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.