A multiphasic approach to solve 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 C. acnes was misidentified as A. vaginae. Our investigation demonstrated that the media type used to grow PC bacterial isolates can have a significant impact on the results obtained on the VITEK 2 system. Furthermore, other identification methods such as MALD-ToF and PCR amplification of the 16s RNA gene were only partially successful in the identification of C. acnes. Therefore, our findings support a multiphasic approach when PC isolates are identified as A. vaginae by the VITEK 2 system for proper identification of C. acnes using macroscopic, microscopic, and other biochemical analyses.