Isolation and Molecular Detection of M. gallisepticum and F Strain like Isolates from Chicken Flocks Suffering from Respiratory Problems in Egypt

The study aimed to assess the possibility of molecular typing utilizing a gene exclusive to M. gallisepticum (MG) that encodes a phase-variable putative adhesion protein (PvpA). Based on size differences and nucleotide divergence of the C-terminus-encoding region, the pvpA PCR-RFLP assay was utilized to distinguish between vaccine F strains and M. gallisepticum isolates. The study found a high M. gallisepticum infection rate (66.6%, 100%, and 75.75%) in layer, broiler breeder, and broiler flocks, respectively, and a pvpA PCR-RFLP clarified that isolations were closely related to the vaccine F strain. The three M. gallisepticum isolates and the F-vaccine were evaluated for their pathogenicity and ability to spread in infected and in-contact chickens utilizing clinical symptoms, air sac lesions, PCR, and serological testing at 14 and 28 days after the experimental infection. Isolates sampled at the same time, in the same geographic area, and causing similar pathologic effects under field conditions revealed identical RFLP patterns and were closely situated in the phylogenetic development tree. The study found that in-contact birds in both vaccinated and infected groups showed positive PCR results at 14 days post-infection, indicating shedding and lateral transmission, and the immunity to M. gallisepticum field isolates and vaccination against the M. gallisepticum F strain was weak until 35 days post-infection. The study suggests that a pvpA PCR-RFLP assay can efficiently differentiate vaccine strains from field isolates, eliminating the need for culture isolation, and can also aid in the molecular epidemiology of M. gallisepticum epidemics by using sequence analysis or RFLP.