Objetivos: investigar los biotipos de S. mutans aislados de niños con y sin caries dentaly determinar su susceptibilidad antimicrobiana. Métodos: este estudio observacionaldescriptivo incluyó 206 niños entre los 3 y 5 años de dos preescolares en Bogotá, D.C., Colombia. Después de su aislamiento en agar Mitis Salivarius Bacitracina, lascepas S. mutans se identificaron por pruebas bioquímicas y se biotipificaron por elsistema api-ZYM. En todos los aislamientos se determinó por el método de diluciónenvagar la concentración inhibitoria mínima (CIM) de Penicilina, Amoxicilina, Cefazolina, Eritromicina, Clindamicina, Imipenem, Vancomicina y Teicoplanina.Resultados: Se encontró S. mutans en 30 de los 79 niños sin caries dental (38%) y en56 de los 127 niños con caries (44,1%). Los niños con caries presentaron un recuentosuperior de S. mutans en comparación con los niños sin caries (p 0,05). En totalse identificaron 121 cepas de S. mutans en los 86 niños: 43 cepas en los 30 niños sincaries dental y 78 en los 56 niños con caries dental. Las 121 cepas fueron agrupadasen 38 biotipos: 24 en el grupo de caries y 14 en el grupo sin caries. En el grupo decaries los biotipos más frecuentes fueron el XV, XI, XII y XVII, respectivamente,con 26, 12, 11 y 4 cepas y en el grupo sin caries los biotipos más frecuentes fueronel XXVI, XX y XXXVI, respectivamente, con 14, 8 y 7 cepas. Todos los biotiposObjectives: The main objective was to investigate the biotypes of S. mutans isolated from children with and without dental caries and determine its antimicrobial susceptibility. Methods: this descriptive observational study included 206 children aged 3 to 5 years of two preschool institutions in Bogota-Colombia. After isolation on agar Mitis Salivarius Bacitracin, S. mutans strains were identified by biochemical tests and biotyped by the api-ZYM system. The minimal inhibitory concentrations (MICs) of the S. mutans isolates were evaluated against penicillin, amoxicillin, cefazolin, erythromycin, clindamycin, imipenem, vancomycin and teicoplanin by an agar dilution method. Results: S. mutans was found in 30 of the 79 children without dental caries (38%) and in 56 of the 127 children with caries (44.1%). Children with cavities had a higher count of S. mutans compared to children without caries (p 0.05). A total of 121 strains of S. mutans were identified in 86 children: 43 strains in 30 children with dental caries and 78 in the 56 children with dental caries. The 121 strains were grouped into 38 biotypes: 24 in the group caries and 14 in the group without caries. In the group caries the most common biotypes were the XV, XI, XII and XVII, respectively, with 26, 12, 11 and 4 strains and the group caries the most common biotypes were the XXVI, XX and XXXVI, respectively, with 14, 8 and 7 strains. All biotypes were highly sensitive to all antimicrobials tested; 50 and 90% of S. mutans strains were inhibited by using concentrations lower than 0.12 and 1 µg/ml, respectively, for all antibiotics studied. The lowest MICs average values were obtained for penicillin, erythromycin and imipenem. Conclusions: In the study population a wide variety of biotypes was found, isolates were highly sensitive to antimicrobials evaluated and in each clinical group were identified unique patters that could indicate a specific colonization.