Peptostreptococcus micros smooth and rough genotypes in periodontitis and gingivitis

Background: Two genotypes can be distinguished within the species Peptostre ptococcus micros: a smooth (Sm) and a rough (Rg) type. To date no systemati c study has been performed on the prevalence and proportion of both types i n untreated periodontitis patients and subjects without destructive periodo ntal disease. Therefore, the present study was performed to investigate: 1) the relative importance of the Sm and the Rg genotype of P. micros in peri odontitis and gingivitis; 2) the correlation between smoking and the 2 geno types of P. micros; and 3) the systemic antibody response against the 2 gen otypes in relation to the periodontal condition and smoking. Methods: A total of 104 untreated periodontitis patients and 41 individuals with gingivitis underwent clinical examination and microbiological samplin g. Pocket samples were cultured anaerobically on blood agar plates to deter mine the prevalence and proportion of the Sm and Rg types of P. micros. Ser um antibody titers against both types of P. micros were determined in all s ubjects by enzyme-linked immunosorbent assay (ELISA) using whole bacterial cells as antigen. Additionally, in a representative group of subjects, the antigen specificity of the serum antibodies was assessed by immunoblotting experiments. Results: The prevalence of the Sm genotype was higher in subjects with peri odontitis (94%) compared to subjects with gingivitis (59%), whereas the pre valence of the Rg type was not significantly different (38% versus 29%). Si milar analyses were performed for subgroups of smokers and non-smokers; wit hin the periodontitis group, the prevalence of the Sm type was not differen t between smokers and non-smokers (96% and 92%, respectively), whereas the prevalence of the Rg type was higher in smokers (48%) compared to non-smoke rs (19%). No difference in prevalence of both types was observed between sm okers and non-smokers within the gingivitis group. The titers and specifici ty of P. micros-specific immunoglobulins in periodontitis patients were not different from those in gingivitis subjects, nor were they related to smok ing status or culture-positivity. Conclusions: The results of this study suggest that both the Sm and the Rg genotypes of P. micros are part of the normal oral microbiota. However, the elevated prevalence of the Sm genotype in periodontitis and the elevated p revalence of the Rg type in periodontitis patients who smoke implies that b oth types can behave as opportunistic pathogens in destructive periodontal disease.