Most adults have bad breath occasionally, especially when we become dehydrated or after a full night sleep. Unfortunately, some have chronic foul breath. Solutions to the problem to date, has not been satisfactory as you can see with the myriad of over-the-counter preparations at the chemist. Regular teeth brushing, flossing, tongue scrapping or all sorts of mouthwashes can greatly improve one's breath but only for some hours at best.
During the 1960-70s, Dr. Tonzetich, a professor in the Faculty of Dentistry, University of British Columbia and his colleagues established that volatile sulfur-containing compounds were key identifiable gases in oral malodor. He helped organise international meetings on the subject of diagnosis and treatment of bad breath and was a founding member of the International Society for Breath Odor Research (there is such a society?).
Other researchers have identified around 150 different molecules in human breath, many of which offend the human nose: Rotten eggs (H2S -Hydrogen sulfide), Rotten cabbage (Methyl mercaptan (CH3SH)), Garlic (Allyl mercaptan (C3H6S) & Allyl methyl sulfide (C4H8S)), Fish (Dimethylamine (C2H7N) & Trimethylamine (C3H9N). These gases are waste products produced by the millions of bacteria feeding on food particles in the mouth. While gram +ve bacteria like strep mutans produces acid harmful to enamel, they are not heavy producers of foul smelling gases. Gram -ve organisms produce most of the malodorous gases but not one single bacterium is responsible.
Bacterial geneticists have identified about 1000 species of bacteria that happily inhabit the human mouth. Diet, stress levels, breathing patterns, illness, antibiotics and other factors can change the composition of this community and hence, the resultant aroma of the breath.
Many of the current treatments do not change the ecology of the oral cavity but may make it worse. Alcohol based and/or antiseptic based mouthwashes may the native bacteria making way for opportunistic species for infections. Some new mouthwashes go after the stink rather than the stinkers with ions of zinc or other metals that bind and neutralize sulfur compounds.
Mel Rosenberg at Tel Aviv Uni has developed a 2 phase oil/water rinse that temporarily reduces bad breath by sopping up some of the oral debris and microbes. Other teams are investigating whether probiotics rife with a gram-positive bacterial strain known as Streptococcus salivarius K12 can fight halitosis. A common resident of the mouth, K12 is benign and known to produce substances that deter harmful bacteria. At U.C.L.A., Shi et al are working on a mouthwash that contains a peptide tailored to selectively kill Strep. mutans and increase less malodorous microbes on the tongue.