The present invention relates to a certain microorganism for altering the composition of oral biofilms, in particular for use in the treatment and/or prevention of dental caries and/or periodontal disease. In particular, the present invention relates to a microorganism for use as a probiotic agent for altering the bacterial composition of oral biofilms derived from saliva, preferably for reducing the proportions of Gram-negative anaerobic genera and/or increasing the proportions of aerobic or facultatively anaerobic genera. Furthermore, the present invention provides oral pharmaceutical compositions, oral care products or products for nutrition or pleasure comprising the microorganism as probiotic agents as well as a method of production thereof.