It may be possible to address the issue with discretion and tact during the seminar. You should share your feelings and reaction directly with your colleague, asking for an explanation. If, after this, you still feel the same, discuss the matter with your hierarchy, or that of your colleague if applicable.
[EN] I have just attended a seminar delivered by a colleague and was surprised to see some of my work and results presented without any acknowledgment. What should I do?