DEVELOPMENT AND EVALUATION OF A SELECTIVE AND DIFFERENTIAL MEDIUM FORTHE PRIMARY ISOLATION OF PEPTOSTREPTOCOCCUS-MICROS

Peptostreptococcus micros, an anaerobic gram-positive coccus, has been associated with periodontal and endodontic lesions, including those r efractory to treatment, as well as many human polymicrobial infections in other body locations. A selective and differential medium for the primary isolation of P. micros was developed and evaluated. Columbia C NA agar, a selective medium for gram-positive cocci, was supplemented with glutathione and lead acetate (P. micros medium: PMM). P. micros h as a characteristic of rapidly utilizing the reduced form of glutathio ne to form hydrogen sulfide, which reacts with lead acetate producing a black precipitate in the medium. When grown on PMM, P. micros can be easily identified by its typical colonial morphology and the presence of a black precipitate directly under the colony. PMM was compared fo r the growth of P. micros with phenylethyl alcohol agar (PEA) and Colu mbia base medium (CBM) with 80 strains of P. micros and 30 strains of other gram-positive cocci. All P. micros isolates tested grew and show ed the typical morphology of P. micros on PMM. Using colony counts on CBM as controls, there was an average 81.8% recovery in the number of P. micros colonies on PMM, in contrast to an average 6.1% recovery on PEA. Subgingival plaque and tongue samples from 12 adult periodontitis and 6 early-onset periodontitis patients were cultured onto PMM for t he isolation of P. micros. P. micros was isolated on PMM and identifie d biochemically and enzymatically from both adult periodontitis and ea rly-onset periodontitis patients with higher percentages isolated from the diseased periodontal pockets of adult periodontitis patients; fur thermore, this is the first isolation of P. micros from tongue samples taken from periodontally diseased patients. This medium in cultural s tudies will further our understanding and assist future investigations of P. micros involved in disease processes.