Traveller’s diarrhoea is most commonly caused by
Five types of E.coli include:
1. ETEC (enterotoxogenic E.coli)
2. EIEC (enteroinvasive E.coli)
3. EPEC (enteropathogenic E.coli)
4. EHEC (enterohemorrhagic E.coli)
5. EAEC (enteroaggregative E.coli) 
Traveller's diarrhoea is most commonly caused by enterotoxogenic E.coli and then the other common organism responsible is S. dysenteriae. Intestinal Pathogenic E. Coli.
ETEC
S. dysenteriae
EPEC
Salmonella