Chancroid
Haemophilus ducreyi is the causative organism of chancroid.
It is a fastidious Gram-negative coccobacillus (very short rod) that requires special media and environmental conditions to grow in culture.
Microscopically, the organism will tend to form long strands forming a pattern described as "railroad tracks" or "a school of fish".
Significantly increases the risk and transmissibility of HIV.
It is exceedingly rare in the US and in developed countries globally.
Chlamydia
Gram-negative obligate, nonmotile intracellular bacteria known as Chlamydia trachomatis.
Typically serotypes D-K.
The most common curable sexually transmitted infection in the United States, according to the CDC and WHO.
Two infectious forms exist, the elementary body (EB) and the reticulate body (RB).
The EB form invades the cell, and the RB form will produce other infectious EB that will infect other non-infectious forms.
Genital Herpes
Genital herpes is caused by the herpes simplex virus 1(HSV-1) or herpes simplex virus 2 (HSV-2).
HSV-1/HSV-2 is a double-stranded DNA virus coated by a lipoglycoprotein with an affinity to infect target cells.
HSV-1 is usually associated with orolabial infections, but according to CDC, HSV-1 is now leading in the cause of genital herpes in young and homosexual patients.
It is estimated that 50 million people in the US are infected with HSV.
Gonorrhea
Gram-negative diplococci bacteria are known as Neisseria gonorrhoeae.
The second most common sexually transmitted infection compared to Chlamydia trachomatis.
Gonorrhea uses glucose to invade mucus epithelial cells.
Gonorrhea modifies cellular proteins that allow further penetration of other organisms.
The proliferation of gonorrhea leads to a localized inflammatory reaction leading to signs and symptoms of a sexually transmitted infection.
Granuloma inguinale
Gram-negative intracellular Klebsiella granulomatis, formerly known as Calymmatobacterium granulomatis.
Rarely found in the United States, it is seen mostly in developing countries, especially in the tropics.
It is most commonly found in the Caribbean, southern Africa, South America, New Guinea, and India.
Human Immunodeficiency Virus (HIV) and Acquired Immunodeficiency Syndrome (AIDS)
Enveloped retrovirus encapsulated with two single-stranded RNA.
Primary HIV signs and symptoms are described as flu-like, often diagnosed as an acute viral syndrome.
The duration of onset of symptoms ranges from 4 to 10 weeks.
Most HIV infections in the US are HIV1.
AIDS is described as the late stage of HIV disease.
The median time to progression from HIV to AIDS is about 11 years but is highly variable.
The risk of syphilis in patients infected with HIV is 77 times greater than in the general population.
Human Papillomavirus (HPV)
HPV is a double-stranded DNA virus that replicates in the basal cell layer of the stratified squamous epithelial cells. This replication cycle induces hyperplasia and possible conversion carcinoma.
HPV types 16 and 18 are oncogenic strains that induce malignant transformation.
HPV types 6 and 11 are common strains that induce anogenital warts, commonly known as condyloma acuminata.
By far, HPV is the most common sexually transmitted infectious organism in the US and worldwide.
Lymphogranuloma venereum
Caused by Chlamydia trachomatis, a Gram-negative obligate, nonmotile intracellular bacteria but a different serotype from the more common chlamydial infections.
Specifically, serotypes or serovars L1, L2, and L3.
Very rare in the US but common in tropical and subtropical regions.
Transmissible through anal, oral, or vaginal sexual contact.
Most frequently found in men who have sex with other men.
Closely associated with HIV infections.
Mycoplasma genitalium
Mycoplasma genitalium is the second most common cause of nongonococcal urethritis after chlamydia and a common cause of female cervicitis.
It is a common cause of resistant or recurrent urethritis.
Mycoplasma is very slow growing in a culture which can take up to 6 months.
Since it lacks a cell wall, it can't be Gram stained.
Risk factors include young age (<25 years), smoking, frequent sexual contacts, and a larger number of sexual partners.
Closely associated with HIV infections.
Syphilis
Caused by a tiny spirochete bacterium, Treponema pallidum.
T. pallidum is very slow growing and cannot be cultured nor seen on standard light microscopy.
The initial immune response is muted because T. pallidum has few exposed proteins and its outer membrane lacks lipopolysaccharides.
Syphilis infections are increasing compared to previous reports, according to the CDC.
Syphilis is far more common in the developing world, particularly among the poorest populations with the most limited access to healthcare.
Syphilis presents with a painless chancre, which is a well-demarcated lesion at the site of inoculation.
Syphilis presents in various forms, depending on the duration known as Primary, Secondary, or Tertiary.
It affects about 12% of all gay men (men having sex with men) globally.
Trichomoniasis
Caused by single-celled flagellated anaerobic protozoa known as Trichomonas vaginalis.
Trichomoniasis causes direct damage to the epithelium. The injuries lead to microulcerations primarily in the vagina, cervix, urethra, and paraurethral glands.
Garcia, M.R., Leslie, S.W., & Wray, A.A. (2022). Sexually Transmitted Infections. National Library of Medicine. https://www.ncbi.nlm.nih.gov/books/NBK560808/ .