FISH/CLSM allowed the discrimination between S. sanguinis and P. gingivalis and determination of the relative proportions of all three species. A partially heterogeneous architecture of the biofilm, which may be due competitive binding, was observed. However, the distribution of the relative proportions of the three species in all experiments stayed unchanged. The heat flow at a given time (as determined using

IMC) was a measure of metabolic activities of all bacteria present, and it thus declines correspondingly if bacterial activity diminishes. Similarly, heat over time (i.e. the integral of the heat flow) is a proxy for the growth curve and approaches a maximum when metabolic activity decreases (Braissant et al., 2010). This metabolic decline and asymptotic biomass accumulation pattern is due to changes in the IMC ampoule internal see more environment that occur during bacterial metabolism; that is, exhaustion of available nutrients or electron acceptors or build up of metabolic waste products. The pattern of rise and decline of the metabolic activity of the biofilm was seen in the first 50 h (Fig. 3) exhibiting similarities in the behavior of the biofilm to common

Topoisomerase inhibitor liquid or solid culture studies (Braissant et al., 2010). Thus, cumulative heat correlates with cumulative bacterial biomass only during this early part when the biofilm still grows and until heat flow peak is reached. Once the heat flow has stabilized Ceramide glucosyltransferase at a constant level, the accumulation of heat is most probably not related to a net increase in bacterial numbers and production of fresh biomass, but, rather, to metabolic activities related to maintainance of the mature biofilm and survival of the present cells. Alternatively, it

can be hypothesized that during this steady state of the heat flow, growth rate is equal to bacterial death rate, resulting in a stable metabolically active bacterial population. This latter hypothesis is in line with the first one if equally low growth and death rates are considered. In the present study, between 72–480 h ca. 70% of the samples (n = 17) showed a low steady state heat flow comprised between 0.8 and 1.8 μW, whereas in the remaining 30% (n = 7), the values were found much higher (reaching from 8.6 to 86.0 μW). Assuming a heat flow of 2 pW per active bacterial cell (James, 1987), we calculated the number of active bacteria in the biofilm. This suggests that in the present samples showing the lowest steady state heat flow, ca. 4 × 105 to 9 × 105 bacteria remained active on the surface of the titanium disk (5 mm2), whereas this number is up to 4.3 × 107 in the samples having the highest heat flow. This result emphasizes major variability within biofilms that appear similar in microscopic analyses. On the other hand, the time required to reach the maximum heat flow showed only moderate specimen-to-specimen variability.