Comparative assessment of a metabolically attenuated Mycoplasma gallisepticum mutant as a live vaccine for the prevention of avian respiratory mycoplasmosis

In a previous study, signature sequence mutagenesis (SSM) was used to identify a mutant with a disruption of the gene encoding the metabolic factor, dihydrolipoamide dehydrogenase, and that mutant was designated Mg 7. The current study assessed the safety, immunogenicity and efficacy of Mg 7 in comparison to two commercially available vaccines (ts-11 and F) as well as a Laboratory vaccine strain, GT5. Intratracheal vaccination of chickens with all four attenuated mutants induced varying levels of protection against intratracheal challenge with virulent Mycoplasma gallisepticurn strain R-low. Mg 7 vaccinated chickens rapidly cleared the challenge strain, had lower histopathologic tracheal lesion scores when compared to unvaccinated chickens, and mounted a strong humoral anti-M. gallisepticum-specific IgG response. The IgG levels increased 2- to 3-fotd upon R-low challenge. Mg 7 induced a greater level of protection against intratracheal R-low challenge than that observed with the other three attenuated strains, as evidenced by a lower recovery of R-low from tracheas and lower histopathologic lesion scores in tracheas and air sacs. Based on these findings, Mg 7 appears to have good potential as a safe and effective vaccine for the prevention of avian mycoplasmosis. (c) 2008 Elsevier Ltd. All rights reserved.