According to Danish researchers, certain probiotic gums like Lactobacillus reuteri can reduce bad breath. The two stains of L. reuteri produce reuterin in presence of glycerol. The study is done on a small scale and further study is required on the same. Although the benefits are less but because of these benefits the pro-biotic gums are used by mouthwash brands to maintain a healthy oral hygiene.

Via: http://www.nutraingredients.com/Research/Probiotic-gum-beats-placebo-for-bad-breath-Study

According to the research, some bacteria in our mouth cause bad breath while others protect from bad breath. The research was published in the Journal of Clinical Microbiology. The study was based on gene sequencing. For this study, different bacterias on the tongue are compared for bad breath and fresh breath. According to the researchers, the most common bacteria is Streptococcus salivarius, which affects one out of six people with bad breath. Factors such as blood group can be responsible for the prevalence of sulfurous bacteria, thereby causing halitosis.

Via: http://abcnews.go.com/Health/Dental/story?id=119221#.T14kETx4B9E

Dr Harold Katz of California Breath Clinic worked on halitosis and explained that the major cause of halitosis is a bacteria which is present in our mouth and throat. Anaerobic sulphur producing bacteria is the one that is responsible for digestion. The increased number of these bacteria often cause bad breath. These bacteria on combining with sulphur rich compounds like cysteine and methionine, produce smelly sulfurous compounds.

Via: http://www.therabreathcanada.com/research_truth.asp