Virulence factors of avian Escherichia coli associated with swollen head syndrome.

Virulence characteristics of 50 strains of Escherichia coli isolated from chickens with swollen head syndrome were examined. The results were the following: in the absence of D-mannose, 74% of strains agglutinated guinea pig erythrocytes, but in the presence of D-mannose 32% agglutinated guinea-pig erythrocytes and 62% agglutinated human erythrocytes. When slide agglutination assays were carried out with antisera to adhesin of bovine and swine origin (K88, K99, F41, F42 987P and 2134P), only 14% of strains agglutinated with antiserum to F41. Colicin V was produced by 78% of the E. coli strains and 80% produced aerobactin. In the serum resistance test, 36 (72%) of strains showed resistance to normal chicken serum. Only seven (14%) strains expressed K1 capsular antigen, while motility was found in 62% of the strains.