Letter to the Editor Ice from an ice machine is a potential source of bacterial contamination for HPC products - implications for cell-processing facilities

Cryopreservation of hematopoietic grafts with DMSO is a standard method of long-term storage of HPC p]. As DMSO releases heat after it is added to the media, the freezing solution has to be cooled before being added to the cell product. Until 1997, we routinely used wet ice made by an ice machine for cooling the DMSO-medium solution. The freezing solution was then connected to the product bag using aseptic spiking devices, and the DMSO­ medium was transferred into the storage bag containing the HPCs. During 1997, we observed a considerable number of cases of bacterial contamination in HPC products obtained after addition of the freezing solution to the cell product (29% positive cultures). The spectrum of microorganisms detected included a high number of waterborne bacteria, e.g., Sphingomonas paucimobilis or Comamonas acidovorans. Review of the cryopreservation process identified the ice produced by the ice machine as the most likely source of this contamination. Bacteriological analysis of the ice revealed the presence of the same microorganisms as those detected in the contaminated HPC products. We changed our cooling method and now use reusable cooling pads for refrigeration of the DMSO-medium solution (Mergo GmbH, Wesel, Germany). This intervention resulted in a marked reduction in the contamination rate of HPC products to < 2% during the following years (1998-2002). The spectrum of microorganisms observed also changed, from waterborne bacteria to skin-derived bacteria.