Abstract: Objective To compare the survival of Staphylococcus epidermidis in whole blood, red blood cell suspensions, and platelet concentrates, and to preliminarily investigate biofilm formation on the inner wall of blood storage bags. Methods Whole blood was collected from five healthy volunteers, and red blood cell suspensions and platelet concentrates were manually prepared. Skin flora from the antecubital region was sampled using sterile swabs, and the predominant isolate was identified as S. epidermidis. Each blood component was spiked with the bacterial suspension to a final concentration of approximately 10 CFU/mL, with sterile controls set up in parallel. Whole blood and red blood cell suspensions were stored at 4 ℃, while platelet concentrates were agitated at (22±2) ℃. Samples were taken on days 1 (within 2 h), 3, 5, 7, and 9 post-inoculation, plated on blood agar, and colonies were counted after 48 h of incubation. At the end of the experiment, crystal violet staining was used to assess biofilm formation on the inner bag surface. Results On day 1, all three groups yielded small numbers of bacteria (1~8 CFU/100 μL), with no significant difference among groups (H=1.792, P=0.436). Thereafter, the three groups showed distinctly different trends: in the whole-blood group, bacteria were progressively cleared from day 3 onward, with 4 of 5 specimens becoming sterile by day 9 and the remaining one showing only 1 CFU/100 μL. In the red blood cell suspension group, counts rose to 19 (8, 32) CFU/100 μL on day 3, but by day 9, 3 specimens were sterile. In the platelet concentrate group, massive proliferation occurred as early as day 3, with counts reaching 81 (33 300) CFU/100 μL, and all specimens became uncountable from day 7 onward. Crystal violet staining revealed purple coloration on the inner bag walls in both the whole-blood and red blood cell suspension groups, including bags that had become sterile. Conclusion Whole blood and red blood cell suspensions exhibit a certain capacity for self-clearance against S. epidermidis, whereas platelet concentrates strongly support bacterial proliferation. Bacteria may form biofilms on the inner bag surface, potentially leading to false-negative results in routine culture and detection.

Key words: Staphylococcus epidermidis, Whole blood, Red blood cell suspension, Platelet concentrate, Bacterial contamination, Biofilm, Transfusion safety