What is the role of molecular analysis in the workup of Mycoplasma infections (Mycoplasma pneumoniae)?

Updated: Feb 15, 2019
  • Author: Ken B Waites, MD; Chief Editor: Michael Stuart Bronze, MD  more...
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Researchers have developed molecular-based systems for detection of M pneumoniae using polymerase chain reaction (PCR) or other technologies. A variety of gene targets have been described for PCR assays to detect M pneumoniae in clinical specimens. Traditional PCR is gradually being replaced by quantitative real-time PCR assays. Recent publications indicate that the CARDS toxin gene is more sensitive for M pneumoniae detection than assays targeting the P1 protein or ATPase genes. [17]

Some reference laboratories offer PCR assays that they developed themselves for detection of current mycoplasmal infection. Two molecular-based tests for detection of M pneumoniae are now FDA-approved for use in the United States. One of these is the illumigene Mycoplasma assay (Meridian Bioscience, Inc.). This loop-mediated isothermal amplification (LAMP) assay enables detection of M pneumoniae in up to 10 clinical specimens that can be tested simultaneously within one hour after extracted DNA is set up in the incubator/reader. The multiplex Biofire Diagnostics FilmArray RP detects nucleic acids in nasopharyngeal swabs for 20 respiratory tract pathogens, including M pneumoniae, processing one sample at a time, with results in about an hour .

Carriage of mycoplasmas in the upper respiratory tract for variable periods following prior infection may confound the interpretation of a single positive PCR assay result. Furthermore, a PCR assay may reveal very small numbers of organisms that may not be of etiologic significance.

A specific threshold of quantity of mycoplasmas in the respiratory tract that can differentiate colonization from infection has not been established, so a highly sensitive detection method such as PCR performed in a nonquantitative manner may overestimate the clinical importance of M pneumoniae as a pathogen since it often cocirculates with other bacterial and viral respiratory pathogens. For these reasons, molecular-based assays can be accompanied by serological assays for maximum diagnostic accuracy unless testing a normally sterile body fluid in which the presence of any number of mycoplasmas would be considered evidence of disease. [1] Newer quantitative real-time PCR assays alleviate this problem to some degree.

Given the significant limitations of serology, prolonged turnaround time and insensitivity of culture, and the growing availability of rapid diagnosis of mycoplasmal infection in symptomatic patients by molecular-based assays, molecular-based tests are now the preferred method for diagnosis of M pneumoniae infection when available to primary care physicians through a hospital or reference laboratory.

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