Switch Phenotypes of Peptostreptococcus micros and Susceptibility to beta-defensins

Peptostreptococcus micros is a Gram-positive, aerotolerant anaerobe associated with periodontal diseases. P. micros displays two colony morphotypes: a smooth colony and a rough colony with wrinkled edges. We previously demonstrated that phenotypic switching occurred spontaneously and reversibly. Objectives: The purposes of this study were: 1) to evaluate whether switch phenotypes occur in vivo in association with chronic periodontal disease and 2) to assess the susceptibility of the switch phenotypes to beta-defensins, antimicrobial peptides produced in the oral cavity. Methods: Bacterial sampling was performed for four diseased and two healthy sites by paper points from two subjects with chronic periodontal disease. The samples were plated on PMM and blood agar plates. P. micros colonies were selected based on growth profile on the PMM agar and Gram staining. They were also grown on BHIN agar to determine colony morphology and reversibility of the phenotype. Confirmation of P. micros was done by extracting the DNA and using P. micros specific primers in a PCR assay for species identitification. P. micros isolates were also genotyped by AP-PCR. Susceptibility of the phenotypes to HBD2 and HBD3 was determined with a Radial Diffusion Assay. Results: Both phenotypes were present in both subjects with 59% of those isolated being smooth and 41% rough. The smooth phenotype was more susceptible to the beta-defensins than the rough phenotype (P = 0.0299 for HBD2 and 0.057 for HBD3). The P. micros rough phenotype was significantly more susceptible to HBD2 than HBD3. Switching of the phenotypes was reversible after subculture. Conclusions: This study demonstrates the in vivo phenotypic switching of P. micros, and the fact that phenotype can impact susceptibility to innate antimicrobial agents. Thus, phenotypic switching by P. micros could be an important virulence factor implicating its role in periodontal diseases progression.