characterize Pseudomonas species that had been isolated from various naturally diseased fresh and marine water fishes, Nile tilapia, catfish, gilt-head bream, and Sea bass using phenotypic method, morphology and biochemistry characters using API 20NE, and genotypic method (16S rRNA gene sequencing) with some of the histopathological characteristics. Six of seven presumptive Pseudomonas sp. were successfully identified by API 20NE method to level species; they were identified as 2 P. fluorescens, one P. putida, one Pseudomonas sp and 3 Burkholderia cepacia while genotypically with 16S rRNA gene sequencing that proved successful for all the four pseudomonas isolates (three as P. fluorescens and one P. putida). The results of phylogenetic analysis placed the isolates in the genus Pseudomonas based on 99% homology. Challenged test revealed that, P. fluorescens and P. putida are to be classified as pathogenic for O. niloticus and they also exhibited clinical signs and mortality rates up to 70% and showed histopathological changes of both liver and kidney which lead to death. The antibiogram study showed that no significant differences between P. fluorescens and P. putida which had intrinsically high sensitivity to nucleic acid synthesis inhibitors such as ciprofloxacin, norfloxacin, gentamycin, gatifloxacin, lomefloxacin and kanamycin. This study concluded that good overall agreement between phenotypic and genotypic identification procedures was found for the isolates with some minor differences in biochemical and physiological characteristics were observed between P. fluorescens strains, while the genotypic differences were significant observed between P. fluorescens and P. putida isolated from various fishes.