The genetic regulation of E. coli K1 capsule biosynthesis and expression has been studied after Gamma, Delta insertion mutagenesis of the plasmid pSR23 which carries the cloned K1 capsule genes. Over 300 mutant strains have been examined and at least seven classes of mutants have been identified. These classes include strains in which K1 capsular polysaccharide expression is (1) abolished, (2) delayed, (3) reduced, (4) enhanced, or (5) temperature sensitive. Growth of Pseudomonads in guinea pig lungs has been studied as a model for a similar infection in the lungs of cystic fibrosis patients. Following intubation of laboratory grown Pseudomonads, we found that: growth in the lung commenced almost immediately; continued for at least 6 hours; 90% of non-growing cells were cleared within 3 hours; and that the clearance rate was reduced, but not abolished, in immune-suppressed guinea pigs.
