The gram-positive non-spore-forming anaerobic rods most frequently recovered from blood cultures as a contaminant are:

Propionibacterium acnes is a gram-positive, non-spore-forming anaerobic rod widely recognized as a skin commensal that can be found in blood cultures, especially when contamination occurs. It is often associated with the skin flora, which means that during venipuncture, it can inadvertently enter the bloodstream, leading to positive blood cultures that may be interpreted as contamination rather than true infection, particularly if clinical signs of infection are absent.

This organism is best known for its role in conditions such as acne, but its presence in blood cultures is significant because it highlights how skin bacteria can be mistaken for pathogens. The other options, such as Clostridium perfringens, are spore-formers and are more typically linked to serious infections rather than as common contaminants. Staphylococcus intermedius, although it can be clinically significant, is not as frequently described in blood cultures as a contaminant in the same context as Propionibacterium acnes. Veillonella parvula is a member of the normal flora in the oral cavity and gastrointestinal tract and does appear in blood cultures, but it is less commonly encountered as a contaminant compared to Propionibacterium acnes.

Collectively, this background