Abstract
Limited information is available on shiga toxin producing Escherichia coli (STEC) in pigs and infants from Aizawl, Mizoram and North Eastern region of India. This cross sectional study was conducted on faecal samples from pigs and infants to detect and characterize of STEC and enteropathogenic E. coli (EPEC). Serogrouping, molecular and phenotypic characterizations were done by standard molecular and cytotoxic assays. Out of 48 E. coli strains isolated from 320 diarrhoeic fecal samples of piglets, 44 belonged to 18 different serogroups, 3 (6.25%) were untypeable (UT) and 1(2.08%) was recorded as rough strain (R). Similarly, out of 17 E. coli strains isolated from 264 diarrhoeic fecal samples of infants, 16 belonged to O60 (94.1%) and 1(5.88%) was untypeable. Virulence genes (stx1, stx2, eaeA and hlyA) were detected by multiplex PCR assay. A total of 1260 E. coli were isolated from piglets (720) and infants (540) from 584 faecal samples. All together, 5.16% (65) E. coli isolates were found to be positive for at least one virulence gene (6.66% piglets and 3.15% infants). Out of the virulent gene positive E. coli 3.17% (32 from piglets and eight from infants) and 1.98% (16 from piglets and nine from infants) were recorded as STEC and EPEC, respectively. On the other hand, from the total 2.14% stx2 positive isolates, 16 and 11 were positive for stx2e and stx2c subtypes, respectively. Similarly, from the 4.04% eaeA positive isolates, 1.19% (15) were positive for bfpA gene, of which 1.67% (12) were piglets and 0.60% (3) were infants. All the isolates were exhibited varying degree of CPE on vero cell lines. In conclusion, STEC and EPEC seem to be associated with diarrhoea in piglets and infants in Mizoram. In piglets STEC strains represent as a major cause of diarrhoea while EPEC strains represent as major cause of diarrhoea in infants in North Eastern region of the India. Key words: Enteropathogenic E. coli (EPEC), infants; piglets, shigatoxigenic E. coli (STEC), vero cell cytotoxicity.  
Highlights
Pathogenic Escherichia coli are one of the most important groups of bacteria causing diarrhoea and extraintestinal infections in human and animals (Levine, 1987)
Out of 48 E. coli strains isolated from 320 diarrhoeic fecal samples of piglets, 44 belonged to 18 different serogroups, 3 (6.25%) were untypeable (UT) and 1(2.08%)
Out of 17 E. coli strains isolated from 264 diarrhoeic fecal samples of infants, 16 belonged to O60 (94.1%) and 1(5.88%) was untypeable (Table 3)
Summary
Pathogenic Escherichia coli are one of the most important groups of bacteria causing diarrhoea and extraintestinal infections in human and animals (Levine, 1987). Major diseases caused by E. coli are piglet diarrhoea (Fair brother et al, 2000), oedema disease (Chen et al, 2004) and postweaning diarrhoea in pigs (Choi et al, 2001) In human, it causes infant diarrhoea, thrombotic thrombocytopenia purpurea (Paton and Paton, 2005), haemorrhagic colitis (HC) and haemolytic uraemic syndrome (HUS) (Nataro and Kaper, 1998; Leelaporn et al, 2003; Paton and Paton, 2005; Zweifel et al, 2006). Shigatoxin producing E. coli (STEC), known as verotoxin producing E. coli (VTEC), comprises a serologically diverse group of pathogens that cause disease in humans and animals (Barman et al, 2008). Two major groups of Stxs are named as stx and stx; where the former one is nearly identical to the toxin of Shigella dysenteriae type 1. stx shares less than 60% amino acid sequence with stx (Barman et al, 2008)
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