Introduction: Renal transplant recipients are at high risk for infections due to the complexity of surgical procedure and the impact of immunosuppression. Surgical site infections (SSI) are an important cause for morbidity during the early postoperative phase. No clear recommendation exists on the role of antibiotics for prophylaxis. The main purpose of this study was to assess the most common microorganisms causing SSI after renal transplantation and evaluate their antimicrobial susceptibility to routinely used antibiotics. 
Methods: We conducted a single-centre, observational cohort study of adult patients who underwent renal transplantation in our center between January 2017 and December 2019 (n=231). The antibiotics used as prophylaxis in renal transplantation were cephalosporins. We evaluated risk factors for SSI (age, gender, body-mass index (BMI), kind of organ donation) and clinical outcome (organ function and survival, patient survival, occurrence of a SSI, duration of hospital stay). Concerning the BMI, patients were divided into three groups (group 1: <25, group 2: 25-30, group 3: >30). Microbial specimens were obtained from all patients with SSI (n=46). Isolated bacteria were identified using conventional methods and antibiotic sensitivity tests were performed. For statistical analysis, SPSS vers. 29.0 (SPSS Inc., Chicago, Illinois, USA) was used.  
Results: A total of 231 kidney transplant recipients were included (56  12.8 years, male 149, living donation 41). We identified SSIs in 46 patients (55  years, male 31, living donation 11). Patients in BMI group 1 and 2 developed a SSI in 15.4% and 18.5%, respectively, while patients in BMI group 3 showed a wound infection in 28.8%. Although the occurrence of SSI was almost twice as common in this group compared to patients with low BMI, statistical significance could not be demonstrated. The organisms (n=14), responsible for the wound infections were identified in all 46 patients with SSI. The infection was monomicrobial in 29 patients (63%) and polymicrobial in 17 patients (37%). The predominant bacteria were Staphylococcus epidermidis (23.9%), Enterococcus faecalis (21.7%) and coagulase-negative staphylococci (26.1%) as well as Candida albicans (21.7%). However, numerous other bacteria and fungi against which the routine antibiotic was not effective, were found, especially in patients with a higher BMI. As a result, the anti-infective substances were switched, but therefore effective therapy was started late.
Conclusion: SSI is an early complication after renal transplantation, which brings a great burden to patients. Therefore, preventing wound infection is extremely important. Routinely used anti-infective substances do not cover all bacteria and fungi, which especially occur in patients with a higher BMI. Therefore, the routine anti-infective therapy should be re-evaluated in further studies and possibly expanded in high-risk patients.