MP is one of the most common pathogens identified in CAP patients at home and abroad[1, 12], and is more prevalent in children ≥ 5 years of age than those < 5 years of age[2]. In this study, the majority of children in the MR and MS groups (67.9% and 58.33%) were older than 5 years of age. Furthermore, the overall percentage of MRMP has progressively grown in China[8, 13], and MRMP has also emerged in other countries among children[14, 15]. MRMP is strongly associated with the emergence of point mutations in the 23S rRNA gene[16, 17]. In this study, the A2063G mutation in domain V of 23S rRNA was identified in all patients. This is a consistent with many population-based epidemiological studies, which revealed that A2063G mutations accounted for ≥ 99.0% of cases[8, 13, 18].
MRMP patients have a longer duration of fever and more prolonged hospitalization than macrolide-sensitive MP patients[18, 19]. However, the mutation in the 23S rRNA gene showed no statistical association with fever duration following macrolide therapy or the length of hospitalization in this study. Yoon IA.et al also demonstrated that macrolide resistance had no effect on MPP fever duration[20]. We hypothesize this is the result of the following reasons.
First, Deng et al. demonstrated that there was no correlation between radiographic findings and the A2063G mutation in the 23S rRNA gene of MPP patients[21]. Radiologic findings revealed a determinant effect on the clinical course, such as fever duration of MPP[20]. Hence, the 23S rRNA mutations may not have an impact on the clinical course of MPP, and MPP patients with these mutations may be not necessarily resistant to macrolides. All of the children with the A2063G mutation in our study received azithromycin therapy and discharged after improvement. Macrolide antibiotics may therefore be used as a therapeutic for MPP patients with the A2063G mutation.
What’s more, macrolides bind to 50S ribosomes in prokaryotic and eukaryotic organisms to exert their antibacterial activity by preventing nascent peptides from translocating or transpeptidation. However, some articles have suggested that the A2063G mutants had high levels of resistance to erythromycin and azithromycin[22]. MPP is self-limiting disease, and there is growing evidence that macrolide antibiotics are not just antimicrobials but also have immunomodulatory effects[23, 24]. Azithromycin prevents the transcription factors nuclear factor-kappa B or activator protein-1, which may be the reason behind their inhibition of the synthesis of various pro-inflammatory cytokines, including interleukin (IL)-1, IL-6, IL-8, and tumor necrosis factor-alpha[25]. The amelioration of clinical symptoms, including fever, may have been facilitated by the immunomodulatory actions of macrolides, which requires more reports to evaluate the anti-inflammatory effects of macrolides in MRMP.
Last but not least, we cannot overlook the function of hormones. Though it's still unclear what exactly causes the cytokine and hyperinflammatory reactions that follow lung damage from MP infection[7, 26], some studies have demonstrated that hormones therapy has improved outcomes and prevented disease progression in MPP patients[27, 28]. Hormones were used in about 52.75% patients in this study and the role of hormones cannot be ignored. However, Han et al. suggested that there was no significant difference in clinical or laboratory markers between macrolide-resistant and macrolide-sensitive MPP treated with hormones [29]. Likewise, Hormones were not associated with the length of hospitalization or fever in this paper. The reason may be the dosing of hormones[30]. Our population used a low dose of hormones. Further studies on the role of hormones and different doses of hormones in MPP are needed.
There are certain drawbacks to our study. First, the sample-collection period—which spanned just 10 months, from January to October 2023—was brief. However, this is the optimal annual time period for MPP cases, and there was a sizable sample obtained. Second, this was a single-center study and may be deemed inadequate for MPP in general. Multi-center investigations with larger sample are needed. Furthermore, no antimicrobial susceptibility testing was completed. But macrolide-resistant gene were identified by tNGS based on ultra-multiplex PCR amplification and high-throughput sequencing technology. Lastly, we did not compare the efficacy of other antibiotics including tetracyclines and fluoroquinolones, with macrolides in MPP. We'll carry out relevant research in this area.