There were 178 PJI and 82 aseptic failure (AF) cases analyzed,
yielding
770 organisms (median, 3/subject;
range, 1–19/subject). MALDI-TOF MS was employed for the identification of 455 organisms (59%) in 197 subjects
(123 PJIs and 74 AFs), with 89% identified to the species level using this technique. Gram-positive bacteria
accounted for 68% and 93% of isolates in PJI and AF, respectively. However, the profile of species associated
with infection compared to specimen contamination differed. Staphylococcus aureus and Staphylococcus caprae
were always associated with infection, Staphylococcus epidermidis and Staphylococcus lugdunensis were equally
likely to be a pathogen or a contaminant,
whereas the other coagulase-negative staphylococci were more frequently
contaminants.
Most streptococcal and Corynebacterium isolates were pathogens. The likelihood that an
organism was a pathogen or contaminant differed with the prosthetic joint location, particularly in the case of
Propionibacterium acnes. MALDI-TOF MS is a valuable tool for the identification of bacteria isolated from patients
with prosthetic joints, providing species-level identification that may inform culture interpretation of pathogens
versus contaminants.