Relationship of K1 antigen to biotype in clinical isolates of Escherichia coli

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Abstract
E. coli isolates, including 105 from blood cultures, 94 from stools of hospital inpatients and 96 from rectal cultures of healthy young adults, were biotyped by the API-20E system and tested for the presence of K1 antigen. The overall frequency of K1 strains was 14.2% and was similar among the 3 sources. Forty-eight biotypes were observed, but 2/3 of all isolates, including 2/3 of the K1 strains, belonged to only 5 biotypes. Among the 5 commonest biotypes, the distribution of K1 strains was nonrandom, since 23 of the 27 K1 strains belonged to only 2 biotypes. Analysis of the O and H antigens of K1 strains indicated that this correlation of biotype with K1 antigen was due to a restricted number of serovars (clones) that were repeatedly isolated from the population studied. These serovars included O18:K1:H7, O1:K1:H6 and O16:K1:H6. Although a statistically significant correlation between biotype and K1 antigen was observed, the correlation was not sufficiently great to allow biotyping to be of significant predictive value as a marker for the K1 antigen.