To Örebro University

BACKGROUND: Sternal wound infections (SWI) and aortic graft infections (AGI) are serious complications after cardiac surgery. Staphylococcus aureus and coagulase-negative staphylococci are the most common causes of SWI, while AGI are less studied. AGI may occur from contamination during surgery or postoperative haematogenous spread. Skin commensals, such as Cutibacterium acnes, are present in the surgical wound; however, their ability to cause infection is debated.

AIM: The aim of this study was to investigate the presence of skin bacteria in the sternal wound and to evaluate their possible ability to contaminate surgical materials.

METHODS: We included 50 patients that underwent coronary artery bypass graft surgery and/or valve replacement surgery at our centre from 2020 to 2021. Cultures were collected from skin and subcutaneous tissue at two time points during surgery, and from pieces of vascular graft and felt that were pressed against subcutaneous tissue. The most common bacterial isolates were tested for antibiotic susceptibility with disk diffusion and gradient tests.

FINDINGS: Cultures from skin had bacterial growth in 48% of patients at surgery start and in 78% after two hours, and cultures from subcutaneous tissue were positive in 72% and 76% of patients, respectively. The most common isolates were C. acnes and S. epidermidis. Cultures from surgical materials were positive in 80-88%. No difference in susceptibility was found for S. epidermidis isolates at surgery start compared to after two hours.

CONCLUSIONS: The results suggest that skin bacteria are present in the wound and may contaminate surgical graft material during cardiac surgery.