Variants of astA gene among extra-intestinal Escherichia coli of human and avian origin

Many Escherichia coli strains harbour astA , which is the gene encoding the enteroaggregative E. coli heat-stable enterotoxin (EAST1). This gene is embedded in a putative transposase (ORF1) and presents polymorphism in diarrheagenic strains. Although astA and orf1 are detected in extra-intestinal strains, little is known about polymorphism and differential gene transcription in this pathotype. In the present work, extra-intestinal E. coli from humans (ExPEC) and poultry (APEC) were assayed to verify the presence of astA/orf1 and possible polymorphisms in these genes. Three astA/orf1 patterns were detected via Sanger sequencing. Pattern 1 was novel and represented an astA pseudogene. Pattern 2 and pattern 3 presented distinct amino acids within the reading frame encoding ast A and were identical to the sequences found in EAEC 17-2 and EAEC 042, respectively. Regarding the frame encoding ORF1, all mutations detected in the three patterns were neutral. The transcripts of astA / orf1 in vitro were underregulated in strains possessing the pattern 1 sequence. The results demonstrate that the same astA sequences may be detected in diarrheagenic and extra-intestinal E. coli . However, extra-intestinal isolates may also present an astA pseudogene that has not been reported in diarrheagenic E. coli .