ESCHERICHIA-COLI IN BACTEREMIA - O-ACETYLATED K1 STRAINS APPEAR TO BE MORE VIRULENT THAN NON-O-ACETYLATED K1 STRAINS

A total of 174 blood isolates of Escherichia coli, collected during a 5-year period at the University Hospital Utrecht, were serotyped with rabbit sera against 171 0 antigens and 73 capsule (K) antigens. The four most prevalent O-antigen serotypes were 06 (n = 22), 018 (n = 19), 01 (n = 19), and 02 (n = 15). Thirty-one strains were not typeable with any of the 0-antigen-typing sera. Of the 148 strains that were subjected to K-antigen serotyping, 34 strains lacked a K antigen and 41 were not typeable with the K-antigen-specific antisera used in the study. Kl was by far the most frequently found K-antigen serotype; this was followed by K2, K53, K5, K13, K7, K(A)28, and K15. Strains possessing a K1 antigen were further classified as either 0-acetyl-positive (n = 12) or O-acetyl-negative (n = 21) strains. Retrospective analysis of patients infected with different E. coli isolates-nonencapsulated (n = 23), 0-acetylated K1 (n = 12), and non-0-acetylated Kl (n = 21)-revealed clinical differences. More patients suffered from sepsis (94% versus 74%), and a higher rate of mortality was found in the group infected with K1 isolates (18 versus 9%) than in the group infected with nonencapsulated isolates. More patients with severe sepsis (25 versus 10%) and a higher mortality (33 versus 10%) were found in the group infected with 0-acetylated K1 isolates than in the group infected with non-0-acetylated isolates. Also, the hospitalization of these patients was prolonged. Thus, O-acetylated E. coli K1 strains seem to be more virulent than non-O-acetylated K1 strains.