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David Taylor-Robinson

and Jørgen Skov Jensen


May 30, 2013: This chapter has been re-evaluated and remains up-to-date. No changes have been necessary.


Chapter reviewed and minor alternations made.

Updated on 31 May 2012. The previous version of this content can be found here.
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date: 29 April 2017

Mycoplasmas are the smallest self-replicating prokaryotes. They are devoid of cell walls, with the plasticity of their outer membrane favouring pleomorphism, although some have a characteristic bottle-shaped appearance. Mycoplasmas recovered from humans belong to the genera Mycoplasma (14 species) and Ureaplasma (2 species). They are predominantly found in the respiratory and genital tracts, but sometimes invade the bloodstream and thus gain access to joints and other organs.

Respiratory infection

Clinical features—Mycoplasma pneumoniae is the most important mycoplasmal respiratory pathogen, with presentations ranging from inapparent infection and mild, afebrile, upper respiratory-tract disease to severe pneumonia. It is responsible for 15 to 20% of all pneumonias in the United States of America, and is particularly common in older children and younger adults. Extrapulmonary manifestations include Stevens–Johnson syndrome and haemolytic anaemia.

Diagnosis and treatment—diagnosis is made by culture (slow and of limited value in clinical diagnosis), molecular methods (rapid detection by PCR is routine in some settings) and/or serology. Aside from supportive care, treatment is usually with tetracyclines or erythromycin. There is no commercially available effective vaccine.

Genitourinary and related infections

Clinical features—(1) Men—M. genitalium causes nongonococcal urethritis (NGU) in men, and ureaplasmas may play a role in some cases. (2) Women—M. genitalium causes urethritis, cervicitis, endometritis, and possibly salpingitis; M. hominis and (to a lesser extent) ureaplasmas are associated with bacterial vaginosis; M. hominis may contribute to salpingitis. (3) Pregnancy—ureaplasma infection of amniotic fluid is associated with preterm labour; ureaplasmas may be involved in the chronic lung disease of very low birthweight babies.

Diagnosis and treatment—diagnosis of infection by ureaplasmas and M. hominis is usually by culture of swabs from the urethra or cervix/vagina; PCR is used to detect M. genitalium. Patients with NGU should receive an antibiotic with activity against C. trachomatis, ureaplasmas, and M. genitalium, e.g azithromycin, with moxifloxacin used if M. genitalium becomes resistant and chronic disease develops.

Rheumatological manifestations

(1) Chronic arthritides—M. fermentans has been detected in the joints of patients with, e.g. rheumatoid arthritis, but the significance of this is unknown. (2) Reiter’s syndrome—sexually acquired reactive arthritis (SARA) is not uncommon after M. genitalium-positive NGU, but no causal link has been established. (3) Arthritis in patients with hypogammaglobulinaemia is often caused by mycoplasmas (particularly ureaplasmas).

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