O-SEROGROUP, BIOTYPES, AND EAE GENES IN ESCHERICHIA-COLI STRAINS ISOLATED FROM DIARRHEIC AND HEALTHY RABBITS

A total of 305 Escherichia coli strains isolated from diarrheic and he althy rabbits in 102 industrial fattening farms from different areas o f Spain were serotyped, biotyped, and tested for the presence of the e ne gene and toxin production. The characteristics found in strains iso lated from healthy rabbits were generally different from those observe d in E. coli strains associated with disease. Thus, strains with the e ae gene (74% versus 22%); strains belonging to serogroups O26, O49, O9 2, O103, and O128 (64% versus 12%); rhamnose-negative strains (51% ver sus 5%); and rhamnose-negative O103 strains with the eae gene present (41% versus 1%) were significantly (P < 0.001 in all cases) more frequ ently detected in isolates from diarrheic animals than in those from h ealthy rabbits. Whereas a total of 35 serogroups and 17 biotypes were distinguished, the majority of the strains obtained from diarrheic rab bits belonged to only four serobiotypes, which in order of frequency w ere O103:B14 (72 strains), O103:B6 (16 strains), O26:B13 (12 strains), and O128:B30 (12 strains). These four serobiotypes accounted for 48% (112 of 231) and 5% (4 of 74) of the E. coli strains isolated from dia rrheic and healthy rabbits, respectively. Only six strains were toxige nic (three CNF1(+), two CNF2(+), and one VT1(+)). We conclude that ent eropathogenic E. E. coli strains that possess the eae gene are a commo n cause of diarrhea in Spanish rabbit farms and that the rhamnose-nega tive highly pathogenic strains of serotype O103:K-:H2 and biotype B14 are especially predominant. Detection of the eae gene is a useful meth od for the identification of enteropathogenic E. coli strains from rab bits. However, a combination of serogrouping and biotyping may be suff icient to accurately identify the highly pathogenic strains for rabbit s.