[Methodological possibilities for in vitro evaluation of the antibiotic sensitivity of bacterial plaque from periodontal pockets].

Two different methods for making the subuletic bacterial antibiogram were compared, namely, the inhibition halo technique and that of percentage reduction. The first, of the more classical nature, is based on the introduction of the antibiotic inside a small cavity made in the culture medium, which leads to the formation of circular haloes around the cavity itself. The magnitude of the hales is all the greater, the more effective the antibiotic. The percentage-reduction technique calculates the reduction, expressed as a percentage, of the total number of colonies grown in the cultural medium containing the antibiotic, with respect to the number of colonies grown on a control culture-plate without antibiotic. Both techniques gave unambiguous results in 92.8% of the cases, both showing satisfactory validity; however, the percentage reduction technique proved to be more complex, to require fuller investigation and to be more expensive than the other. In fact, to make the antibiogram of a bacterial plaque concerning the seven antibiotics tested, 24 plates of agar-culture were necessary with the "r" method, whereas, with that of "inhibition haloes" only two sufficed. In addition, in the case of plaques with scarce microbial density or in the presence of highly invasive germs, by using the "inhibition haloes" method, it is always possible to have some information, which is impossible with the other method.