Discussion
MLVA type 4-5-7-2 was a dominant stain of M. pneumoniae in many countries in Asia, Europe, America .14-17 Our results showed a similar result in Henan province of China. The relationship between MLVA types and macrolide-resistant mutation was also shown in our study. MLVA types have no relationship with macrolide-resistant mutation.
The relationship between MLVA types and macrolide resistance mutation have been reported before. In 2015, Xue et al. reported that increasing MRMP in China was linked to the increase of M. pneumoniae strains typed 4-5-7-2,18 and the similar finding was also reported in Hongkong and Japan.19, 20 However, MLVA type 4-5-7-2 is not always related to macrolide-resistance mutation. For example, 4-5-7-2 was also the predominant type in the United States of America, European, Australia, and Thailand,21-24 where the prevalence rate of MRMP was low. The percentage of MRMP among MLVA typed 4-5-7-2 may change with time. In Japan, the percentage of A2063G mutation in M. pneumonia strains typed 4-5-7-2 was only 0.9% between 2004 and 2010, but increased rapidly to 83.8% between 2011 and 2014.19
In this study, the A2063G mutation was the primary mutation, accounting for 100%, no other mutations such as 2064 or 2617 were found. Beside this, our study found mixed infection of wild strain and mutation strain in one sample. Several mixed infections were reported as case reports before.25-27 In these reports, patients were first infected by the macrolide-sensitive M. pneumoniae . After a period of treatment (usually longer than a week), the macrolide-resistance mutation on 23s rRNA was found. However, whether these patients had received macrolide antibiotics before specimen collection was difficult to confirm. So, these patients might have developed macrolide resistance during treatment, or mixed strains might have infected them before specimen collection. More research is needed to do in this area.
Macrolides were the first line pharmaceutics for children with M. pneumoniae infection. Some mutations(A2063 and A2064)are associated with high-level resistance to macrolides,7 widespread use of macrolides for M. pneumoniae with these mutations is not only useless but also dangerous to induce more MRMP. Delayed usage of appropriate antibiotics against MRMP is responsible for poor clinical response and prolonged clinical course.28As a result, severe CAP caused by MRMP will increase. To break this vicious circle, reasonable usage of antibody is important not only in treating the patient but also in preventing further increase of MRMP.
There was a limitation in our study. All samples were from one center in one year. The results of this study should be interpreted cautiously due to possible selection bias.
In conclusion, this is the first study about MLVA profile and its correlation with macrolide resistance in pediatric patients in Henan province. In 2020, M. pneumoniae was responsible for 9.8% pediatric patients with CAP. Macrolide resistance genes was detected in 96% strains in Henan province in 2020. All the MRMP strains carried A2063G mutation (100%). The most common type was 4-5-7-2 ,followed by 3-4-6-2. MRMP was independent to MLVA types.