Neisseria gonorrhoeae is a classic sexually transmitted bacterium that is transmitted by close contact. Its frequency has been rising sharply over the last decade. It causes inflammation of the mucous membranes of the urinary tract, genitals, throat, buttocks and conjunctiva. In most cases, the infection is asymptomatic. Untreated infection leads to complications such as inflammation of the prostate and perineum in men and pelvic inflammatory disease and infertility in women. It can also cause acute inflammation of the joints and heart valves.

Chlamidia trachomatis is an intracellular bacterium and causes the most common sexually transmitted infection in the developed world. Especially in young people who also have frequent recurrent infections. The most common infection is asymptomatic, but can cause many complications, most notably pelvic inflammatory disease, ectopic pregnancy, and infertility. Transmission to the baby during childbirth can cause blindness.

Trichomonas vaginalis is the protozoan that causes the most common sexually transmitted infection trichomoniasis. Worldwide, it is even more common than chlamydia and gonorrhea. The disease can be successfully identified using modern diagnostic methods, and treatment is very effective. Infection in most cases is asymptomatic, but can occur up to 28 days after infection. It infects the vagina and urethra in women and only the urethra in men. When the infection occurs, it is easily transmitted through genital contact.

Mycoplasma genitalium was only discovered in the 1980s and is becoming an increasingly important cause of many sexually transmitted infections. Symptoms may or may not be specific, and untreated infection can lead to severe complications. It is the most common cause of inflammation of the urethra in men and causes inflammation of the vagina in women. It is thought that men may have difficulty fertilizing a woman due to MG infection.