Genetic comparison of the Mycoplasma gallisepticum 6/85 vaccine strain and 6/85-like field isolates

Authors: Leigh, Spencer; Evans, Jeffrey - Jeff

Submitted to: Veterinary Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/19/2024
Publication Date: 2/15/2024
Citation: Leigh, S.A., Evans, J.D. 2024. Genetic comparison of the Mycoplasma gallisepticum 6/85 vaccine strain and 6/85-like field isolates. Veterinary Microbiology. 291(2024), 110008. https://doi.org/10.1016/j.vetmic.2024.110008.
DOI: https://doi.org/10.1016/j.vetmic.2024.110008

Interpretive Summary: Live attenuated vaccines strains are the most effective means of controlling Mycoplasma gallisepticum infection and presenting disease symptoms in poultry species. However, field isolates with the potential to cause disease have been isolated that have genetic markers consistent with those isolates being identical to the live attenuated vaccine strains. Genomes sequencing of the strain allowed for identification of genetic markers that can be used to differentiate the strains. Analysis identified that the majority and potentially all these vaccine-like strains are separate from the vaccine strain instead of being derived from the vaccine strain. This strengthens the understanding of the safety of the vaccine strains and answers concerns that poultry producers may have about these vaccines causes disease.

Technical Abstract: Mycoplasma gallisepticum infection in poultry leads to disease and pathology that can reduce producer profits. Live attenuated vaccines are available that can limit or completely prevent the effects of infection. Field isolates that are genetically related to the attenuated vaccine strains have been isolated, raising the question of whether the attenuation of the vaccine strains is limited and can lead the strains to revert to more virulent forms. The 6/85 live attenuated vaccine is derived from a field isolate collected in the United States. Analysis of the genome of sequenced M. gallisepticum strains revealed a cluster of 10 6/85 like strains that group with the 6/85 vaccine strain. Four genomic regions were identified that allowed for strain differentiation. The genetic differences between strains points toward 9 of the 10 strains most likely being sister strains to the 6/85 vaccine strain. Insufficient differences are present in the tenth strain to make a definitive conclusion. These results suggest that most if not all strains similar to the live attenuated vaccine strain are field isolates of the parent strain used to derive the live attenuated vaccine.