The role of pili and capsule was studied in neonatal infection with Escherichia coli K1. E coli strains were selectively cultured into three phases: mannose-sensitive (MS) piliated, non-mannose-sensitive (NMS) piliated, and nonpiliated. A high percentage of neonatal rats fed each phase of K1 strains developed bacteremia; there was no bacteremia with non-K1 strains or an acapsular mutant of K1 strain C94 (C94K-). Oral cavity colonization was noted in nearly 100% of rats fed K1 strains, non-K1 strains, or C94K-, regardless of the phase of piliation at feeding. Only MS piliated bacteria were found on oral cavity culture, indicating a rapid shift of NMS piliated and nonpiliated bacteria to the MS piliated phase. Conversely, only nonpiliated bacteria were found on blood culture when neonatal rats were fed piliated bacteria. Colonization of ileal epithelium was not observed. Thus, in vivo phase variation may be important in colonization and bacteremia with E coli K1.
We examined the effect of host age and health status on the adherence of mannose-sensitive piliated Escherichia coli Kl to human oral epithelial cells. Mannose-sensitive piliated bacteria adhered in comparable numbers to newborn, older infant, and adult cells (125 61, 198 54, and 139 ± 69 bacteria per cell, respectively). Prematurity and serious illness did not alter adherence in newborns. The increased susceptibility of premature newborns to E. coli Kl cannot be explained by enhanced epithelial cell adherence.
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