Virulence attitude estimation of Pasteurella multocida isolates in embryonated chicken eggs.

Abstract

A total of 220 birds of age ranging from 3 to 14&#xa0;weeks old were collected from several backyards and different farms in Sharkia Governorate, Egypt, and surveyed for the presence of fowl cholera. Twenty Pasteurella multocida from chickens (15/145, 10%) and ducks (5/75, 6%) were bacteriologically isolated,&#xa0;and it was shown that the infection was significantly related to age and breed. Capsular typing, using multiplex polymerase chain reaction (PCR), demonstrated that all strains were type A (100%). Disk diffusion assay towards ten antimicrobials revealed high susceptibilities to amikacin, doxycycline, chloramphenicol, and neomycin with varying degrees. Doxycycline was effective at the lowest concentration (MIC 0.125-1&#xa0;&#xb5;g/ml). Multidrug resistance was detected with a percentage of 25%. Multidrug-resistant isolates (five isolates) were subjected to study their pathogenicity in embryonated chicken eggs (ECE). The results showed a variation in indices between different dilutions of the tested strains. The resulting pathogenicity indices showed significant differences (P&#x2009;<&#x2009;0.05) according to the origin and dilution of the isolate. From the original inoculum to 10dilutions, the mortality of inoculated embryos occurred within 1-2&#xa0;days with pathological findings, including maceration and lesions on chorioallantoic membrane (CAM). From dilutions ranging from 10to 10, no death occurred until 7&#xa0;days post-inoculation, but a variation in the lesions on CAM was observed. In conclusion, P. multocida serogroup A could be intensely pathogenic for mature chickens thus causing considerable economic losses, and PCR provides a suitable technique for early and rapid diagnosis of fowl cholera.