Atomic force microscopy study on specificity and non-specificity of interaction forces between Enterococcus faecalis cells with and without aggregation substance

Enterococcus faecalis is one of the leading causes of hospital-acquired infections, and indwelling medical devices are especially prone to infection. E faecalis expressing aggregation substance (Agg) adheres to biomaterial surfaces by means of positive cooperativity, i.e. the ability of one adhering organism to stimulate adhesion of other organisms in its immediate vicinity. In this study, atomic force microscopy (AFM) was used to measure the specificity and non-specificity of interaction forces between E faecalis cells with and without Agg. Bacteria were attached to a substratum surface and a tip-less cantilever. Two E faecalis strains expressing different forms of Agg showed nearly twofold higher interaction forces between bacterial cells than a strain lacking Agg [adhesive force (F-adh), -1(.)3 nN]. The strong interaction forces between the strains with Agg were reduced after adsorption of antibodies against Agg from -2(.)6 and -2(.)3 nN to -1(.)2 and -1.3 nN, respectively. This suggests that the non-specific interaction force between the enterococci amounts to approximately 1(.)2 nN, while the specific force component is only twofold stronger. Comparison of the results of the AFM interaction forces with the positive cooperativity after adhesion to a biomaterial in a parallel-plate flow chamber showed that in the absence of strong interaction forces between the cells, positive cooperativity was also absent. In conclusion, this is believed to be the first time that the influence of specific antibodies on interaction forces between E faecalis cells has been demonstrated by AFM, thereby experimentally distinguishing between specific and non-specific force components

Physico-chemical surface properties of oral streptococci

The importance of bacterial adhesion to solid substrata in various applications of environmentar, medical and industrial interest is pointed out in chapter 1 of this thesis. ... Zie: Summary

Weibull analyses of bacterial interaction forces measured using AFM

Statistically significant conclusions from interaction forces obtained by AFM are difficult to draw because of large data spreads. Weibull analysis, common in macroscopic bond-strength analyses, takes advantage of this spread to derive a Weibull distribution, yielding the probability of occurrence of a force value and the dependability of the data set. Here we propose Weibull distribution as a new way to present nanoscopic bacterial interaction forces obtained using AFM. (C) 2010 Elsevier B.V. All rights reserved