A Mycoplasma gallisepticum (MG) isolate from an atypically mild outbreak in turkey breeders was found to be similar to house finch isolates by DNA analyses. A preliminary study in turkeys showed that this isolate (K5054) caused very mild lesions and protected turkeys against subsequent challenge with a virulent MG strain. The safety and efficacy of K5054 was further evaluated in commercial layer-type chickens and turkeys; there was evidence of protection from lesions associated with MG and reduced isolation of R strain post challenge in vaccinated birds. K5054 was further characterized for stability following in vivo passages through chickens; the persistence and the duration of immunity elicited by a single vaccination; and the transmissibility to unvaccinated chickens. K5054 has shown promise as a safe, efficacious, stable vaccine with relatively low transmissibility and long persistence and duration of immunity. In another study, MG isolates from the USA, Israel and Australia were characterized by random amplified polymorphic DNA (RAPD) analysis as well as DNA sequence analysis of portions of the phase-variable putative adhesin protein (pvpA) gene, the cytadhesin gapA gene and an uncharacterized lipoprotein (LP) sequence. The results were compared to reference strains (vaccine and laboratory strains). The RAPD analysis and combined DNA sequence analysis data correlated well, although sequence analysis of any one of the genes did not result in definitive identification of isolates. The Australian isolates appeared to be more similar to the US isolates than were the Israeli isolates.