HPS4-YC infection in STEC. A Giemsa staining of HPS4-YC infecting STEC (100×). STEC were uninfected or infected with HPS4-YC at an MOI of 10, 100 or 1000 for 2 h. The black arrows point to the bacteria present. Scale bar, 20 μm. B, C Adherence and invasion assays. STEC were infected with HPS4-YC at different MOI for 2 h. The number of adherent and invasive bacteria per well was counted. D Cell viability of STEC were assessed by CCK-8. The results represent the means ± SD of three independent experiments. Significant differences in B and C were analyzed using Student t test. Significant differences in D were analyzed using one-way ANOVA. ns: not significant; ***P < 0.001.