The present invention provides a protective formulation that prevents virulent Mycoplasma gallisepticum infection in birds of the order Galliformes. The formulation comprises a protective amount of live MG strain K5054 or derivatives thereof in a pharmaceutically acceptable carrier. A vaccine that prevents virulent Mycoplasma gallisepticum infection in birds of the order Galliformes is also presented. Methods for administering the formulation and vaccine are also presented.