Mycoplasmas are a diverse group of bacteria that are distinguished by their lack of cell walls. There are 3 important human species. Mycoplasma pneumoniae, which causes respiratory tract illness. And Mycoplasma hominis and Ureaplasma urealyticum, which cause genital tract disease.
M. pneumoniae is a common cause of pneumonia in school age children and young adults worldwide. Infections occur in all seasons at a relatively constant rate but occasional large epidemics are experienced. Approximately 10% of community acquired pneumonia cases are said to be due to M. pneumoniae however very few are definitively proven.
The onset of illness is typically gradual with constitutional symptoms such as headache, malaise, sore throat and dry cough. A small proportion of infected individuals go on to have pneumonia, often referred to as atypical pneumonia to distinguish the X-ray appearance from lobar pneumonia caused by Streptococcus pneumoniae.
Laboratory diagnosis is very difficult. The organism grows very slowly making culture an impractical method. Serology may be useful but less reliable than for many pathogens with false negative and false positive results not uncommon. However, new nucleic acid amplification tests show promise.
Cold agglutinins are present (often in large amounts) in approximately 50% of patients and this finding is very suggestive of a diagnosis of Mycoplasma pneumoniae in the proper clinical context.
Erythrocyte sedimentation rate (ESR) is almost always quite elevated during acute illness.
Genital Mycoplasmas (M. hominis and U. urealyticum)
The role that the genital mycoplasmas play in disease is ill defined. Individual consideration is usually not necessary as therapy directed at other, more prominent, pathogens such as Chlamydia pneumoniae usually suffice. However, there is one important exception. U. urealyticum is a well defined cause of non-gonococcal or non-specific urethritis and may be resistant to tetracyclines, the standard therapy for this condition. It should be considered when patients fail tetracycline and alternate agents used (e.g. erythromycin).
In contrast to M. pneumoniae, the genital mycoplasmas are fairly easy to culture. The laboratory must be informed of the intention to culture as special media must be employed. However, interpretations of culture results are difficult as a significant percentage of healthy people are colonized with both organisms.