Microbial contamination of clinical islet transplant preparations is associated with very low risk of infection

Background: Several published studies have analyzed microbial contamination rates of islet products, ranging from 0% to 16%. However, few studies make reference to potential clinical consequences for transplant recipients and possible impact on islet survival. Materials and Methods: The current study defines rates of microbiological contamination of islet products under current good manufacturing practice conditions in 164 patients receiving 343 transplants at a single institution. Results: Nineteen (5.5%) islet preparations showed positive microbial growth with a majority (79.4%) due to Gram-positive organisms. The most frequently identified microorganism was coagulase-negative Staphylococcus (nine of 19 [47.3%]), followed by polymicrobial organisms (eight of 19 [42.1%]). No patient developed signs of clinical infection, and there were no hepatic abscesses evident on imaging by ultrasound or magnetic resonance imaging (none of 19 [0%]), despite the use of potent T-depletional induction. Finally, we could not demonstrate any negative impact of microbiological contamination on long-term islet graft survival. Conclusions: Microbiological contamination of the final islet preparation appears to have little or no effect on patients or on islet survival when appropriate antibiotics are given. However, preparation sterility should be guaranteed at all cost in order maximize patient safety and avoid potential complications in immunosuppressed patients.