Multiple of isolates of Pseudomonas aeruginosa with differing antimicrobial susceptibility patterns from patients with cystic fibrosis.

Clinical isolates of Pseudomonas aeruginosa from patients with cystic fibrosis were studied 
in an effort to determine the unique characteristics of the infecting 
strains and to elucidate the pattern of colonization. Of 413 patients 
studied, 81% were chronically infected with P. aeruginosa. Patients from whom 
P. aeruginosa was never or only occasionally isolated were in better 
clinical condition than the chronically infected patients. Isolates were classified into 
six morphologic varieties: classic, rough, mucoid, gelatinous, dwarf, and enterobacter. Most 
patients had two or more of these varieties. Such multiple varieties 
from the same individual were of the same serotype but often 
differed in antibiotic susceptibility as determined by both the disk and 
the minimal inhibitory concentration methods. These differences were apparent when mucoid 
strains were compared with nonmucoid strains and when nonmucoid strains were 
compared with one another. Studies of antibiotic susceptibility should be performed 
on each morphologically different type of P. aeruginosa obtained from patients 
with cystic fibrosis. 