MG is upper respiratory.  it creates the foamy exudate in eyes.  
treatment:  Outbreaks of MG can be controlled with the use of antibiotics. Erythromycin, tylosin, spectinomycin, and lincomycin all exhibit anti-mycoplasma activity and have given good results. Administration of most of these antibiotics can be by feed, water or injection. These are effective in reducing clinical disease. However, birds remain carriers for life. 
the foam is probably coming from sinus duct.  you need the antibiotic to go systemically through the body or airsacculitis will develop.  watch for a caseous buildup in the eye.  it is called "cheese."  nasty yellowish stuff made of white blood cells i think.  
our vet gave us eye ointment as well but you need to make sure the drug circulates throughout the body (oral dosing).