Detection and characterization of Shiga toxin-producing Escherichia coli in feral pigeons

Escherichia coli strains producing a variant of Shiga toxin 2 (Stx2), desig nated Stx2f, have been recently described in the stools of feral pigeons. D uring 1997-1998, 649 pigeons were trapped and examined in three different s quares of Rome. Stool samples were collected from each bird and enrichment cultures were examined for the presence of Stx by the veto cell assay. Stx- producing E. coli (STEC) were isolated from the positive cultures and chara cterized by serotyping and PCR analysis of stx and other virulence-related genes. Stx was detected in 10.8% of the stool enrichment cultures. The perc entage of positive birds did not differ significantly for the three flocks considered and the season of sample collection. Conversely. STEC carriage w as significantly more frequent in young than in adult birds (17.9 versus 8. 2%). None of the birds examined showed signs of disease. STEC strains were isolated from 30 of 42 Stx-positive cultures examined. All the strains prod uced Stx2f, and most of them possessed genes encoding for intimin and the c ytolethal distending toxin (CLDT). Six serogroups were identified. but most of the isolates belonged to 045, 018ab, and 075. Molecular typing indicate d that most of the isolates within a flock were clonally-related. This work confirms that pigeons represent a natural reservoir of STEC strains charac terized by the production of the toxin variant Stx2f, and by the frequent p resence of eae and cldt genes. Further work is needed to clarify whether th ese STEC may represent a cause of avian disease or even a potential health hazard for humans. (C) 2001 Elsevier Science B.V. All rights reserved.