Genomic Epidemiology and Phenotypic Characterization of Staphylococcus aureus from a Tertiary Hospital in Tianjin Municipality, Northern China.

Staphylococcus aureus remains a dangerous pathogen and poses a great threat to public health worldwide. The prevalence of the S. aureus clonotype is temporally and geographically variable. The genomic and phenotypic characteristics of S. aureus isolates in Tianjin, which is among the four big municipalities in China, are unclear. In the present study, 201 nonduplicate S. aureus isolates, including 70 methicillin-resistant S. aureus (MRSA) and 131 methicillin-susceptible S. aureus (MSSA), were collected from 2015 to 2021 in a tertiary hospital in Tianjin. Whole-genome sequencing of S. aureus isolates was carried out to investigate bacterial molecular characteristics, genomic phylogeny, antimicrobial resistance (AMR) gene carriage, and virulence factor gene distribution. The antibiotic resistance profiles, hemolytic activities, and biofilm formation abilities of the S. aureus isolates were also determined. In total, 31 distinct sequence types (STs) and 68 spa types were identified. ST59 (15.9%, 32/201) was the predominant clonotype, followed by ST398 (14.9%, 30/201) and several other major STs (ST1, ST5, ST6, ST22, ST25, ST188, and the newly emerging ST5527). ST59 and ST5527 mainly included MRSA isolates, while ST398 and the other major STs mainly included MSSA isolates. The unique characteristics of the S. aureus isolates belonging to the major STs were determined. ST59 isolates exhibited strong hemolytic activity, and ST398 strains had high biofilm formation capacity, while ST5527 isolates presented the greatest AMR. The genomic epidemiology and phenotypic characteristics of S. aureus isolates determined in this study will help in disease control in nosocomial environments. IMPORTANCE Staphylococcus aureus is an important bacterium pathogen in tertiary hospitals, which provide rich medical resources. Tianjin is one of the four municipalities in China with a population of more than 13 million. However, the epidemiology and molecular characteristics of S. aureus isolates in Tianjin are unknown. In this study, the genomic and phenotypic analyses were performed to investigate 201 S. aureus isolates collected from a tertiary hospital in Tianjin over a time span of 6 years. The refined analysis of predominant clones ST59, ST398, the newly emerging clone ST5527, as well as other major clones, will undoubtedly aid in the control and prevention of infections caused by S. aureus in tertiary hospitals.