Include only three post types in directory shortcode

Shortcode: [gd_cpt_categories]

Parameter: post_type
post_type – The custom post types to use (default = shows all) (examples: ‘gd_place’ or ‘gd_place,gd_event’)

I have four post types and want to show three. What is the syntax, can you give me an example ? I have made a few syntactical tries and can’t get just the three to show.

[gd_cpt_categories post_type=gd_food, gd_product, gd_service]

Thanks