Contamination of single-straw carrier for vitrification

To the Editor: We read with interest the recent article by Criado et al. (1) (http://www.fertstert.org/article/S0015-0282(10)02987-0/abstract) regarding the assessment of contamination of a single-straw ultravitrification closed carrier (Ultravit). They observed no contamination in any microdrops of medium contained in the closed devices, where as the bacteria they used for forced contamination of liquid nitrogen (LN2) were present in 45% of open carriers’ strip (Cryotop).