The diffusion of beta-lactam antibiotics through mixed gels of cystic fibrosis-derived mucin and Pseudomonas aeruginosa alginate.

The rates of diffusion through purified extracellular alginate from Pseudomonas aeruginosa were measured for twelve beta-lactam antibiotics. The diffusion rate was reduced as the antibiotic molecular weight increased, but the range of diffusion rates exhibited by a common anti-pseudomonal penicillins was relatively small. The diffusion of ticarcillin through 1.0% w/v mixtures of alginate and purified mucus glycoprotein (mucin) from sputa of cystic fibrosis patients showed that, at equivalent concentrations, alginate represented the greater barrier to penetration. However if the mucin concentration was increased to 4.0% w/v, a more realistic physiological concentration, the diffusion of ticarcillin was retarded to a greater extent than in 1% w/v alginate, and the effect was compounded by other sputum components such as DNA. The results suggest that the antibiotic diffusion barrier represented by mucin may be significant in vitro, particularly for nebulized antibiotics.