The Extracellular Matrix Component Psl Provides Fast-Acting Antibiotic Defense in Pseudomonas aeruginosa Biofilms

Bacteria within biofilms secrete and surround themselves with an extracellular matrix, which serves as a first line of defense against antibiotic attack. Polysaccharides constitute major elements of the biofilm matrix and are implied in surface adhesion and biofilm organization, but their contributions to the resistance properties of biofilms remain largely elusive. Using a combination of static and continuous-flow biofilm experiments we show that Psl, one major polysaccharide in the Pseudomonas aeruginosa biofilm matrix, provides a generic first line of defense toward antibiotics with diverse biochemical properties during the initial stages of biofilm development. Furthermore, we show with mixed-strain experiments that antibiotic-sensitive “non-producing” cells lacking Psl can gain tolerance by integrating into Psl-containing biofilms. However, non-producers dilute the protective capacity of the matrix and hence, excessive incorporation can result in the collapse of resistance of the entire community. Our data also reveal that Psl mediated protection is extendible to E. coli and S. aureus in co-culture biofilms. Together, our study shows that Psl represents a critical first bottleneck to the antibiotic attack of a biofilm community early in biofilm development.National Institutes of Health (U.S.). National Institute of Environmental Health Sciences (Training Grant in Toxicology 5 T32 ES7020-37

Transport of Particles in Intestinal Mucus under Simulated Infant and Adult Physiological Conditions: Impact of Mucus Structure and Extracellular DNA

The final boundary between digested food and the cells that take up nutrients in the small intestine is a protective layer of mucus. In this work, the microstructural organization and permeability of the intestinal mucus have been determined under conditions simulating those of infant and adult human small intestines. As a model, we used the mucus from the proximal (jejunal) small intestines of piglets and adult pigs. Confocal microscopy of both unfixed and fixed mucosal tissue showed mucus lining the entire jejunal epithelium. The mucus contained DNA from shed epithelial cells at different stages of degradation, with higher amounts of DNA found in the adult pig. The pig mucus comprised a coherent network of mucin and DNA with higher viscosity than the more heterogeneous piglet mucus, which resulted in increased permeability of the latter to 500-nm and 1-µm latex beads. Multiple-particle tracking experiments revealed that diffusion of the probe particles was considerably enhanced after treating mucus with DNase. The fraction of diffusive 500-nm probe particles increased in the pig mucus from 0.6% to 64% and in the piglet mucus from ca. 30% to 77% after the treatment. This suggests that extracellular DNA can significantly contribute to the microrheology and barrier properties of the intestinal mucus layer. To our knowledge, this is the first time that the structure and permeability of the small intestinal mucus have been compared between different age groups and the contribution of extracellular DNA highlighted. The results help to define rules governing colloidal transport in the developing small intestine. These are required for engineering orally administered pharmaceutical preparations with improved delivery, as well as for fabricating novel foods with enhanced nutritional quality or for controlled calorie uptake