Cutibacterium is typically found in deep tissue culture specimens collected during revision shoulder arthroplasty. Positive cultures can be challenging to interpret clinically. A multi-institutional study that used positive control (PC) and negative control (NC) samples to assess the accuracy of Cutibacterium cultures. The link between time and cultural positive and the strength of culture positivity was investigated by researchers. Each of the 11 institutions received 12 blinded samples (10 PC and 2 NC). The ten PC samples included two sets of five different dilutions of a Cutibacterium isolate from a failed total shoulder arthroplasty with a possible periprosthetic infection. The samples were handled as if they had come straight from the surgery room at each institution. The strength of culture positivity (based on a semi-quantitative assessment), specimen development, and time to culture positivity were all recorded.

A total of 110 PC and 22 NC samples were analyzed. Cutibacterium was found in 100% of the specimens at the four greatest dilutions. In 91% of the samples, the lowest dilution proved positive. Cutibacterium was found in 14% of NC samples. Cutibacterium grew at an average rate of 4.0 ± 1.3 days in PC samples, and all grew within 7 days. Authentic positive cultures had a substantially shorter time to positivity (p<0.001) and a significantly stronger positivity (p<0.001) than fake positive cultures. This multi-institutional analysis reveals that for revision shoulder arthroplasty samples with more enormous bacterial burdens, various institutions may report highly consistent culture-positive rates. Lower bacterial loads, on the other hand, produce less reliable effects. In determining if a tissue culture sample is a true positive, clinicians might consider using a shorter time to positivity and higher strength of positivity as adjuncts.