Mycoplasma

There are two completely different types of infections caused by Mycoplasma: one respiratory (M. pneumoniae) and one in the genital tract (M. genitalium and other species). This will influence the type of samples collected.

Blood tests for antibody (M. pneumoniae only)
Two types of antibodies produced in response to an M. pneumoniae infection may be measured in the blood, IgM and IgG. IgM antibodies are the first to be produced by the body in response to infection. Levels of IgM rise for a short time period and then decline, often remaining detectable in the blood for several months. IgG antibody production follows IgM production, rising over time, and then stabilising. Once a person has had a mycoplasma infection, they will typically have some measurable amount of mycoplasma IgG antibody in their blood for the rest of their life. In order to diagnose an active M. pneumoniae infection, a doctor may initially request both M. pneumoniae IgM and IgG antibody tests and then collect another sample two to four weeks later to retest for M. pneumoniae IgG. This combination of tests is used so that the change in the amount of IgG can be evaluated and because some people, especially infants and those with compromised immune systems, may not produce expected amounts of IgG or IgM.

Direct detection (both M. pneumoniae and M. genitalium)
Mycoplasma detection involves finding the microorganism in the respiratory secretions, blood, fluid, urine, tissue sample or swabs. This can be done either by culturing the mycoplasma in a supportive environment or by detecting its genetic material (DNA).

A mycoplasma culture is the traditional method of detection, but it can be challenging and is not always successful. The test involves inoculating a nutrient media with the patient's sample and incubating the culture in a specialised growth media. There are specific nutritional needs that must be met to promote the growth of the microorganisms, and they can be slow to grow (weeks).

DNA testing is a rapid (few days) and sensitive method and it is now becomingmore commonly used in UK laboratories.

• M. pneumoniae DNA testing may sometimes be requested, along with other tests, such as testing for Chlamydia pneumoniae, Bordetella pertussis, and Legionella species to help distinguish between these organisms as the cause of a respiratory infection.
• M. genitalium DNA testing is also becoming common in many UK laboratories and sexual health clinics
• Occasionally, testing may be used to determine if Mycoplasma hominis or Ureaplasma urealyticum is the cause of an infection of the genital or urinary tract. M. hominis and U. urealyticum genital samples are typically tested using a culture method that takes several days to recover the microorganisms, but M. genitalium, which can take 1-2 months to grow, may be more reliably detected with DNA testing. Some laboratories may also offer DNA testing for Ureaplasma but this is not very common yet.

The choice of tests and body samples collected depends on the age of the patient, their general health status and symptoms, and on the doctor's clinical findings and suspicions of organ involvement. A person with a suspected mycoplasma infection may be treated based upon clinical findings, and imaging studies with or without laboratory testing.

M. pneumoniae testing may be requested when someone has severe respiratory symptoms that are not due to a typical bacterial infection, such as pneumococcal pneumonia. Some of these symptoms may include:

• Non-productive cough that may persist for several weeks
• fever
• sore throat
• headaches and muscle aches

Testing may be done when an infection spreads to the lower respiratory tract, causing "walking pneumonia," and/or spreads to other parts of the body and causes complications such as rash, arthritis, encephalitis, inflammation of the heart muscle or the lining that surrounds the heart or haemolytic anaemia, and when a person is not responding to standard treatments. It may also be used to help track and control the spread of M. pneumoniae infections during an outbreak.

Testing for other species of mycoplasma may be performed, in addition to M. pneumoniae testing, when very young infants and those with compromised immune systems have lung and/or systemic infections or complications that could be due to a mycoplasma infection.

In general, IgM and IgG testing is performed when a doctor suspects that a person has an active M. pneumoniae infection, and another IgG test may be performed 2-4 weeks later to document a rise in antibody levels in response to an infection. A M. pneumoniae culture and sometimes a DNA test may also be used when an active infection is suspected.

Testing of genital samples is now becoming more common in many sexual health clinics in UK. M. genitalium DNA testing and/or culture for M. hominis and U. urealyticum may sometimes be requested when a sexually active male has inflammation of the urethra that is not due to gonorrhoea or chlamydia (non-gonococcal urethritis, NGU) or when a female is suspected of having a genital mycoplasma infection, after tests for gonorrhoea and chlamydia have come back negative.

Antibody testing
Significant concentrations of M. pneumoniae IgM and/or a four-fold increase in IgG levels between the initial sample and the convalescent sample indicate an active or recent M. pneumoniae infection. Increases in IgG, without IgM, can also be seen with a re-infection.

If neither IgM or IgG are present in detectable concentrations, then it either means that a person does not have an active infection, has not had a mycoplasma infection (recent or in the past), or that the person's immune system has not produced antibodies in response to the microorganism.

Direct detection (culture or DNA testing)
The detection of one of the mycoplasmas or U. urealyticum in a cultured sample may indicate that the person has a mycoplasma infection, particularly if the sample is from a body site that is normally sterile, such as joint fluid or blood. Correlation with clinical symptoms is always important in case of isolation from other sites (i.e. respiratory or genital tract) and your doctors will decide if such isolation is relevant to your current symptoms.
If mycoplasma is not detected in a culture, then it may mean that the person is not infected by that microorganism or that the organism was not present in sufficient quantity to be detected in the sample tested.

With DNA testing (both M. pneumoniae and M. genitalium), if the mycoplasma is present in the sample, then the person may have an infection caused by the organism, but correlation with clinical symptoms is important. If it is not detected, then the person may not have a Mycoplasma infection or the microorganism was present in numbers too low to be detected.

Mycoplasma infections often cause symptoms that resemble viral infections, but they respond to antibiotic treatment, with a decrease in the duration of symptoms.

Having a mycoplasma infection does not confer immunity. A person can become re-infected.

Mycoplasmas cannot be seen under the microscope on a gram stain, a test that is often used to help identify bacteria.

An older test called "cold agglutinins" may sometimes be requested to help detect a M. pneumoniae infection. It is based on the concept that during an active mycoplasma infection, an antibody is produced in the blood that will cause red blood cells to clump together when cooled. This test is not specific for mycoplasma, but more than half of those with a M. pneumoniae infection will have significant amounts of cold agglutinins.

They are a common but often unidentified cause of infections. Like the viruses that cause the common cold, they tend to cause mild to moderate, nonspecific cold symptoms in most people, and in most cases they are self-limited, resolving without treatment or with prescribed antibiotics.