First Report of Oxacillin Susceptible mecA-Positive Staphylococcus aureus in a Children’s Hospital in Kunming, China

Abstract

Purpose

The present study investigated the prevalence characteristics of oxacillin susceptible mecA-positive Staphylococcus aureus (OS-MRSA) in a children’s hospital in Kunming from January 2019 to December 2020.

Methods

A total of 499 S. aureus strains were included in the study and tested for oxacillin susceptibility using the VITEK 2 Compact automated antimicrobial susceptibility test system. All oxacillin-susceptible strains were detected mecA and mecC by polymerase chain reaction (PCR). E-test was used to compare the minimum inhibitory concentration (MIC) values of methicillin-susceptible S. aureus (MSSA), methicillin-resistant S. aureus (MRSA), and OS-MRSA for oxacillin, cefoxitin, penicillin, vancomycin, erythromycin, and clindamycin. Molecular typing of OS-MRSA was performed by MLST and SCCmec typing. Toxin genes were detected by PCR.

Results

Forty-five OS-MRSA strains were detected, for an overall rate of 9.02% (45/499). The MICs of MSSA, OS-MRSA, and MRSA against oxacillin were concentrated at 0.38, 0.38, and 12 μg/mL, respectively; the cefoxitin MICs of MSSA and MRSA were concentrated at 2 and 32 μg/mL respectively; and MICs of OS-MRSA were concentrated at 2 and 8 μg/mL; penicillin, vancomycin and erythromycin MICs against MSSA, OS-MRSA, and MRSA showed same centralized points and were 32, 1, and 256 μg/mL, respectively; the MICs of clindamycin against MSSA were 0.5 μg/mL, while that against OS-MRSA and MRSA were concentrated at 256 μg/mL. Molecular typing of OS-MRSA was dominated by ST59-SCCmec IV. The carrier rates of hemolysin genes (hl-a, hl-d) and fibrinogen-binding clumping factor genes (clfA, clfB) were 100% in OS-MRSA, followed by 40% (18/45) for enterotoxin genes (sea, seb).

Conclusion

OS-MRSA has a high detection rate in children, and main molecular typing is ST59-SCCmecIV in Kunming. The identification ability of automated antibacterial drug sensitivity test detection systems for OS-MRSA is very limited. A combination of phenotypic analysis and molecular detection should be used to improve OS-MRSA identification.

Keywords:

• Staphylococcus aureus
• MRSA
• OS-MRSA
• children
• oxacillin

Acknowledgments

This study was supported by the National Natural Science Foundation of China (No. 81960294, 82060291), the Basic Applied Study Planning Projects of Yunnan Province (No. 2021FB231), the Scientific Research Project of Education Department of Yunnan Province (No. 2020J0224), the Health Science and Technology Personnel Training Foundation of Kunming City of China (No. 2020-SW (reserve personnel)-109; 2021-SW (reserve personnel)-66; 2021-SW (reserve personnel)-72), the Science and Technology Planning Project of Yunnan Province (No. 2019ZF004-1-5-3).

Ethical Approval

This study was conducted in accordance with the Declaration of Helsinki. The research protocol was approved by the Ethics Committee of Kunming Children’s Hospital (reference number 2020-03-020-K01). The Ethics Committee of Kunming Children’s Hospital did not require written informed consent from patients because the data of the patients used in the study were anonymized or maintained with confidentiality.

Disclosure

The authors declare that they have no conflicts of interest for this work.