Mycoplasma pneumoniae causes community-acquired respiratory tract infections, particularly in school-aged children and young adults. These infections occur both endemically and epidemically worldwide. M. pneumoniae lacks cell wall and is subsequently resistant to beta-lactams and to all antimicrobials targeting the cell wall. This mycoplasma is intrinsically susceptible to macrolides and related antibiotics, to tetracyclines and to fluoroquinolones. Macrolides and related antibiotics are the first-line treatment of M. pneumoniae respiratory tract infections mainly because of their low MIC against the bacteria, their low toxicity and the absence of contraindication in young children. The newer macrolides are now the preferred agents with a 7-to-14 day course of oral clarithromycin or a 5-day course of oral azithromycin for treatment of community-acquired pneumonia due to M. pneumoniae, according to the different guidelines worldwide. However, macrolide resistance has been spreading for 15 years worldwide, with prevalence now ranging between 0% and 15% in Europe and the USA, approximately 30% in Israel and up to 90%-100% in Asia. This resistance is associated with point mutations in the peptidyl-transferase loop of the 23S rRNA and leads to high-level resistance to macrolides. Macrolide resistance-associated mutations can be detected using several molecular methods applicable directly from respiratory specimens. Because this resistance has clinical outcomes such as longer duration of fever, cough and hospital stay, alternative antibiotic treatment can be required, including tetracyclines such as doxycycline and minocycline or fluoroquinolones, primarily levofloxacin,,during 7 to 14 days, even though fluoroquinolones and tetracyclines are contraindicated in all children and in children <8 year-old, respectively. Acquired resistance to tetracyclines and fluoroquinolones has never been reported in M. pneumoniae clinical isolates but reduced susceptibility was reported in in vitro selected mutants. This article focuses on M. pneumoniae antibiotic susceptibility and on the development and the evolution of acquired resistance. Molecular detection of resistant mutants and therapeutic options in case of macrolide resistance will also be assessed.

Mycoplasma hominis is an opportunistic human mycoplasma. Two other pathogenic human species, M. genitalium and Ureaplasma parvum, reside within the same natural niche as M. hominis: the urogenital tract. These three species have overlapping, but distinct, pathogenic roles. They have minimal genomes and, thus, reduced metabolic capabilities characterized by distinct energy-generating pathways. Analysis of the M. hominis PG21 genome sequence revealed that it is the second smallest genome among self-replicating free living organisms (665,445 bp, 537 coding sequences (CDSs)). Five clusters of genes were predicted to have undergone horizontal gene transfer (HGT) between M. hominis and the phylogenetically distant U. parvum species. We reconstructed M. hominis metabolic pathways from the predicted genes, with particular emphasis on energy-generating pathways. The Embden–Meyerhoff–Parnas pathway was incomplete, with a single enzyme absent. We identified the three proteins constituting the arginine dihydrolase pathway. This pathway was found essential to promote growth in vivo. The predicted presence of dimethylarginine dimethylaminohydrolase suggested that arginine catabolism is more complex than initially described. This enzyme may have been acquired by HGT from non-mollicute bacteria. Comparison of the three minimal mollicute genomes showed that 247 CDSs were common to all three genomes, whereas 220 CDSs were specific to M. hominis, 172 CDSs were specific to M. genitalium, and 280 CDSs were specific to U. parvum. Within these species-specific genes, two major sets of genes could be identified: one including genes involved in various energy-generating pathways, depending on the energy source used (glucose, urea, or arginine) and another involved in cytadherence and virulence. Therefore, a minimal mycoplasma cell, not including cytadherence and virulence-related genes, could be envisaged containing a core genome (247 genes), plus a set of genes required for providing energy. For M. hominis, this set would include 247+9 genes, resulting in a theoretical minimal genome of 256 genes. Mycoplasma hominis, M. genitalium, and Ureaplasma parvum are human pathogenic bacteria that colonize the urogenital tract. They have minimal genomes, and thus have a minimal metabolic capacity. However, they have distinct energy-generating pathways and distinct pathogenic roles. We compared the genomes of these three human pathogen minimal species, providing further insight into the composition of hypothetical minimal gene sets needed for life. To this end, we sequenced the whole M. hominis genome and reconstructed its energy-generating pathways from gene predictions. Its unusual major energy-producing pathway through arginine hydrolysis was confirmed in both genome analyses and in vivo assays. Our findings suggest that M. hominis and U. parvum underwent genetic exchange, probably while sharing a common host. We proposed a set of genes likely to represent a minimal genome. For M. hominis, this minimal genome, not including cytadherence and virulence-related genes, can be defined comprising the 247 genes shared by the three minimal genital mollicutes, combined with a set of nine genes needed for energy production for cell metabolism. This study provides insight for the synthesis of artificial genomes.

Background: Mycoplasma pneumoniae respiratory infections are transmitted by aerosol and droplets in close contact. Aim: We investigated global M. pneumoniae incidence after implementation of non-pharmaceutical interventions (NPIs) against COVID-19 in March 2020. Methods: We surveyed M. pneumoniae detections from laboratories and surveillance systems (national or regional) across the world from 1 April 2020 to 31 March 2021 and compared them with cases from corresponding months between 2017 and 2020. Macrolide-resistant M. pneumoniae (MRMp) data were collected from 1 April 2017 to 31 March 2021. Results: Thirty-seven sites from 21 countries in Europe, Asia, America and Oceania submitted valid datasets (631,104 tests). Among the 30,617 M. pneumoniae detections, 62.39% were based on direct test methods (predominantly PCR), 34.24% on a combination of PCR and serology (no distinction between methods) and 3.37% on serology alone (only IgM considered). In all countries, M. pneumoniae incidence by direct test methods declined significantly after implementation of NPIs with a mean of 1.69% (SD ± 3.30) compared with 8.61% (SD ± 10.62) in previous years (p < 0.01). Detection rates decreased with direct but not with indirect test methods (serology) (–93.51% vs + 18.08%; p < 0.01). Direct detections remained low worldwide throughout April 2020 to March 2021 despite widely differing lockdown or school closure periods. Seven sites (Europe, Asia and America) reported MRMp detections in one of 22 investigated cases in April 2020 to March 2021 and 176 of 762 (23.10%) in previous years (p = 0.04). Conclusions: This comprehensive collection of M. pneumoniae detections worldwide shows correlation between COVID-19 NPIs and significantly reduced detection numbers.

Mycoplasma pneumoniae is a pathogenic mycoplasma responsible for respiratory tract infections in humans, which occurs worldwide in children and adults. This article focuses on its antibiotic susceptibility profile and on the development of acquired resistance in this microorganism. The lack of a cell wall in mycoplasmas makes them intrinsically resistant to β-lactams and to all antimicrobials that target the cell wall. M. pneumoniae is susceptible to macrolides and related antibiotics, tetracyclines and fluoroquinolones. Macrolides and related antibiotics are the first-line treatment for respiratory infections caused by M. pneumoniae. However, strains with acquired resistance to macrolides have recently emerged worldwide and have been spreading in Europe, USA and A sia especially, with more than 90% of Chinese isolates resistant to erythromycin and azithromycin. This acquired resistance can be detected by PCR methods directly from respiratory specimens and is related to 23S rRNA mutations.

Inflammasomes are intracellular multiprotein signaling complexes that activate Caspase-1, leading to the cleavage and secretion of IL-1β and IL-18, and ultimately host cell death. Inflammasome activation is a common cellular response to infection; however, the consequences of inflammasome activation during acute infection and in the development of long-term protective immunity is not well understood. To investigate the role of the inflammasome in vivo, we engineered a strain of Listeria monocytogenes that ectopically expresses Legionella pneumophila flagellin, a potent activator of the Nlrc4 inflammasome. Compared with wild-type L. monocytogenes , strains that ectopically secreted flagellin induced robust host cell death and IL-1β secretion. These strains were highly attenuated both in bone marrow-derived macrophages and in vivo compared with wild-type L. monocytogenes . Attenuation in vivo was dependent on Nlrc4, but independent of IL-1β/IL-18 or neutrophil activity. L. monocytogenes strains that activated the inflammasome generated significantly less protective immunity, a phenotype that correlated with decreased induction of antigen-specific T cells. Our data suggest that avoidance of inflammasome activation is a critical virulence strategy for intracellular pathogens, and that activation of the inflammasome leads to decreased long-term protective immunity and diminished T-cell responses.

Mycoplasma pneumoniae is a common aetiological agent of community-acquired respiratory tract infections for which macrolides are the treatment of choice. In France, only two macrolide-resistant isolates were reported in 1999. In contrast, several recent data reported that macrolide-resistant M. pneumoniae isolates have been spreading since 2000 in Japan. Mutations A2058G (Escherichia coli numbering), A2058C, A2059G, A2062G, C2611A and C2611G in domain V of the 23S rRNA gene were associated in vivo or in vitro with this resistance. The aim of this study was to determine whether macrolide resistance of M. pneumoniae is emerging in France. We developed a duplex real-time PCR for the detection of the six 23S rRNA mutations associated with macrolide resistance in M. pneumoniae and a simplex real-time PCR for the identification of the A2058G mutation, the most common one. Both methods rely on fluorescence resonance energy transfer coupled to melting curve analysis and are directly applicable to clinical samples. The duplex real-time PCR assay, first validated on 40 genetically characterized M. pneumoniae strains, was then applied directly on 248 French respiratory tract clinical samples. Among M. pneumoniae-positive specimens collected before 2005, no macrolide-resistant M. pneumoniae isolate was detected. In contrast, among 51 samples collected between 2005 and 2007, five (9.8%) yielded a resistant genotype, suggesting a recent increase in macrolide-resistant M. pneumoniae isolates in France. The epidemiological monitoring of macrolide resistance in this species has become necessary in France and Europe, and will be made easier by using these PCR assays.