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Phagocytic resistance of Escherichia coli K-1 isolates and relationship to virulence
Abstract:
Blood culture isolates from 133 episodes of Escherichia coli bacteremia were typed for K-1 capsular antigen by immunodiffusion, utilizing equine antiserum raised against meningococcal group B polysaccharide. Twenty-six percent (34 of 133) of these isolates were positive for K-1 antigen. These 133 strains, 34 K-1 and 99 non-K-1, were tested for susceptibility to phagocytosis. K-1 strains were found to be more resistant to clearance (27%) than non-K-1 strains (71%) when tested in an in vitro opsonophagocytic/killing assay containing normal human granulocytes and plasma. Additional studies demonstrated that resistance was due to decreased phagocytosis rather than diminished intraleukocytic killing. K-1 strains obtained from stool showed a similar degree of resistance to phagocytosis when compared with K-1 blood isolates. A comparison of clinical data on non-neonatal patients with E. coli K-1 and non-K-1 bacteremia showed no significant differences in mortality for these two groups. The incidence of shock for patients bacteremic with K-1 strains (74%) was significantly greater than that for patients bacteremic with non-K-1 strains (33%). These differences are attributed to the increased resistance to phagocytosis observed for K-1 versus non-K-1 E. coli isolates.
Insights
Escherichia coli K-1 antigen enhances bacterial resistance to phagocytosis, increasing the risk of shock in bacteremia patients. Non-K-1 strains are cleared more effectively by immune cells.
Area of Science:
- Microbiology
- Immunology
- Infectious Diseases
Background:
- Escherichia coli (E. coli) is a common cause of bacteremia.
- The K-1 capsular antigen is a virulence factor found in some E. coli strains.
- Understanding the interaction between E. coli K-1 and the host immune system is crucial for managing bacteremia.
Purpose of the Study:
- To investigate the role of the K-1 capsular antigen in E. coli resistance to phagocytosis.
- To compare the clinical outcomes of bacteremia caused by K-1 positive and K-1 negative E. coli strains.
Main Methods:
- Blood culture isolates of E. coli were typed for the K-1 antigen using immunodiffusion.
- Susceptibility to phagocytosis was assessed using an in vitro opsonophagocytic/killing assay with human granulocytes and plasma.
- Clinical data from patients with E. coli bacteremia were analyzed and compared between K-1 positive and negative groups.
Main Results:
- Twenty-six percent of E. coli bacteremia isolates were positive for the K-1 antigen.
- K-1 positive E. coli strains exhibited significantly greater resistance to phagocytosis and clearance by human immune cells compared to non-K-1 strains.
- While mortality rates were similar, patients with K-1 E. coli bacteremia had a higher incidence of shock (74%) than those with non-K-1 strains (33%).
Conclusions:
- The K-1 capsular antigen contributes to E. coli's resistance to phagocytosis, a key factor in its virulence.
- Increased resistance to phagocytosis by K-1 E. coli is associated with a higher risk of shock in bacteremia, not necessarily increased mortality.
- These findings highlight the importance of the K-1 antigen in E. coli pathogenesis and suggest potential targets for therapeutic strategies.