Mycoplasma are tiny bacteria that lack a cell wall. Their outer cell membrane contains sterols that they obtain from the tissues in which they grow. Mycoplasma pneumoniae is second only to the pneumococcus as a cause of community-acquired pneumonia. However, M pneumoniae has a predilection for younger persons and spreads person-to-person in families or closed groups, whereas the elderly are at greatest risk for pneumococcal pneumonia. Mycoplasmal infection presents as tracheobronchitis or pneumonia with headache and a persistent nonproductive cough, often worse at night. Chest radiographs usually show unilateral patchy infiltrates without lobar consolidation, hence the term atypical pneumonia. The course is almost always benign, but improvement is accelerated by treatment with doxycycline or azithromycin. In the past, diagnosis was confirmed if at all by serology or rarely by culture. Multiplex PCR platforms for respiratory pathogens and pneumonia have changed the approach to diagnosis.
There has been a resurgence interest and research in Mycoplasma genitalium (MG ), which is second only to Chlamydia trachomatis as a cause of cervicitis, urethritis, and pelvic inflammatory disease (PID). The recognition of MG as a major cause of sexually transmitted infection (STI) has been transformed by NAA testing, since it does not grow in culture. Gene variations that result in resistance to macrolides and fluoroquinolones are an emerging problem globally.
Mycoplasma hominis is a resident of the genitourinary tract; however, its clinical manifestations are uncommon and extragenital. It can cause transient bacteremia with parturition, localized infection in joints, including prosthetic ones, and sternal wound infections after cardiac surgery. M hominis can be grown on chocolate agar from tissue or aspirated fluid obtained sterilely from these sites. Confirmed infections are treated with doxycycline or a fluoroquinolone; they are resistant to macrolides and β-lactams.
The role of Ureaplasma in human disease syndromes remains ill-defined.
This chapter includes two genera of unique microbes that lack a cell wall but otherwise resemble bacteria. They differ from viruses by having both DNA and RNA and by the ability to grow in cell-free media. They are ubiquitous in nature as the smallest of free-living microorganisms. Numerous Mycoplasma species have been isolated from animals and humans, but M pneumoniae stands out as the clearest and most important human pathogen. The other species associated with human disease are summarized in Table 38–1.
TABLE 38–1Features of Pathogenic Mycoplasma and Ureaplasma ||Download (.pdf) TABLE 38–1 Features of Pathogenic Mycoplasma and Ureaplasma
| ||PRIMARY SITE ||MOTILITY ||ATTACHMENT (PROTEINS) ||DISEASE |
|M pneumoniae ||Respiratory ||Gliding ||Terminal organelle (P1, P30) ||Pneumonia |
|M hominis ||Genitourinary || || ||Extra-intestinal infections |
|M genitalium ||Genitourinary ||Gliding ||Terminal organelle (MgPa) ||Urethritis, cervicitis, PID |
|Ureaplasma sp. ||Genitourinary || || ||Role ill-defined as yet |
Mycoplasma and Ureaplasma are taxonomically placed in the Mollicutes, a class of prokaryotes that lack a cell wall. Although their DNA ...