It is known that a genetic mutation in domain V of 23S rRNA causes macrolide resistance of Mycoplasma pneumoniae (MP). Recently, the incidence of pneumonia caused by macrolide-resistant MP has increased and various therapeutic approaches for treatment of refractory MP pneumonia have been proposed. However, the pathogenesis of MP pneumonia is not clear, and there are very few studies on the mechanism by which macrolide-resistant mutations lead to a treatment refractory course and the mechanism by which steroid therapy is effective. The purpose of this study was to compare the clinical characteristics of children with MP pneumonia and viral pneumonia, to measure the cytokines in the blood to determine the degree of immune response in children with MP pneumonia and to determine the effect by analyzing the changes in cytokines following steroid adjuvant treatment. In addition, we tried to find out the genetic mutation of the 23S rRNA domain V of MP, and to investigate the clinical characteristics, immune responses according to the genetic mutation.
Pediatric patients admitted for pneumonia at The Catholic University of Korea Daejeon St. Mary's Hospital from September 2019 to March 2020 were included, who had MP detected via multiplex polymerase chain reaction (PCR) and serology. Respiratory specimens were evaluated for PCR and point mutations at positions 2063, 2064 and 2067 in domain V of 23S ribosomal RNA (rRNA). During the nucleotide sequence analysis, the nucleotide sequence was analyzed using three primers for each specimen. 1998-2018 (5'-TCTCGGCTATAGACTCGGTGA -3') and 2020-2132 (5'-TAAGAGGTGTCCTCGCTTCG-3') were used as forward primers, and 2673-2692 (5'-TAAGAGGTGTCCTCGCTTCG-3') was used as a reverse primer. In serum, MP IgM and IgG, IFN-γ, IL-6, TNF-α, IL-10, and IL-1β were measured. Statistical analyses were performed using SPSS software (version 24.0).
Of a total of 62 patients, 53 were diagnosed with MP, and 9 were viral pneumonia. The age of onset of pneumonia was higher in the MP pneumonia group than in the viral pneumonia group, and the fever lasted longer. On chest radiographs, the segmental/lobe pneumonia pattern was more common in the MP pneumonia group, and the bronchial pneumonia pattern was significantly higher in the viral pneumonia group. There was no difference in cytokine values measured in serum between the two groups.
The mutation analysis was performed in 25 of the MP PCR-positive patients. Eighteen (72%) had a mutation A2063G substitution. There was no difference in clinical characteristics or blood tests between 23S rRNA mutation positive and negative groups, but there was mutation in the group with high IFN-γ. In the relationship between cytokines and clinical symptoms, IFN-γ and IL-6 concentrations decreased after steroid adjuvant treatment and were significantly related to clinical indicators such as fever duration after treatment, length of hospital stay and steroid treatment duration. It was thought that it could be used as an index to predict the treatment progress of MP pneumonia.