Evaluation of three selective media for isolation of Aggregatibacter actinomycetemcomitans.

BACKGROUND AND OBJECTIVE: Aggregatibacter actinomycetemcomitans is a pathogen in oral and nonoral infections. Detection and quantification of this pathogen can be performed using selective culture techniques. The aim of this study was to establish the efficacy of two known selective media in their ability to select and support the growth of A. actinomycetemcomitans. MATERIAL AND METHODS: Trypticase soy bacitracin vancomycin (TSBV) medium and brain-heart infusion agar with vancomycin (Dentaid-1), as well as a modified Dentaid-1 medium (in which the brain-heart infusion agar was substituted with brain-heart infusion broth), were compared. Two-hundred and eighteen clinical samples were used to establish the recovery rate, the number of colony-forming units (CFUs) of A. actinomycetemcomitans as well as the total number of CFUs on the three different types of medium. In addition, the numbers of gram-negative aerobic rods and yeasts were determined. RESULTS: Both types of Dentaid-1 medium showed a higher recovery of A. actinomycetemcomitans compared with TSBV. However, these differences did not reach statistical significance. The total number of CFUs of A. actinomycetemcomitans recovered was significantly higher on Dentaid-1 compared with TSBV (p = 0.029). The mean number of gram-negative aerobic rods recovered was statistically higher on both types of Dentaid-1 medium in comparison with TSBV. Low numbers of yeasts were recovered occasionally on all test plates. CONCLUSION: Dentaid-1 is a low-cost effective alternative to TSBV for the isolation and growth of A. actinomycetemcomitans from clinical samples, such as dental plaque, which contain a complex microflora.

Antibiotic susceptibility profiles of oral pathogens.

Periodontitis is a bacterial disease that can be treated with systemic antibiotics. The aim of this study was to establish the antibiotic susceptibility profiles of five periodontal pathogens to six commonly used antibiotics in periodontics. A total of 247 periodontal bacterial isolates were tested for susceptibility to the six antibiotics using the Etest method. MIC(50) and MIC(90) values (minimum inhibitory concentrations for 50% and 90% of the organisms, respectively) were calculated. Both European Committee on Antimicrobial Susceptibility Testing (EUCAST) and Clinical and Laboratory Standards Institute (CLSI) breakpoints were used in the study to interpret results. ß-Lactamase production was tested when amoxicillin resistance was found. MIC(90) values of the anaerobic bacteria were all well below breakpoint values, except for three isolates of Prevotella intermedia and one isolate of Fusobacterium nucleatum that were resistant to amoxicillin (CLSI breakpoints); these isolates were ß-lactamase-positive. Two isolates of the capnophilic Aggregatibacter actinomycetemcomitans appeared to be amoxicillin-resistant but failed to show ß-lactamase activity. Comparison with a previous study from The Netherlands showed minor differences in susceptibility profiles, but the MIC(90) values of A. actinomycetemcomitans for amoxicillin, clindamycin, azithromycin and tetracycline were higher. Geographical differences in the susceptibility profiles of Porphyromonas gingivalis and A. actinomycetemcomitans between European countries were noted. Comparison of European susceptibility profiles with that of a South American country (Colombia) revealed a much higher resistance in the latter. Owing to these differences in susceptibility profiles, it is of concern to regularly perform surveillance studies on antibiotic resistance.