Community-acquired
pneumonia (CAP) is a worldwide
infectious disease caused by bacteria, viruses, or a combination of these infectious agents. Mycoplasma pneumoniae is an atypical
pneumonia pathogen that causes high morbidity and mortality in children, and adenovirus can lead to severe
pneumonia. However, the etiology of different types of
pneumonia is still unclear. In this study, we selected a total of 52 inpatients with M. pneumoniae
pneumonia (MPP) (n = 21), adenovirus
pneumonia (AVP) (n = 16), or
tracheomalacia (n = 15) to serve as a disease control. Bronchoalveolar lavage fluid (BALF) samples that had been obtained for clinical use were analyzed. We compared the differences in microbiota and the expression of 10 inflammatory
cytokines in samples between MPP, AVP, and
tracheomalacia. We found that the bacterial diversity in MPP was lower than that in AVP and
tracheomalacia. Mycoplasma, Streptococcus, and Pseudomonas were predominant in samples of MPP, AVP, and
tracheomalacia, respectively. The expression levels of
IL-6,
IL-8, and
IL-10 were significantly higher in inpatients with AVP compared to children hospitalized with
tracheomalacia or MPP. The lung microbiota in MPP was remarkably correlated with
IL-2,
IL-4,
IL-5,
IL-6, TNF-α, and IL-1α expressions, while this was not found in
tracheomalacia and AVP. Microbiota analysis identified a high load of multi-
drug resistant Acinetobacter baumannii in the lung microbiota of several inpatients, which might be associated with the long hospitalization length and intra-group differences at the individual level. This study will help to understand the microbial etiology of
tracheomalacia, AVP, and MPP and to identify effective
therapies for these diseases.