INFLUENCE OF SOME BACTERIAL AND HOST FACTORS ON COLONIZATION AND INVASIVENESS OF ESCHERICHIA-COLI K1 IN NEONATAL RATS

Of 209 healthy infants examined, 44 (21.1%) carried Escherichia coli K 1 in their feces. Of these 44 isolates, 36 (81.8%) were attributed to 10 different known clonal groups of E. coli K1 and 4 isolates represen ted unknown types. The influence of mannose-resistant (MR) adhesins, a erobactin production, and resistance to serum on colonization and inva siveness of E. coli K1 in orally infected inbred LEW baby rats was inv estigated. Strains expressing MR adhesins had significantly higher col onization and invasion rates than non-MR strains did. Mixed-infection experiments of LEW rats revealed interactions between different types of E. coli Kl strains affecting colonization and invasion rates. P-fim briated strains appeared to have a selective advantage for colonizatio n. The bacteremic potentials of different E. coli Kl strains could not be associated with their resistance to sera from LEW rats free of mem bers of the family Enterobacteriaceae. No differences in virulence bet ween fecal E. coli Kl isolates and clinical isolates from diseased hum ans were found. An influence of the major histocompatibility complex o n host susceptibility to invasive E. coli K1 was indicated by comparin g the parental LEW rat strain with different congenic LEW strains (RT1 ).