23.2 Bacterial infections of the urinary system  (Page 4/8)

Nongonococcal urethritis (ngu)

There are two main categories of bacterial urethritis: gonorrheal and nongonococcal. Gonorrheal urethritis is caused by Neisseria gonorrhoeae and is associated with gonorrhea, a common STI. This cause of urethritis will be discussed in Bacterial Infections of the Reproductive System . The term nongonococcal urethritis (NGU) refers to inflammation of the urethra that is unrelated to N. gonorrhoeae . In women, NGU is often asymptomatic. In men, NGU is typically a mild disease, but can lead to purulent discharge and dysuria . Because the symptoms are often mild or nonexistent, most infected individuals do not know that they are infected, yet they are carriers of the disease. Asymptomatic patients also have no reason to seek treatment, and although not common, untreated NGU can spread to the reproductive organs, causing pelvic inflammatory disease and salpingitis in women and epididymitis and prostatitis in men. Important bacterial pathogens that cause nongonococcal urethritis include Chlamydia trachomatis , Mycoplasma genitalium , Ureaplasma urealyticum , and Mycoplasma hominis .

C. trachomatis is a difficult-to-stain, gram-negative bacterium with an ovoid shape. An intracellular pathogen, C . trachomatis causes the most frequently reported STI in the United States, chlamydia . Although most persons infected with C. trachomatis are asymptomatic, some patients can present with NGU. C. trachomatis can also cause non-urogenital infections such as the ocular disease trachoma (see Bacterial Infections of the Skin and Eyes ). The life cycle of C. trachomatis is illustrated in [link] .

C. trachomatis has multiple possible virulence factors that are currently being studied to evaluate their roles in causing disease. These include polymorphic outer-membrane autotransporter proteins , stress response proteins , and type III secretion effectors . The type III secretion effectors have been identified in gram-negative pathogens, including C. trachomatis. This virulence factor is an assembly of more than 20 proteins that form what is called an injectisome for the transfer of other effector proteins that target the infected host cells. The outer-membrane autotransporter proteins are also an effective mechanism of delivering virulence factors involved in colonization, disease progression, and immune system evasion.

Other species associated with NGU include Mycoplasma genitalium, Ureaplasma urealyticum , and Mycoplasma hominis . These bacteria are commonly found in the normal microbiota of healthy individuals, who may acquire them during birth or through sexual contact, but they can sometimes cause infections leading to urethritis (in males and females) or vaginitis and cervicitis (in females).