Epidemiological markers for Pseudomonas aeruginosa. 6. Relationship between concomitant non-mucoid and mucoid strains from the respiratory tract in cystic fibrosis.

The simultaneously occurring mucoid (M) and non-mucoid (NM) variants of Pseudomonas aeruginosa 
frequently observed in cultures from the respiratory tract of chronically infected 
cystic fibrosis patients have been studied. M cultures in vitro were 
unstable and easily dissociated NM colonies. In a large proportion of 
the cases, M and NM variants occurring simultaneously in cultures from 
one and the same clinical specimen were of the same pyocine 
type, phage type, and serogroup. In some remaining cases there were 
small differences between the M and NM variants such that identity 
between the variants from one and the same specimen was possible, 
although not definite. The NM dissociants from M strains were of 
the same type as the M variant. The possible role of 
cross-infection and the interaction of bacteria and host response factors continuously 
tending to select the unstable M variant in vivo are discussed. 
