Molecular epidemiology, genetic diversity, antibiotic resistance and pathogenicity of complex from bacteremia patients in a tertiary hospital in China for nine years.

Background: The complex (Smc) has emerged as a significant nosocomial pathogen contributing to increased mortality rates, particularly in case of bloodstream infections.

Methods: This study employed whole-genome sequencing (WGS) to assess the genetic diversity, antimicrobial resistance profiles, molecular epidemiology and frequencies of virulence genes among 55 isolates obtained from bacteremic cases over a 9-year period.

Results: Based on the threshold of 95% average nucleotide identity (ANI) and 70% digital DNA-DNA hybridization (dDDH) for genospecies delineation, we classified 37 isolates into 6 known species, all belonging to the Smc. The remaining 18 isolates sequenced in this study were assigned to 6 new genomospecies. Among the 55 isolates, we identified 44 different sequence types (STs), comprising 22 known and 22 novel allele combinations. The resistance rate of Smc against trimethoprim-sulfamethoxazole (TMP/SMX) was found to be 3.6%, with the and class one integron integrase genes () detected in these isolates. All Smc isolates were susceptible to minocycline. Furthermore, all Smc strains harbored the genes. Genomospecies 1 (100%,  = 9), (84.21%,  = 19) and (71.43%,  = 7) demonstrated a higher percentage of the gene, which was also associated with a higher separation rate. In addition to , , , genes, all strains (100%) contained , , , and genes, while all genomospecies 1 strains (100%) contained , , and genes.

Conclusion: Our study highlights the genetic diversity among Smc isolates from patients with bacteremia, revealing 22 novel ST types, 58 new alleles and 6 new genomospecies. and were found to carry more virulence factors, emphasizing the importance of accurate strain identification. Minocycline emerged as a promising alternative antibiotic for patients who were resistant to TMP/SMX.