Streptococcus mutans is believed to be the principal etiologic agent of dental caries (3, 15). Most strains of S. mutans produce mutacins (bacteriocins), which are antimicrobial substances that inhibit the growth of closely related species (9, 26) as well as other gram-positive bacteria (26). The role of mutacins in vivo is unknown; however, the antimicrobial activity of these substances may confer an ecologic advantage for the producing strain in bacterial communities such as the dental biofilm (3). Mutacins may also be important for the establishment of S. mutans in vivo (3, 10). Several studies suggested that the mutacin activity of S. mutans can be related to the prevalence of this species in the bacterial biofilm, saliva and dental caries (4, 12, 23), increasing the risk of caries (9). Fabio et al. (7) demonstrated that mut- acin production can increase the propor- tion of S. mutans in oral streptococci. However, Alaluusua et al. (2) and Longo et al. (16) did not find any positive corre- lation between mutacin production and caries activity. The possible association between the biodiversity of S. mutans and caries activity deserves further study because the scarce literature has reported contra- dictory data about the impact of the genetic/phenotypic diversity of cario- genic species in the development and progress of dental caries (1, 13). Studies of virulence factors of S. mutans, as well as the mutacin production and its correlation with species biodiversity, are Oral Microbiology Immunology 2005: 20: 20–24 Printed in Singapore. All rights reserved Copyright Ó Blackwell Munksgaard 2005 Mutacin production in Streptococcus mutans genotypes isolated from caries-affected and caries-free individuals Kamiya RU, Napimoga MH, Rosa RT, Ho ¨fling JF, Gonc ¸alves RB. Mutacin production in Streptococcus mutans genotypes isolated from caries-affected and caries-free individuals. Oral Microbiol Immunol 2005: 20: 20–24. Ó Blackwell Munksgaard, 2005. Relationships between genetic diversity and mutacin production in Streptococcus mutans were evaluated in 319 clinical isolates from eight caries-affected and eight caries-free individuals. The isolates were submitted to mutacin typing and AP-PCR (arbitrarily primed polymerase chain reaction) assay. The mutacin production was detected for 12 Streptococcus sp. indicator strains. Results showed significant variations in the mutacin production profiles and the inhibitory spectra of both groups. A possible association was seen between mutacin activity and the distinct patterns of Streptococcus sp. colonization in the two groups. Genotyping by AP-PCR using the primers OPA-02 and OPA-13 revealed 101 distinct genotypes against 48 phenotypes identified by mutacin typing. No correlation was observed between the inhibitory spectra of mutacin and genotypic similarities based on AP-PCR analyses. According to our results, strains of the same S. mutans genotype showed different mutacin profiles, suggesting a high degree of interstrain diversity. In conclusion, mutacin production seems to be of clinical importance in the colonization of S. mutans and is highly diversified in the S. mutans species. R. U. Kamiya, M. H. Napimoga, R. T. Rosa, J. F. Ho ¨ fling, R. B. Gonc ¸ alves Microbiology and Immunology Laboratory, Dentistry School of Piracicaba, State University of Campinas, Brazil Key words: AP-PCR; dental caries; geno- typing; mutacin; Streptococcus mutans Reginaldo Bruno Gonc ¸alves, Microbiology and Immunology Laboratory, Dentistry School of Piracicaba, State University of Campinas, Brazil E-mail: reginald@fop.unicamp.br Accepted for publication September 1, 2004