Strains used in this study and their characteristics.

1Patient: confirmed case of diarrhea; human: unknown diarrhea status. 2Villages coded with letters A to F from which strains were isolated. 3PT, pulse type; ST, sequence type. 4O157 antigen determined by agglutination with O157 antiserum. 5*: adhesion index of <1; **: 1< adhesion index of <50; ***: adhesion index of >50. 6LDH (%±SD): the lactate dehydrogenase released from HEp-2 cells. 7Tellurite resistance: Numbers are the tellurite concentration in µg/ml. -: no growth with tellurite concentration at 2 µg/ml, the lowest tested. 8Five genes from the T6SS were tested (CF74_0731, CF74_0734, CF74_0737, CF74_0743, and CF74_0745). CF_0734 and CF_0745 were not detected in the strains with 3 genes present.