Fimbrial-mediated colonization of murine teeth by Actinomyces naeslundii

Groups of mice fed diets high in sucrose or glucose were orally inoculated with 10(10), 10(9) or 10(8) colony-forming units of one of the following Actinomyces naeslundii strains possessing the type 1 (T1+) and/or the type 2 (T2+) fimbriae: T14VJ1 (T1+, T2+), 5519 (T1+), 5951 (T2+), and 147 (non-fimbriated). Ninety-six hours after inoculation their upper jaws were cultured to look at the implantation of each of these strains on the teeth. In mice fed a sucrose diet, regardless of the presence or absence of fimbriae, each bacterial strain colonized 100% of the mice at the highest inoculation doses of the infecting organism. But at a dose of 10(8), T14V-J1 was the only strain which colonized 100% (12/12) of the mice, 5519 colonized 10/11, 5951 colonized 9/11 and 147 colonized 7/11. These differences were not statistically significant. When mice were fed a high-glucose diet, 100% infection was achieved with strains T14V-J1, 5519 and 5951 only at the highest dose of 10(10) colony-forming units. Strain 147 colonized in 8/9 of the mice at that dosage. At lower dosages, no bacterial strain implanted in 100% of the mice. In the glucose experiment at a dose of 10(8), strains expressing the T1 fimbriae implanted significantly better than strains without the T1 fimbriae. At a dose of 10(9) colony-forming units, the parent strain T14V-J1 implanted significantly better than strains without the T1 fimbriae. Similarly, strain 5519 (T1+) implanted significantly better than 5951 and implanted better than 147, although the difference was not significant. These results suggest that while the presence of the T1 and T2 fimbriae may confer some advantage in the establishment of these organisms in vivo, even the strains without fimbriae were able to colonize. Strains T14VJ1 and 5519 were found to bind well to hydroxyapatite treated with mouse saliva, while strains 5951 and 147 did not. Only T2 fimbriated strains T14V-J1 and 5951 exhibited a lactose-reversible coaggreation with indigenous strains of enterococci that may contribute to the elevated levels of colonization of strain 5951 in vivo.