Misidentification of Cutibacterium acnes as Atopobium vaginae during routine bacterial screening of platelet concentrates using the VITEK 2 system

Skin flora bacteria, such as Cutibacterium acnes, are the predominant contaminants of blood products used for transfusion. Platelet concentrates (PCs), a therapeutic product used to treat patients with platelet deficiencies, are stored at ambient temperature under agitation, providing ideal conditions for bacterial proliferation. PCs are screened for microbial contamination using the automated BACT/ALERT culture system. Positive cultures are processed and contaminating organisms are identified using the VITEK 2 system. Over a period of approximately 2 years, several PC isolates were identified as Atopobium vaginae to a high level of confidence. However, since A. vaginae is associated with bacterial vaginosis and is not a common PC contaminant, a retrospective investigation revealed that in all cases Cutibacterium acnes, a common PC contaminant was misidentified as A. vaginae. Our investigation revealed that the media type used to grow PC bacterial isolates can have a significant impact on the results obtained on the VITEK 2 system. Our findings support the use of macroscopic, microscopic, and other biochemical analyses to confirm the identity of unexpected species identified by the VITEK 2 system during bacterial screening of blood products.