Mycoplasma

Mycoplasma testing is primarily used to help determine if Mycoplasma pneumoniae is the cause of a respiratory tract infection. It may also be used to help diagnose a systemic infection that is thought to be due to mycoplasma.

Blood tests for antibody to M. pneumoniae
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 stabilizing. 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 health practitioner may order both M. pneumoniae IgM and IgG antibody tests as acute samples and then collect another M. pneumoniae IgG test two to four weeks later as a convalescent sample. This combination of tests is ordered 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
M. pneumoniae detection involves finding the microbe in the respiratory secretions, blood, fluid, or tissue sample. 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. Culturing mycoplasma is more difficult than culturing common bacteria such as staphylococci or streptococci. Mycoplasma lack cell walls and do not grow well on routine bacterial culture media. They lack cell walls and cannot be visualized with a Gram stain as done with most bacteria. Growing mycoplasma involves incubating the patient’s sample in a special nutrient media to promote the growth of these microbes, which are slow to grow.

A negative M. pneumoniae culture must be held for 3-4 weeks to confirm that a mycoplasma is not present, compared to 2-4 days for most bacteria. Antibody testing, or sometimes DNA testing, is usually ordered in addition to, or instead of, a M. pneumoniae culture because of this long incubation period before results can be released.

DNA testing is rapid and sensitive but was not routinely offered in many microbiology laboratories because there was not a commercial source for the test. Now there are syndromic panels available that allow the detection of multiple respiratory pathogens that include M. pneumoniae and that will increase the ability of laboratories to test for this microbe. However, the detection of mycoplasma DNA does not confirm a current infection. The presence of mycoplasma DNA may indicate the microbe is colonizing a person or mycoplasma DNA may be detectable after the symptoms of infection have resolved and the organisms are no longer viable.

M. pneumoniae DNA testing may sometimes be ordered, 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.

Occasionally, testing may be used to determine if Mycoplasma hominis, Mycoplasma genitalium, 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 microbes, but M. genitalium, which can take 1-2 months to grow, may be more reliably detected with DNA testing.

The choice of tests and body samples collected depends on the age of the person being tested, their general health status and symptoms, and on the healthcare practitioner’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 ordered 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:

• Nonproductive 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 hemolytic anemia, and when a person is not responding to standard treatments. It may also be ordered 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 are performed when a health practitioner 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 a DNA test may also be ordered when an active infection is suspected.

Testing of genital samples is not often done because mycoplasmas are frequently part of the normal flora of the genital tract. However, a culture for M. hominis and U. urealyticum may sometimes be ordered when a sexually active male has inflammation of the urethra that is not due to gonorrhea or chlamydia (non-gonococcal urethritis, NGU) or when a female is suspected of having a genital mycoplasma infection, after tests for gonorrhea 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 means that a person being tested either 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 microbe.

Direct detection
The detection of one of the mycoplasmas or U. urealyticum in a cultured sample may indicate that the person being tested has a mycoplasma infection, particularly if the sample is from a body site that is normally sterile, such as joint fluid or blood. However, if the sample is from the respiratory tract or the genital tract, a positive culture may also mean that the mycoplasma is present as part of their normal flora. For example, U. urealyticum is present in the genital tract of about 60% of healthy women and M. hominis is present in about 20%.

If mycoplasma is not detected in a culture, then it may mean that the person is not infected by that microbe or that the organism was not present in sufficient quantity to be detected in the sample tested.

With DNA testing for M. pneumoniae, if the mycoplasma is present in the sample, then the person may have M. pneumoniae or may be colonized by the organism. If it is not detected, then the person may not have a M. pneumoniae infection or the microbe was present in numbers too low to be detected.

Mycoplasma infections often cause symptoms that resemble viral infections. Unlike viruses, they respond to specific antibiotics that treat this type of microbe and decrease 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 ordered 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 respiratory 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.

Mycoplasmas are very common in the environment and it is not always possible to prevent infection. Those caused by outbreaks of Mycoplasma pneumoniae are transmitted through respiratory droplets and may be avoided through good hand washing, covering the nose and mouth when coughing or sneezing, and avoiding close contact with sick people. Mycoplasmas that are passed through sexual contact can be prevented in the same manner as other sexually transmitted diseases (STDs). Those passed from mother to baby are difficult to predict or prevent.

Samples may be collected in your healthcare practitioner’s office, but testing requires specialized equipment and will need to be done in a hospital or reference laboratory.