In those with infection dominated by organisms other than P. aeruginosa , erythromycin caused a significant change in microbiota composition ( p = 003 [ by analysis of similarity ] ) , representing a reduced relative abundance of Haemophilus influenzae ( 353 % [ 55-916 ] vs 67 % [ 08-748 ] ; median difference 126 % , 95 % CI 04-283 ; p = 004 ; interaction p = 002 ) and an increased relative abundance of P aeruginosa ( 002 % [ 000-033 ] vs 013 % [ 001-3958 ] ; median difference 66 % , 95 % CI 01-371 ; p = 0002 ; interaction p = 045 ) .