[Analysis of pathogenic features of mucoid

Whole-genome sequencing, serotype typing, MLST typing, population genetic structure analysis, and core-genome single nucleotide polymorphism (cgSNP) analysis were performed on 23 strains of mucoid Haemophilus influenzae collected from the Laboratory Center of Hunan Children's Hospital from January 2021 to December 2022. Drug susceptibility tests were conducted using the automated microbial identification and susceptibility analysis system AF-600, and virulence genes and drug resistance genes were analyzed based on the whole-genome sequences. Based on the serotype typing of whole-genome sequencing, all 23 strains were Haemophilus influenzae type b (Hib). MLST analysis revealed that the 23 strains belonged to six ST types, among which 10 strains (43.5%) were ST386, 5 strains (21.7%) were ST18, and 2 strains (8.7%) were the newly discovered ST2887. Bayesian population structure analysis (BAPS) showed three distinct populations. The results of the virulence gene analysis showed that the carriage rates of genes encoding capsule-related proteins and those associated with bacterial immune regulation and inflammatory signaling pathways were all 100%. However, the ompP5 gene related to bacterial adhesion, and the hgpC and hxuA genes related to bacterial protein metabolism were all present in the newly discovered ST2887. The in vitro drug susceptibility test results of 23 strains of mucoid Hib showed that the resistance rates to ampicillin, cefuroxime, and Trimethoprim-sulfamethoxazole were 13.0%(3 strains), 13.0%(3 strains), and 87.0%(20 strains), respectively. They were sensitive to other beta-lactam drugs. All the 23 strains of mucoid Haemophilus influenzae infected children were Hib, and the main ST types were ST386 and ST18. It is very important to advocate Hib vaccination.