Antimicrobial activity of beta-lactam antibiotics against clinical pathogens after molecular inclusion in several cyclodextrins. A novel approach to bacterial resistance.

Recognition and uptake by specific cellular receptors and transport systems for cyclodextrins have been demonstrated. Based on this concept, natural and synthetically modified cyclodextrins were used as drug carriers. Several beta-lactam antibiotics were selected and their inclusion complexes with different cyclodextrins were prepared (molar ratio ranging from 1:1 to 1:3). The complex formation, in aqueous solution, was monitored and optimum complexation conditions were selected. The inclusion of the active molecules in the cyclodextrin cavity was confirmed by (1)H NMR spectroscopy. Specific HPLC methods for the quantitation of antibiotics in the presence of cyclodextrins were developed and their chemical stability under complexation conditions was confirmed. Antimicrobial activity of drug-cyclodextrin complexes, in terms of minimum inhibitory concentration (MIC), were compared with the corresponding values of uncomplexed free molecules. A wide range of clinical pathogens and known beta-lactamase-producing strains were tested. The activity of the cyclodextrin-included antibiotics was increased, particularly against Gram-negative clinical strains. The nature and degree of substitution on cyclodextrin macromolecules may be the predominant factor in the observed improvement in antimicrobial activity. We believe that the proposed methodology is a novel approach to the microbial resistance problem and will trigger research towards the development of new cyclodextrin derivatives bearing the ability to increase the uptake of included antimicrobial molecules through intensification of the corresponding molecular recognition phenomena.