What causes bad breath in dogs?

According to a team of researchers from the Forsyth Institue in Boston and the University of Michigan School of Dentistry, they have found the same three bacteria common among five people with fresh breath; the most common being Streptococcus salivarius. This "good" germ did appear in one of six people with halitosis (foul breath), but in that case it was only in low levels. Sources: http://www.bio-medicine.org/medicine-news/Germs-to-blame-for-bad-breath-1895-1/ http://abcnews.go.com/Health/Dental/story?id=119221