© 2016 Functional Foods in Health and Disease. All rights reserved.Background: Fusobacterium spp. are known to be part of mouth and intestinal microbiota. Fusobacterium nucleatum is an obligate anaerobe, Gram negative, non-spore forming pleomorphic bacillus that can cause diseases not only in the mouth and teeth but also in the brain, pleura, lungs and liver. It was noted that F. nucleatum induces fetal death (fetal demise) in pregnant women. Recent studies indicate that F. nucleatum could lead to colon cancer by binding to the epithelial tissue. Kefir is produced from kefir grains that are a source of probiotics. Fermented dairy products and especially kefir and yogurt are significant for functional nutrition. In kefir grains, lactic acid bacteria, acetic acid bacteria and yeasts are embedded in a polysaccharide matrix, called kefiran. When kefir grains are added to milk and incubated for approximately 22 h at 25°C, microorganisms in the grains continue to proliferate in milk with the production of functional metabolic compounds. While yogurt has mainly two bacteria, authentic kefir has its characteristic Lactobacillus kefiranofaciens, Lactobacillus kefir and Lactobacillus kefirgranum, in addition to many other types of lactic acid bacteria (LAB). Previous studies have indicated that fermented dairy products can cause probiotic effects such as improvement in digestive system health, reduction in serum cholesterol, improvement in lactose tolerance, improvement in immune function, control of irritable bowel symptoms, and anticarcinogenic properties. Objective: The aim of this research was to report the effects of fermented dairy products in vitro on the growth of F. nucleatum. Milk, kefir made from natural kefir grains, commercial kefir produced from kefir starter culture, yogurt produced from natural yogurt starter culture and commercial yogurt produced from yogurt starter culture were used against F. nucleatum. Methods: F. nucleatum (ATCC 25586) was grown in Fluid Thioglycollate Medium at 37°C for 3 days under anaerobic incubation. Kefir was made from authentic kefir grains with 2% by volume inoculation at 25°C for 22h fermentation. Yogurt was made using a natural starter culture. The inhibition effects of fermented dairy products were determined in vitro against F. nucleatum. Zone inhibition tests were conducted using sterile disks that were immersed into kefir and yogurt samples and subsequently placed on Brucella Blood Agar with Hemin and Vitamin K1 inoculated with F. nucleatum; plates were incubated at 37°C for 3 days under anaerobic conditions. Inhibition zones were determined after the incubation was completed. Additionally, lactic acid bacteria (counted on MRS and m17), yeast (PDA) and related pathogen were observed after anaerobic incubation by adding a certain amount of kefir and yogurt cultures into F. nucleatum inoculated medium. Results: Authentic kefir samples exhibited distinct inhibitory zone against F. nucleatum after incubation agar plates. The largest zone of inhibition (with 9.5 mm) was caused by natural kefir samples made from kefir grains. Yogurt samples provided 8.25 mm zone inhibition against F. nucleatum. The milk used to make kefir and yogurt did not cause any zone of inhibition. It was also discovered that number of F. nucleatum in Thioglicollate Medium decreased depending on inoculated concentrations of kefir and yogurt cultures. Conclusion: Kefir is known to have positive effects on health and especially intestinal health. Therefore, these findings are important for showing an inhibition effect of fermented dairy products against a pathogen and possible carcinogen. These results suggest that regular consumption of natural fermented dairy products especially kefir should be included in a functional diet. The impact of these cultured dairy products could be promising and warrants further investigation with in vivo studies.