Influence of abiotic factors on the bacteriocinogenic activity of Actinobacillus actinomycetemcomitans.

We evaluated the influence of abiotic factors on antagonistic activity of Actinobacillus actinomycetemcomitans strains isolated from periodontal pockets and two reference strains (ATCC 29523 and FDC Y4). Antagonistic assays were performed by the overlayer method on tryptic soy agar (TSA), brain heart infusion agar, thioglycollate agar and brucella agar, added with yeast extract and supplemented (S) or not with L-cystine and sodium bicarbonate. Iso-, auto-, and heteroantagonism against a wide range of indicator strains were assayed. The influence of incubation atmosphere (anaerobic chamber, anaerobic and candle jars) and pH (5.0 to 11.0) was also evaluated. Autoantagonism was not observed. TSA-S was shown to be the most adequate medium for antagonistic activity expression. The widest spectrum of heteroantagonistic activity was also observed on TSA-S. The incubation atmosphere affected only the isoantagonistic activity expression. Only at pH 8.0 did A. actinomycetemcomitans express bacteriocinogenic activity. The lack of standardized methodology to detect antagonistic activity can lead to discrepant results and can make data difficult to be compared. This study provides information on abiotic factors that influence bacteriocinogenic activity expression and suggests adequate culture conditions for testing A. actinomycetemcomitans bacteriocin production, contributing to the establishment of a reproducible and reliable methodology.

Bacteriocin production by Actinobacillus actinomycetemcomitans isolated from the oral cavity of humans with periodontal disease, periodontally healthy subjects and marmosets.

The ability of Actinobacillus actinomycetemcomitans to produce bacteriocin has rarely been reported. Antagonistic substance production may confer an important ecological advantage for the producer microorganisms, especially in a competitive ecosystem such as the oral cavity. In the present study, 75 A. actinomycetemcomitans strains isolated from the oral cavity of human patients with periodontal disease, periodontally healthy subjects and marmosets, as well as two reference strains (A. actinomycetemcomitans ATCC 29523 and FDC Y4) were evaluated for auto-, iso-, and heteroantagonistic activity. Fifty-one (68.00%) strains exhibited antagonistic activity; heteroantagonism was observed more often than isoantagonism. Isolated strains antagonized 17 different species of gram-positive and gram-negative bacteria from the oral and nonoral microbiota. Sensitivity to heat and to proteolytic enzymes constituted strong evidence that the antagonistic substance has a proteic nature. Taken together, our data enabled us to confirm that the antagonistic substance detected was a bacteriocin. The wide spectrum of activity indicates the possibility that more than one antagonistic substance is produced and that these substances play an important role in the ecological balance of the oral ecosystem.