Shiga toxin-producing Escherichia coli strains produce at one or both of the two types of Shiga toxins (Stx1, Stx2). In humans, these pathogens cause diarrhea, hemorrhagic colitis and HUS, the leading cause of acute renal failure in children .
The natural reservoirs of STEC are ruminants, particularly cattle. Although some authors [2, 3] have reported that E. coli isolated from chickens may harbor Shiga toxin-encoding genes, there is still no consensus on whether these animals can be considered as reservoirs of STEC strains.
We genotypically and phenotypically analyzed 110 E. coli isolated in São Paulo, Brazil from chickens with cellulitis (60 isolates) and SHS lesions (50 isolates) to confirm the presence of STEC. These isolates harbored genes considered as minimal predictors of virulence for APEC .
Thirty-four of these APEC strains [30.90%] harbored the stx genes according to conventional PCR as described by Paton and Paton . Eighteen of these [52.94%] were isolated from chickens with cellulitis and 16 [47.06%] from chickens with SHS lesions. The most frequent stx genotype was stx1+/stx2+ (61.76%) followed by stx1+/stx2− (38.24%).
Cell-free filtrates of the 34 APEC stx+ exhibited cytotoxic activity similar to culture supernatants of E. coli O157:H7 EDL933 in Vero (African green monkey kidney) and human umbilical vein endothelial cells.
It is estimated that STEC O157 causes about 36% of infections and non-O157 STEC cause the rest . In our study, none of the 34 STEC belonged to the O157:H7 serotype.
Moreover, only one of the strains harbored the eae gene encoded in the LEE. Although many authors have reported that the LEE locus is essential for host colonization and virulence of A/E pathogens , others state that, because a significant number of cases of severe disease, including HUS in humans, as well as sporadic outbreaks, are caused by STEC LEE−  and these sporadic and outbreak cases of severe disease are indistinguishable from those caused by STEC O157:H7 LEE+ , the presence of the LEE locus is not essential for pathogenesis.
These genotypic and phenotypic data suggest that chickens act as reservoirs of STEC. We here suggest that the nomenclature for AP-STEC (avian pathogenic Shiga toxin-producing E. coli) should be discussed.
Our data suggest that, in addition to cattle and goats, broiler chickens are also important reservoirs for STEC, increasing the risk of transmission of these pathogens to human hosts.
Robert Alvin Bernedo-Navarro,
Mayara Mayele Miyachiro,
Rogério Arcuri Conceição,
Department of Genetics, Evolution and Bioagents, Institute of Biology, State University of Campinas (UNICAMP), Rua Monteiro Lobato 255, Campinas, SP CEP 13083-826, Brazil