Streptococcus faecalis and Streptococcus faecium in infected dental root canals at filling and their susceptibility to azidocillin and some comparable antibiotics.

The study was performed on 612 routine cultures of material obtained from root canals of teeth at the time of filling (r-cultures) by students at the Department of Endodontics during a continuous period of one year. Twenty-nine isolates from 27 (29.3%) of the 92 positive cultures filled the criteria of enterococci (Sherman, 1937) and had demonstrable group D-antigen. With a set of tests these isolates were identified as follows: Strep. faecalis subsp. faecalis (10), Strep. faecalis subsp. zymogenes (3), Strep. faecalis subsp. liquefaciens (8), atypical variants of Strep. faecalis (6), Strep. faecium var. faecium (1) and Strep. faecium var. durans (1). Five tests in the present study clearly differentiated Strep. faecalis from Strep. faecium i.e. fermentation of sorbitol, glycerol (anaerobic) and melezitose, tolerance to potassium tellurite (0.1%) (positive for Strep. faecalis) and production of hydrogen peroxide (positive for Strep. faecium). In the inocula 10(3) or more colony forming units of enterococci were found more often of other identified microorganisms. This means that enterococci are of special interest in studies on the influence of infection at the time of filling of root canals on the prognosis of root canal therapy. The isolates were also tested for susceptibility to azidocillin, ampicillin, penicillin-G, penicillin-V and erythromycin with the paper disc method. All the isolates were susceptible to azidocillin and ampicillin (sensitivity group I), while the majority of the isolates showed a lower susceptibility to the other three antibiotics (sensitivity group II). The significance of these findings in the choice of prophylactic antibiotic to prevent bacterial endocarditis in patients with a history of rheumatic or congenital heart disease are discussed, when bacteremia from dental procedures may be expected.