Mycoplasma testing is a diagnostic procedure used to identify infections caused by Mycoplasma, a unique type of bacteria. These microorganisms are considered atypical because they lack a rigid cell wall, a structure found in most other bacteria. This structural difference makes them naturally resistant to common antibiotics, such as penicillin, which target cell wall synthesis. Since Mycoplasma infections often mimic other illnesses, specific laboratory testing is necessary for an accurate diagnosis and to ensure effective treatment is chosen.
Understanding the Mycoplasma Organism
Mycoplasma species are among the smallest known free-living organisms. The absence of a cell wall means they are highly flexible (pleomorphic) and cannot be detected using standard bacterial identification methods like the Gram stain. Their cytoplasmic membranes are durable and contain sterols, which add strength and rigidity.
The species requiring human testing fall into two main groups: respiratory and genitourinary pathogens. Mycoplasma pneumoniae is the most well-known respiratory pathogen, frequently causing “atypical pneumonia,” often called “walking pneumonia,” and other upper respiratory tract illnesses. Mycoplasma genitalium, Mycoplasma hominis, and Ureaplasma species are associated with infections of the reproductive and urinary tracts.
The resistance of Mycoplasma to beta-lactam antibiotics, such as penicillin and cephalosporins, is a direct consequence of their structure. Since these drugs target the cell wall, they are ineffective. Treatment requires different classes of antibiotics, such as macrolides or tetracyclines, which target internal cellular processes.
Clinical Scenarios That Require Testing
Testing is primarily ordered when an infection is not responding to initial, broad-spectrum antibiotic treatment or when symptoms suggest an atypical pathogen.
In the respiratory setting, testing for M. pneumoniae is considered when patients, particularly school-aged children or those in closed communities, have a persistent, non-productive cough, fever, and respiratory symptoms lasting several weeks. This confirms the cause of community-acquired pneumonia, especially when the illness is milder than typical bacterial pneumonia.
For genitourinary infections, testing for species like M. genitalium and Ureaplasma is indicated in cases of persistent urethritis in men not caused by Neisseria gonorrhoeae or Chlamydia trachomatis. In women, testing may be prompted by symptoms like cervicitis, unusual vaginal discharge, or pelvic pain, which can indicate pelvic inflammatory disease (PID). M. genitalium has also been linked to female infertility. Since Ureaplasma and M. hominis can be part of the normal flora in healthy, sexually active individuals, a positive test result must be evaluated alongside the patient’s specific symptoms and clinical context.
Diagnostic Methods and Sample Collection
The preferred methods for Mycoplasma detection focus on identifying the organism’s genetic material. Nucleic Acid Amplification Tests (NAATs), particularly Polymerase Chain Reaction (PCR), are the current standard. NAATs offer high sensitivity and specificity, providing rapid results to guide treatment. These molecular tests amplify small segments of Mycoplasma DNA or RNA, allowing detection of tiny quantities of the organism.
The sample collected depends on the suspected site of infection. For respiratory infections, samples are typically collected using nasopharyngeal or throat swabs. For genitourinary infections, first-catch urine is often collected for M. genitalium testing, or a swab may be taken from the urethra, cervix, or vagina. Samples of blood, joint fluid, or other sterile body fluids may be collected for suspected systemic infections.
Culture-based testing is rarely used for routine diagnosis because the organisms grow very slowly and require specialized media. A negative culture for M. pneumoniae may take three to four weeks to confirm, which is too slow for timely clinical management. Serology, which measures antibodies (IgM and IgG) in the blood, is an alternative method, but its utility is limited by the time required for antibodies to develop and the potential for false-positive results.
Interpreting Test Results and Treatment Context
Interpreting a Mycoplasma test result requires careful consideration of the specific organism, the sample source, and the patient’s symptoms. A positive NAAT result indicates the presence of the organism’s genetic material, confirming infection or colonization. A negative result suggests the organism is absent or present in undetectable quantities. For genital tract samples, a positive result for species like Ureaplasma urealyticum or M. hominis may reflect colonization, as these species can be part of the normal flora in up to 60% of healthy women.
The primary importance of a positive test is dictating appropriate antibiotic therapy. Treatment must focus on macrolides, such as azithromycin, or tetracyclines, like doxycycline. These antibiotics inhibit protein synthesis within the bacterial cell, a mechanism that works regardless of the absence of a cell wall. However, the rising prevalence of macrolide resistance, particularly in M. genitalium, means that treatment may need to be adjusted based on local resistance patterns or subsequent resistance testing.