Mycoplasmas are the smallest free-living microorganisms known. They are unlike other types of bacteria (atypical) in many ways and can be difficult to culture and identify. Mycoplasmas may be part of the normal flora found in the throat, upper respiratory tract, and genitourinary tract.
Mycoplasma testing is most often used to detect Mycoplasma pneumoniae (M. pneumoniae), the causative agent of respiratory infections often referred to as "atypical pneumonia." M. pneumoniae is a common cause of upper respiratory infections, with an estimated 2 million cases in the U.S. each year. It is responsible for 15-20% of cases of community-acquired pneumonia, appearing as single cases and as periodic epidemics – especially in school-age children and in closed populations such as the military. Infections can occur at any time of the year, but outbreaks are more prevalent in the late summer and early fall.
Most cases of M. pneumoniae infection are mild and self-limited, causing nonspecific symptoms such as bronchitis, a runny nose, and a nonproductive cough that may persist for several weeks. Symptoms may become more severe, causing fever, sore throat, headaches, and muscle aches, when the infection spreads to the lower respiratory tract and causes "walking pneumonia," or, more rarely, spreads to other parts of the body. This is especially true in very young infants, in those who have underlying health conditions, such as asthma, or who have compromised immune systems, such as those with HIV/AIDS. Depending upon what parts of the body become infected, complications may range from meningitis to difficulty breathing, cardiac inflammation and arrhythmia, skin rashes, lesions or nodules, arthritis, anemia, or to Guillain-Barré syndrome.
Testing may occasionally be done to detect other types (species) of mycoplasma. Mycoplasma hominis, Mycoplasma genitalium and Ureaplasma urealyticum (a closely related group of microorganisms) infections are less common than those seen with M. pneumoniae. In adults, these organisms are primarily sexually transmitted, causing nongonococcal urethritis (NGU) and some inflammation of the prostate (prostatitis) in men and sometimes associated with vaginal discharge and pelvic inflammatory disease (PID) in women. M. hominis and U. urealyticum can be passed from mother to baby during birth when the baby passes through an infected birth canal. They typically colonize infants for their first couple of years. Rarely, they can cause systemic infections in infants and in those with compromised immune systems.
How is the sample collected for testing?The sample required depends on whether testing is done to determine the presence of antibody or to detect the microorganism itself and on the health status of the patient.
Antibody testing requires a blood sample, obtained by inserting a needle into a vein in the arm.
Direct detection of mycoplasma may be done on a variety of samples. For a respiratory infection, samples may include sputum, a washing of the bronchi in the lungs, or throat swab. If a systemic infection is being diagnosed, blood, joint fluid, body fluids, or tissues samples may be cultured. Some samples may require a special procedure to collect them. To detect a genital infection, a swab of the cervix or urethra may be collected.
Is any test preparation needed to ensure the quality of the sample?No test preparation is needed.
How is it used?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 doctor 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.
M. pneumoniae detection involves finding the microorganism 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. The test involves inoculating a nutrient media with the patient's sample and incubating the culture in a specialized 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. For instance, a negative M. pneumoniae culture must be held for 3-4 weeks to confirm that mycoplasma is not present. Antibody testing, or sometimes DNA testing, is usually ordered in addition to, or instead of, a M. pneumoniae culture.
DNA testing is rapid and sensitive but is not widely used in the diagnosis of mycoplasma infections. This is due, in part, to the fact that it can be difficult to distinguish between a mycoplasma that is colonizing a person from one that is causing an infection and due to the fact that 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 microorganisms, 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 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.
When is it ordered?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
- 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 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 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.
What does the test result mean?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.
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. 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 microorganism 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 microorganism was present in numbers too low to be detected.
Is there anything else I should know?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.
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.
Why haven't I heard about mycoplasmas?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.
Can mycoplasma infections be avoided?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.
On This Site
Elsewhere On The Web
American Lung Association: Understanding Pneumonia
Nemours Foundation, KidsHealth: Pneumonia
MedlinePlus Medical Encyclopedia: Mycoplasma Pneumonia
New York State Department of Health: Mycoplasma Infection Factsheet
Centers for Disease Control and Prevention: Diseases Characterized by Urethritis and Cervicitis
Cleveland Clinic: Ureaplasma & Mycoplasma Infections
Cleveland Clinic: Nongonococcal Urethritis (NGU) in Men