Antibiotypes of Bacteroides gingivalis assessed by antimicrobial disks and multivariate analysis.

Antibiograms with 20 different antimicrobial disks were studied for antibiotyping of Bacteroides gingivalis isolates. The stability of the antibiotypes was tested by passage in mice. Several B. gingivalis isolates of the same subject were used to investigate the presence of different antibiotypes in one individual, while isolates from different subjects were used to investigate individual differences. The antibiotypes were found to remain stable after animal passage. All tested strains of different origin represented different antibiotypes. The isolates from one subject all belonged to the same antibiotype. Principal component analysis of the data showed that two factors were important in the discrimination of the strains of B. gingivalis. One included beta-lactam antimicrobial agents that affect the cell wall. The other included antimicrobial agents that inhibit synthesis of protein and nucleic acid. Both principal component analysis and discriminant analysis proved to be of great use in the reduction of the amount of data and the visualization of the relations between different antibiotypes of B. gingivalis in a linear map. Among the investigated subjects, different antibiotypes of B. gingivalis were found, indicating that in the mouth of an individual, one antibiotype of B. gingivalis predominates and that different persons harbor different antibiotypes of B. gingivalis.