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

Abstract

Cyclodextrins (CDs) are able to form inclusion complexes with other molecules, thereby, protecting these guest molecules from degradation, enhancing their biocompatibility or influencing their physiological distribution while retaining their activity. Here, antibacterial effects of CD-complexes with the antiseptics chlorhexidine diacetate (CHX), iodine (IOD) and polihexanide (PHMB) were determined using two different in vitro methods, microplate laser nephelometry and an ATP bioluminescence assay. Laser nephelometry is a direct method for monitoring and evaluating growth of micro-organisms by measurement of the turbidity of the solution. In contrast, the ATP bioluminescence assay determines specifically the amount of metabolic active bacterial cells. The antibacterial effects of CD-antiseptics-complexes were examined for Escherichia coli, Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus and Staphylococcus epidermidis and the results of both methods were compared in respect of calculated means of half maximal inhibitory concentrations (IC50) and statistical evaluated Pearson's correlation coefficients (r). It could be demonstrated that both methods showed a high comparability although they differ in the parameters tested. This study revealed that CD-complexes with CHX and PHMB were most effective against E. coli and the tested staphylococci. While CD-IOD-complexes obtained high activity against K. pneumoniae, P. aeruginosa was distinctly more resistant compared to the other bacteria.