Wei Tang,1,2,* Ying Liu,3,* Xin Li,2 Guiyun Leng,2 Ju Gao,2 Yawu Wang,2 Jie Yao,2 Zhou Liu,2 Qiang Zhou,2 Yuanhong Xu1 

1Department of Clinical Laboratory, The First Affiliated Hospital of Anhui Medical University, Hefei, 230022, People’s Republic of China; 2Department of Clinical Laboratory, The Second Affiliated Hospital of Anhui Medical University, Hefei, 230601, People’s Republic of China; 3High Magnetic Field Laboratory, Hefei Institutes of Physical Science, Chinese Academy of Sciences, Hefei, 230031, People’s Republic of China

*These authors contributed equally to this work

Correspondence: Yuanhong Xu, Department of Clinical Laboratory, The First Affiliated Hospital of Anhui Medical University, 218 Jixi Road, Shushan District, Hefei, Anhui, 230022, People’s Republic of China, Tel +86 135 0569 4447, Fax +86 551 6292 2125, Email xyhong1964@ahmu.edu.cn

Purpose: This study aimed to investigate the microbiological characteristics of clinically isolated Staphylococcus aureus with different hemolytic phenotypes in China.
Materials and Methods: Using the three-point inoculation method, the hemolytic phenotypes of 1295 clinically isolated S. aureus strains were detected and categorized. Antimicrobial susceptibility testing of all strains was performed using a VITEK 2 Compact System. After sample size matching, plasma coagulase activity, catalase activity, mRNA expression of hemolysin genes (hla, hlb, hlc, and hld), biofilm formation, growth kinetics, inflammatory response of macrophages and cytotoxicity of S. aureus with different hemolytic phenotypes using the rabbit plasma kit, the catalase test on slides, qRT-PCR, crystal violet staining, the microcultivation assay, the ELISA kits, and the CCK-8 assay, respectively.
Results: Seven categories of hemolytic phenotypes were identified. Accordingly, strains were categorized into seven different groups, including S. aureus with complete hemolytic phenotype (SCHP), S. aureus with weak hemolytic phenotype (SWHP), S. aureus with incomplete hemolytic phenotype 1 (SIHP-1), SIHP-2, SIHP-3, SIHP-4 and SIHP-5, the last three of which were reported for the first time. Except for the hemolytic phenotype, all seven groups differed in clinical isolation rates, antibiotic resistance profile, plasma coagulase activity, mRNA expression of hemolysin genes, biofilm formation, growth kinetics, inflammatory response of macrophages, and cytotoxicity.
Conclusion: S. aureus with different hemolytic phenotypes have distinctive microbiological characteristics. Clinical microbiologists need to be vigilant about the hemolytic phenotypes when culturing S. aureus strains, and actively enhance communication with clinicians to optimize the treatment of infection.

Keywords: Staphylococcus aureus, hemolytic phenotype, hemolysin, microbiological characteristics, antibiotic resistance