Although previous studies have reported the dysregulation of respiratory tract microbiota in infectious diseases, insufficient data exist regarding respiratory microbiota imbalances in the lower respiratory tracts (LRTs) of children with Mycoplasma pneumoniae pneumonia (MPP). Here, we analysed the microbial community using 16S rRNA gene sequencing. Finally, bronchoalveolar lavage fluid (BALF) samples from 158 children with MPP and 29 with bacterial or viral pneumonia (control group) were collected. The diversity of the microbial community was significantly different between the two groups. A significantly increased abundance of Tenericutes and Mycoplasma was detected in the MPP group, exceeding 67% and 65% of the total bacterial population, respectively. Using Mycoplasma abundance as the diagnostic method, the sensitivity and specificity of the model was 97.5% and 96.6%, respectively. Compared to the mild MPP group, lower alpha diversity and significantly increased Mycoplasma abundance were found in the severe MPP group ( P < 0.01). The abundance of Mycoplasma was positively correlated with complications and clinical indices in children with severe MPP compared with children with mild MPP. Our study describes the features of the LRT microbiota of children with MPP and uncovered its association with disease severity. This finding may offer insights into the pathogenesis of MPP in children.

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Background More and more studies have shown that high salt intake changed intestinal microbiota and host metabolites. However, no studies have explored the association of a high-salt diet with intestinal microbiota and metabolites in children and adolescents. Therefore, we aimed to explore the relationship between salt intake and intestinal microbiota and host metabolites in Chinese boarding school children and adolescents based on 24-h urinary sodium excretion over three consecutive days. Methods This cross-sectional study was conducted in three boarding schools, from September to October 2021. In 153 children, we analyzed the diversity of intestinal microbiota as well as microbiota composition in normal salt (salt intake < 5.8 g/day) diet and a high salt diet (salt intake ≥ 5.8 g/day) and used linear discriminant analysis effect size analysis to find differential bacterial taxa. Subsequently, we explored the association of salt intake with fecal metabolites and 24-h urinary metabolites in the subgroup analysis. Results The high salt diet was associated with decreased diversity and increased abundance of conditionally pathogenic bacteria that have been linked to metabolic syndromes risk factors, such as Prevotella and Lachnospira (P < 0.05). High salt intake was associated with concentrations of several fecal metabolites, including Isobutyric acid and 2-Furoic acid, and several urinary metabolites such as Proline and Pentadecanoic acid in comparison with the normal salt diet. In addition, these metabolites also showed some correlation with differences in intestinal microbiota due to different salt intake levels. Conclusions Our findings show that the level of salt intake is associated with the intestinal microbiota and host metabolites in children and adolescents, thus providing some basis for explaining the pathogenesis of a high salt diet affecting human health and filling gaps in this area of research in children.