Bronchoalveolar lavage combined with metagenomic assessment of children hospitalized with Mycoplasma pneumoniae pneumonia

Background: The purpose of this study was to investigate the clinical value of bronchoalveolar lavage (BAL) combined with metagenomic assessment for children hospitalized with Mycoplasma pneumoniae pneumonia (MPP). Methods: This study included children hospitalized with MPP at The Affiliated Women and Children's Hospital of Ningbo University from May 2023 to August 2023. The patients were divided into a moderate M . pneumoniae pneumonia (MMPP) group and a severe M. pneumoniae pneumonia (SMPP) group according to the results of the community-acquired pneumonia (CAP) assessment at admission. All the patients underwent fibre bronchoscopic lavage within 3–7 days after macrolide treatment. Patient throat swab (TS) and bronchoalveolar lavage fluid (BALF) samples were collected for metagenomic next-generation sequencing (mNGS) analysis. The patients were divided into a macrolide-sensitive M. pneumoniae (MSMP) group and a macrolide-resistant M. pneumoniae (MRMP) group according to the presence of macrolide resistance genes in 23S rRNA domain V. The respiratory microbial community diversity was also analysed. Differentially abundant species prediction in TS and BALF samples between the MSMP group and the MRMP group was performed. The maximum-likelihood phylogenetic trees of some patients were also analysed. Results: During the 4-month study, TS and BALF samples were collected from 60 children aged 2-12 years, with a median age of 7 years . On the basis of the CAP assessment results at admission, 48 patients were included in the MMPP group, and 12 patients were included in the SMPP group. The total number of febrile days, D-dimer levels, and procalcitonin (PCT) levels were increased in the SMPP group. On the basis of the mNGS results, these patients were divided into 48 cases of MSMP and 10 cases of MRMP (all cases were A2063G positive). The MP detection rate in TS samples was 92% (55/60), and that in BALF samples was 97% (58/60). The Shannon index of the MRMP group was lower than that of the MSMP group in the BALF samples (p<0.01). The abundance of Actinomyces naeslundii and the relative abundance of MP had optimal predictive performance for MRMP in TS and BALF samples. Five strains (MRMP) from MP12, MP20, MP23, MP48, and MP57 exhibited the closest relationships with the strain M. pneumoniae -15-885, which was isolated in Seoul in 2015. One strain (MSMP) from MP05 was most closely related to the strain M. pneumoniae -E57, which was isolated in Egypt in 2009. Conclusion: MRMP is not the main cause of SMPP-coinfection is. In terms of relative abundance, in MRMP patients, MP is dominant in BALF specimens. TS specimens cannot replace BALF samples for determining the aetiology of MPP. A. naeslundii and the relative abundance of MP are optimal biomarkers for predicting whether a case is MRMP in TS samples and BALF samples, respectively. The majority of the MRMP strains from this study are closely related to the strain isolated in Seoul in 2015.