Molecular characterization and antibiogram of Riemerella anatipestifer in ducklings in Upper Egypt

Riemerella anatipestifer infection represents a great threat to the duck industry worldwide and it is considered the major cause of death in the backyard rearing system of ducks in Egypt. The disease is characterized by diarrhea, respiratory signs and loss of weight. The present study was conducted during the period between July 2019 and January 2021 to examine the prevalence rate, the antibiogram patterns of the different antibiotics and the pathogenicity of R. anatipestifer in Qena province. One-hundred samples were collected from diseased and freshly dead backyard ducklings. A tentative characterization of R. anatipestifer was done depending on the phenotypic characteristics (colony morphology and biochemical reactions). The molecular identification using PCR assay targeting the 16S rRNA gene resulted in a 6% prevalence rate of R. anatipestifer. Results of MIC for the 6 R. anatipestifer isolates against 7 antibacterial agents resulting in 5 isolates (83.3%) being resistant to ampicillin; 4 isolates (66.7%) were resistant to doxycycline, sulphamethoxazole and Cephradine. All isolates (100%) were sensitive to ciprofloxacin, 5 isolates (83.3%) were sensitive to amoxicillin and 4 isolates (66.7%) were sensitive to gentamycin. The experimental pathogenicity of the 6 isolates of R. anatipestifer on 14-day-old ducklings showed facial swellings, respiratory signs and greenish diarrhea. All ducklings in the 6 groups showed a significant decrease in body weight when compared with the negative control group. The study concluded that the R. anatipestifer was prevalent in Qena province with a variable resistance and susceptibility pattern for the different antimicrobial agents.