Microbiological and serological studies of Peptostreptococcus micros

Abstract

Peptostreptococcus micros, an anaerobic gram-positive coccus, has been associated with many polymicrobial infections at various locations of the human body, especially with periodontal and endodontic lesions of the oral cavity. Very little is known about the biology and pathogenicity of P. micros. In order to microbiologically characterize P. micros strains, the following studies were undertaken. P. micros was tested for its aerotolerance. P. micros was able to survive beyond 18 d of exposure to air losing only 2-4 logs in viability. A selective medium (PMM) for the primary isolation of P. micros was developed and evaluated. Using PMM, the prevalence of P. micros in periodontally diseased patients and the association of P. micros with halitosis patients were investigated. PMM was effective in differentiating 80 strains of P. micros from other oral microorganisms by the production of hydrogen sulfide after the utilization of glutathione resulting in a black precipitate directly under the colony. Significantly higher numbers and occurrences (P<0.05) of P. micros were isolated from the periodontal pockets of 12 adult or 18 early onset periodontitis patients than from healthy sites. In addition, P. micros was isolated from saliva, the surface of the tongue and supragingival plaque samples of 12 halitosis patients. The antibiotic susceptibility profiles of P. micros, detection of beta-lactamase and the effectiveness of mouthrinse products against P. micros were studied. Strains of P. micros tested were susceptible to 6 different antibiotics, higher MIC levels being observed with the cephems using three methods. There was no detectable beta-lactamase activity observed. A chlorhexidine gluconate mouthrinse solution inhibited the growth of P. micros. Hemolytic activity of P. micros was observed with only 2 out of 72 strains of P. micros tested. Using the CAMP test, the hemolytic activity of the P. micros strains was enhanced. P. micros attached to human buccal epithelial cells and to human, rabbit, horse, or sheep erythrocytes. The mechanisms involved in the coaggregation between P. micros and Fusobacterium nucleatum were studied. Coaggregation was inhibited by the addition of EDTA and 5 different amino acids but not by sugars. A higher affinity of coaggregation was observed between isolates of P. micros and F. nucleatum from the same periodontal lesions. All 21 human sera tested showed a positive reaction with P. micros by the dot-immunoblot assay. Cellular proteins of P. micros were separated using a 15% SDS-PAGE gel and the immunodominant antigens of P. micros and the subclass of human immunoglobulin G (IgG) reacting to these antigens determined. IgG2 was the major human IgG subclass reacting with the immunodominant antigens. The high aerotolerance, distribution throughout the human oral cavity, ability to attach to erythrocytes and human buccal epithelial cells and to coaggregate with F. nucleatum participate in allowing of P. micros to be involved in oral disease processes. (Abstract shortened by UMI.)