Genotypic and phenotypic characteristics of group B streptococcal isolates from neonates in a tertiary hospital in Qingyang, Gansu Province, China.

Group B Streptococcus (GBS) causes severe neonatal infections, leading to high mortality rates. This study aimed to investigate the genetic characteristics of GBS isolates in a hospital setting. Nineteen isolates were identified through a review of preservation and cultivation processes since January 2022, followed by antibiotic susceptibility testing. Whole-genome sequencing (WGS) was used to investigate genetic relationships. Among 19 isolates, serotype V was the most prevalent (n = 7), followed by Ib (n = 6) and III (n = 6). Genomic sequence analysis revealed that 19 isolates belonged to four sequence types (STs) related to four clonal complexes (CCs), namely CC12, CC19, CC327, and CC452. The isolates exhibited high resistance rates to erythromycin (89 %, n = 17), levofloxacin (79 %, n = 15), clindamycin (68 %, n = 13), and tetracycline (53 %, n = 10). The mreA gene was found in all GBS isolates (100 %), while the most prevalent resistance gene was ermB (84 %). Furthermore, the fbsB virulence gene associated with adherence was identified in four serotype V/ST890 GBS isolates. Two isolates with different sequence types (ST10, ST19) were found to have undergone parallel mutations in the gene SE858_09425, which encodes a DNA translocase FtsK. Both exhibited an I259L substitution in a conserved ligand-binding domain, strongly suggesting this site is critical for adaptive evolution. IMPORTANCE: Group B Streptococcus (GBS) is a major pathogen causing severe neonatal infections, such as sepsis and meningitis, with high mortality and morbidity rates. The rising antimicrobial resistance of GBS presents significant challenges for clinical management. This study investigates 19 GBS isolates isolated from neonates in Qingyang, Gansu, focusing on their genetic characteristics and resistance profiles through molecular epidemiological analysis and WGS. The findings offer critical insights into the molecular mechanisms of GBS infections, which can inform infection control measures, improve prevention strategies, and optimize antimicrobial therapies to enhance neonatal healthcare outcomes.