Adhesion of Pseudomonas aeruginosa pilin-deficient mutants to mucin.

Attachment of Pseudomonas aeruginosa to epithelial cells or tracheobronchial mucin is mediated by surface adhesins. Pili, composed of monomeric pilin subunits, make up one such class of adhesins. The formation of pili and flagella in P. aeruginosa is under the control of the alternative sigma factor rpoN. Isogenic mutant strains with insertionally inactivated rpoN genes were constructed with strains PAK, 1244, and CF613 and were tested for their ability to adhere to respiratory mucin. All rpoN mutants showed significant reduction of adherence to mucin relative to that of their wild-type parents. In contrast, the adherence of pilin structural gene mutants was similar to the adherence of wild types. These results provide suggestive evidence that P. aeruginosa also binds to mucin via adhesins that are distinct from pilin and are still under the genetic control of rpoN. Unlike the laboratory strain PAK, the clinical strains 1244 and CF613 are capable of agglutinating erythrocytes. The rpoN mutation had a minimal effect on the interaction of bacteria with erythrocytes, indicating that the transcription of a gene(s) specifying the agglutination phenomenon does not utilize rpoN. These findings collectively indicate the existence of several classes of adhesins on the surface of P. aeruginosa that may play an important role in colonization of the human respiratory tract.