ORIGINAL ARTICLE Virulence genes in Escherichia coli isolated from calves with diarrhoea in Iran Hadi Pourtaghi & Vahid Dahpahlavan & Hassan Momtaz Received: 7 September 2011 / Accepted: 9 February 2012 / Published online: 8 March 2012 # Springer-Verlag London Limited 2012 Abstract This study was conducted to determine the prev- alence and characteristics of pathogenic Escherichia coli strains from diarrhoeic calves in Iran. A total of 156 E. coli isolates obtained from 180 diarrhoeic calves were evaluated with two multiplex PCR protocols for the detection of the K99, F41, Sta, Stx1, Stx2 and eaeA genes. Of these 156 isolates, 32 (20.5%) carried at least one virulent gene, 22 (14.1%) possessed enterotoxigenic E. coli (ETEC) virulent genes and 10 (6.4%) possessed shiga toxin genes, virulence factors of shiga toxin-producing E. coli (STEC). None of the isolates carried eaeA gene. All ETEC but one were isolated from 1- to 4-day-old calves (95.4%), and one was isolated from a 6-day-old calf. All STEC were isolated from 7- to 28-day-old calves. All ETEC carried both K99 and F41 fimbriae and possessed Sta enterotoxin gene. Keywords Calf diarrhoea . Enterotoxigenic E. coli . Shiga toxin-producing E. coli . Virulence genes . Iran Introduction Neonatal diarrhoea in calves is an important cause of mor- bidity and mortality worldwide (Younis et al. 2009). It is well known that diarrhoea in calves is commonly caused by enterotoxigenic Escherichia coli (ETEC), the most common type of colibacillosis in neonatal calves. ETEC is an impor- tant and global cause of severe watery diarrhoea in the offspring of some animal species such as newborn calves (Nagy and Fekete 2005). Attaching and effacing E. coli (AEEC) and shiga toxin-producing E. coli (STEC) have also been identified as causing diarrhoea in calves (Frank et al. 1998). The main virulence factors of ETEC are fim- briae and enterotoxins. In the first step, mostly F5 and/or F41 fimbriae mediate attachment of the bacteria to the calves' small intestinal microvilli. Then ETEC produce heat-stable enterotoxin class A (Sa), which causes malab- sorption and hypersecretion into the gut lumen (Frank et al. 1998; Nagy and Fekete 1999). Due to the receptor specific- ities of adhesions, ETEC strains seem to be quite host specific. Therefore, animal ETEC strains do not represent a real hazard to humans and cannot be regarded as zoonotic, in contrast to STEC (Nagy and Fekete 2005). The most important virulence factors of STEC are shiga toxins (Stx). Stx1 is immunologically similar to the shiga toxin produced by Shigella dysenteriae, but Stx2 is immunologically differ- ent; STEC isolated from calves produces either Stx1, Stx2 or both (Frank et al. 1998). Stx1 and Stx2 are encoded by Stx1 and Sxt2 genes, respectively (Sepehriseresht et al. 2009). AEEC causes intestinal lesions. The virulence factor of AEEC is intimin protein which is encoded by chromosomal gene eaeA (Frank et al. 1998). A number of diagnostic tests are available for the detection of diarrhoeagenic E. coli; the classical methods are biochem- ical and cell culture assay, ELISA and immunofluorescence H. Pourtaghi (*) : V. Dahpahlavan : H. Momtaz Department of Microbiology, Faculty of Veterinary Medicine, Karaj Branch, Islamic Azad University, Karaj, Iran e-mail: hadi.pourtaghi1@gmail.com H. Pourtaghi : V. Dahpahlavan : H. Momtaz Faculty of Veterinary Medicine, Karaj Branch, Islamic Azad University, Karaj, Iran H. Pourtaghi : V. Dahpahlavan : H. Momtaz Department of Microbiology, Faculty of Veterinary Medicine, Shahrekord Branch, Islamic Azad University, Shahrekord, Iran Comp Clin Pathol (2013) 22:513–515 DOI 10.1007/s00580-012-1442-5