Antimicrobial properties of cyclodextrin-antiseptics-complexes determined by microplate laser nephelometry and ATP bioluminescence assay

Antimicrobial effects of substances can be determined with different methods that measure distinct parameters. Thus, a comparison of the results obtained can be difficult. In this study, two in vitro methods were employed to determine concentration and time dependent effects of cyclodextrin (CD)-complexes with the antiseptics chlorhexidine diacetate (CHX), iodine (IOD) and polihexanide (PHMB) on Candida albicans and Malassezia pachydermatis. Using both, microplate laser nephelometry and the ATP bioluminescence assay, it could be shown that CD-antiseptics-complexes tested exhibited significant antifungal effects with the exception of γ-CD-CHX in the case of C. albicans. Microplate laser nephelometry (MLN) is an optical method and enables a quantitative determination of particle concentrations in solution. By means of this method, microbial growth under influence of potential antimicrobial substances can be monitored over a prolonged time period. In addition, the antimicrobial activity was analyzed by measurement of the microbial adenosine triphosphate (ATP) content with a bioluminescent assay. The luminescent signal is directly proportional to the amount of ATP, and thus, a linear function of the number of living microbial cells present. Both methods were compared according to the half maximal inhibitory concentration (IC50) calculated and the statistical evaluation of Pearson's correlation coefficient (r). In summary, it could be demonstrated that both methods yield similar results although they differ in the parameter.