Antagonistic interactions among Fusobacterium nucleatum and Prevotella intermedia with oral lactobacilli

Microbiota residing in oral ecosystems show great complexity because of the mutual interdependence of certain microorganisms that might influence their presence or absence at a given site. The aim of this work was to evaluate possible antagonistic interactions among Fusobacterium nucleatum and Prevotella intermedia, isolated from periodontal pockets, and Lactobacillus casei, L. salivarius, L. rhamnosus and L. plantarum isolated from saliva. Different tests were carried out using each strain as an effector as well as a sensitive strain, alternatively: (1) agar diffusion with paper disks embedded with supernatants and pellets in different culture media; (b) the well diffusion assay; (c) the double layer method; and (d) OD(560) measurements of the kinetic growth of Lactobacillus strains in LAPTg broth with different volumes of F. nucleatum supernatant. P. intermedia supernatant did not have an inhibitory effect on Lactobacillus growth, except for L. casei, when the double plaque method was used. F. nucleatum supernatant inhibited growth of all Lactobacillus strains when the well diffusion method was used. F. nucleatum inhibited L. casei growth whatever the method used. The substance responsible for inhibition was a thermoresistant extracellular protein which was hydrolyzed by trypsin-like proteases. None of the species of lactobacilli studied inhibited the growth of P. intermedia or F. nucleatum.