Serotyping of Pseudomonas aeruginosa isolates from patients with cystic fibrosis of the pancreas.

Pseudomonas aeruginosa isolates (173) from 144 patients with cystic fibrosis (CF) of 
the pancreas in seven hospitals were serotyped with the agglutination systems 
of Homma (1974) and Fisher et al. (1969). The two systems 
were complementary. Strains from CF patients were much less likely to 
furnish a stable type on repetitive typing tests than strains from 
other patients. This was related to the frequent occurrence of mucoid 
P. aeruginosa strains. The 173 strains were divided among 11 Homma 
serotypes. A single Homma type (type 8) capable of mucoid growth 
comprised 104 (60%) CF strains. Eight serotypes were detected in 77 
strains from 48 CF patients in one hospital; three strains were 
detected in one hospital CF unit; and two strains were detected 
in each of five hospital CF units. The CF serotype comprised 
from 50 to 93% of CF strains in the seven hospitals. 
These P. aeruginosa strains dissociated in vivo as judged by mucoid 
and nonmucoid colonies on primary culture plates and continued to dissociate 
during subcultures. Both colony type were the same serotype. The tendency 
to regard colonial phenotypes (mucoid, nonmucoid, rough) as separate strains was 
erroneous. Repetitive typing with the two systems gave better results than 
a single system. The mucoid P. aeruginosa strain is probably spread 
from patient to patient, rather than acquiring its mucoid characteristic de 
novo in the CF patient. It is not known why the 
mucoid CF strain has a peculiar predilection for CF patients, nor 
why it generally loses the quality in culture but retains it 
indefinitely in the patient. 