Mycoplasma pneumoniae, a human respiratory tract pathogen
Mycoplasma pneumoniae is responsible for community-acquired respiratory tract infections, such as tracheobronchitis and pneumonia, particularly in school-aged children and young adults. These infections occur both endemically and epidemically at 3- to 7-year intervals worldwide. Numerous extra-respiratory manifestations of variable severity have also been associated with M. pneumoniae infections including dermatological manifestations and neurological complications.
Detection of M. pneumoniae infections is mainly achieved using molecular-based methods, especially real-time PCR, and serology. Several tests are commercially available. Culture is fastidious, time-consuming, and lacks sensitivity.
Antibiotics with potential activity against M. pneumoniae that are used in human clinical practice include macrolides, tetracyclines and fluoroquinolones. Macrolides represent the 1st-line antimicrobial treatment. Resistance through mutation was reported for in vitro-selected mutants for all these three classes of antibiotics whereas to date, resistance in clinical isolates was only reported for macrolides.
Macrolide resistance in the M. pneumoniae species, which harbors only one ribosomal operon, is defined by mutations in the ribosomal target of the antibiotic, mainly the 23S rRNA gene. The A2058G (Escherichia coli numbering) transition in the peptidyltransferase loop of domain V of 23S rRNA is the most common mutation that is associated with high-level resistance to macrolides. Other substitutions have been reported at position 2058 (A2058C, A2058T), at position 2059 (A2059G, A2059C), at position 2062 (A2062G) and at position 2611 (C2611G, C2611A).
Before 2000, M. pneumoniae infections were easily treated using macrolides because only rare cases of resistance to macrolides had been reported in clinical isolates. Since 2000, macrolide resistance rates have been rising up to 90-100% in Asia, hindering the efficacy of common antibiotic regimens. In North America, Europe and Australia, rates of macrolide resistance have usually remained below 10%. Several molecular methods applicable directly on respiratory specimens were developed to detect macrolide resistance and to circumvent the fastidious isolation of M. pneumoniae from clinical samples.
To date, no tetracycline or fluoroquinolone resistance has been reported in M. pneumoniae clinical isolates. However, because resistant strains have been selected in vitro for both classes of drugs, ongoing monitoring of antibiotic susceptibility of this human respiratory tract pathogen is necessary.
