Adhesion of pilA and fliD mutants of P. aeruginosa PAK to mucin. PAK-NP, pilA mutant of PAK; PAK-NPD, pilA fliD mutant of PAK; PAK-NPD (375D), PAK-NPD complemented with the complete fliD gene on a multicopy plasmid vector, pPZ375; PAK-NPD (375), PAK-NPD with the vector pPZ375. Differences shown by asterisks are significant (∗ versus ∗∗, P < 0.001) by Student’s t test.