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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 extraintestinal strains, little is known about polymorphism and differential gene transcription in this pathotype. In the present work, extraintestinal E. coli from humans (ExPEC - Extraintestinal Pathogenic E. coli) and poultry (APEC - Avian Pathogenic E. coli) 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 astA 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, extraintestinal isolates may also present an astA pseudogene that has not been reported in diarrheagenic E. coli., (© FEMS 2016. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

In a prospective study between February 2003 and June 2004, stool specimens of children less than 2 years of age with diarrhoea (n=218) and without diarrhoea (n=86), living in Vitória, Espírito Santo, Brazil, were examined for the presence of diarrhoeagenic Escherichia coli. E. coli isolates were tested by colony blot hybridization with specific DNA probes designed to detect EPEC, ETEC, EIEC, EAEC, DAEC and EHEC/STEC. Diarrhoeagenic E. coli strains were detected as the sole pathogen in stools of 92 (30.3 %) children, including 72 (33.0 %) with diarrhoea and 20 (23.2 %) without diarrhoea. DAEC was the most frequent pathotype and was found significantly more often from patients (18.3 %) than from controls (8.1 %) (P<0.05), particularly among children more than 1 year of age (P=0.01). Atypical EPEC and EAEC isolates were isolated from both patients (5.5 % and 4.6 %, respectively) and controls (6.9 % and 6.9 %, respectively). ETEC was more frequently isolated from patients (3.2 %) than controls (1.2 %). Typical EPEC (0.9 %) and EIEC (0.4 %) isolates were detected only in children with diarrhoea. In conclusion, our data suggest that DAEC should be considered potential pathogens in the region of Brazil studied.

Virulence properties of 31 atypical enteropathogenic Escherichia coli (EPEC) strains isolated from cases of diarrhoea were examined. All except two strains adhered to HEp-2 cells in a localised adherence-like (LAL) pattern. With the exception of two strains, all were fluorescent actin staining (FAS) positive. Gentamicin HEp-2 invasion assay studies showed that all strains were invasive. Transmission electron microscopy of infected HEp-2 cells showed the characteristic attaching and effacing lesion and invasion of the cultured cells. Of the nine strains that hybridised with a DNA probe for alpha-haemolysin, five were haemolytic within 3 h of incubation, while the remaining strains were haemolytic only after incubation for 24 h. Three strains produced enterohaemolysin on blood agar. None of the 31 strains of E. coli induced fluid accumulation in the rabbit intestinal loop assay or displayed cytotoxic effects in HeLa and Vero cells. All the strains belonging to serotypes O26:H11, O26:H- and 0119:H2 expressed intimin beta, whereas all the strains from serotype O55:H7 expressed intimin gamma. The strains belonging to serogroup O111 expressed a non-typable intimin. The participation of intimin in LAL was supported by adhesion inhibition experiments in which antibodies to intimin significantly reduced the level of LAL.