The afa-related gene cluster in necrotoxigenic and other Escherichia coli from animals belongs to the afa-8 variant.
Six hundred and nine necrotoxigenic Escherichia coli type 1 and 2 (NTEC1 and NTEC2) and non-NTEC isolated in Western and Southern Europe, North Africa and Canada from diseased calves, pigs, humans, poultry, and 55 isolated from asymptomatic calves were studied for the identification of afa-related sequences to the recently described afa-7 and afa-8 gene cluster variants from two bovine Escherichia coli (Lalioui et al., 1999). Colony hybridization and PCR assays for the afaD-7, afaE-7, afaD-8 and afaE-8 identified the afa-related sequences to the afa-8 gene cluster in most (67/79; 85%) of the E. coli positive with the Afa-f family probe and in 14 additional strains negative with the Afa-f probe. No E. coli was positive for the afa-7 gene cluster. The existence of afa-8 positive strains was thus confirmed among bovine E. coli and for the first time among porcine, poultry and human E. coli. Sequencing of the afaE-8 amplicon of nine strains from the different host species showed a high degree of conservation (>95% at the DNA level; >92% at the amino-acid level). The afa-8 gene cluster was more frequent in E. coli from diseased calves (18%) than from piglets (12%), humans (6%) and poultry (5%). Bovine NTEC2 (26%) were more frequently positive than NTEC 1 (20%) and non-NTEC (11%). E. coli isolated from asymptomatic calves were rarely positive: one NTEC2 (3%) and no non-NTEC. The afa-8 gene cluster was located on the Vir plasmid in 11/23 NTEC2, but no plasmid localization was detected in NTEC1 or non-NTEC.
Gérardin
J
J
Chaire de Bactériologie et de Pathogénie Bactérienne, Faculté de Médecine Vétérinaire, Université de Liège, Sart-Tilman, B-4000, Liège, Belgium.
Lalioui
L
L
Jacquemin
E
E
Le Bouguénec
C
C
Mainil
J G
JG
D018830:Adhesins, Escherichia coli / Q000235:genetics*; D000818:Animals; D002417:Cattle; D002645:Chickens; D004269:DNA, Bacterial / Q000737:chemistry; D004926:Escherichia coli / Q000235:genetics*; D004927:Escherichia coli Infections / Q000235:genetics / Q000662:veterinary*; D006388:Hemagglutinins / Q000235:genetics*; D006801:Humans; D009693:Nucleic Acid Hybridization; D010957:Plasmids; D016133:Polymerase Chain Reaction / Q000662:veterinary; D013552:Swine
D018830:Adhesins, Escherichia coli; D004269:DNA, Bacterial; D006388:Hemagglutinins