Phenotypic and molecular characterization of Riemerella anatipestifer isolates from ducks

Abstract

Riemerella anatipestifer cause one of the most economically important infectious diseases among the domesticated duck population. The present study was conducted to isolate R. anatipestifer and also to phenotypic and molecular characterization of the isolates. During the study period, 27 suspected field outbreaks were attended in five district of Assam. A total of 624 samples were collected and processed for isolation followed by phenotypic and molecular characterization. All confirmed isolates (n=95) were screened for two important virulence genes ompA and cam gene. Further, the confirmed field isolates were also subjected for antimicrobial resistant pattern against 28 most commonly used antimicrobial agents to determined suitable antimicrobial regime. Pathogenicity test was also conducted from isolates recovered from dead ducks in suitable host system. newlineOn bacteriological examination, 121 isolate (19.39%) could be recovered based on phenotypic characteristics (cultural, morphological and biochemical). Phenotypically, highest bacteria could be isolated from brain and heart tissue (28.57%) followed by spleen and liver (26.19%) and least from ocular swab (12.50%). All the isolates produced small, smooth, circular, mucoid, glistening and dew drop like colonies on blood agar under micro-aerophilic condition for 18-24hours. The colonies were found to be non haemolytic on blood agar except 4 isolate (11.12%), watery, discrete, translucent with characteristics odour of culture. Biochemically, all the isolates showed positive for catalase and oxidase test (100%), 97 isolates for gelatin liquefaction test (80.16%) whereas found negative for indole, methyl red, Vokes-Proskauer, H2S, ornithine decarboxylase etc. On sugar fermentation tests, 10 isolates revealed positive for trehalsoe and xylose (8.26%), 7 isolates for lactose (5.78%) test. Among the phenotypically identified suspected isolates only 95 isolates (78%.51) could be recovered through PCR assay targeting 16S rRNA, ERIC sequence and gyrB gene with equal positivity