Final answer:
The sexually transmitted infection with gum-like lesions called gummas in its tertiary stage is syphilis, caused by the bacterium Treponema pallidum. Syphilis can lead to severe and life-threatening damage especially in its tertiary stage.
Step-by-step explanation:
The sexually transmitted infection characterized by gum-like lesions (gummas) appearing in the tertiary stage is called syphilis. Syphilis is caused by the bacterium Treponema pallidum and can progress through three distinct stages if left untreated: primary, secondary, and tertiary. During tertiary syphilis, which may occur 10 to 20 years after the initial infection, severe symptoms including granulomatous lesions known as gummas can develop on various body parts such as mucous membranes, bones, and internal organs. These lesions can be large, destructive, and potentially fatal, especially when affecting the cardiovascular system as cardiovascular syphilis or the central nervous system as neurosyphilis.