Abstract
Protocols for processing of tissue from arthroplasty infections vary and might affect the recovery of bacteria. We compared homogenization, bead beating and enzymatic disruption for recovery of live bacteria from tissue samples.
Suspensions of Staphylococcus aureus and Escherichia coli were prepared as controls. Three samples were taken from each and the first was bead beaten, the second homogenized, and Proteinase K was added for 10 and 30 minutes to the third sample before culturing. In addition, artificially inoculated pork tissue and known infected human tissue samples were processed by either homogenization or bead beating prior to cultures and results were compared.
Number of cycles of bead beating and homogenization and duration of Proteinase K treatment had significant effects. Bead beating for 2 and 4 cycles reduced the yield of S.aureus to 52% and 20% of control, and E.coli to 33% and 8%. Homogenization for 2 and 4 cycles reduced S.aureus to 86% and 65% of control, and E.coli to 90% and 87%. Proteinase K for 10 minutes and 30 minutes reduced the yield of S.aureus to 75% and 33% of control, and E.coli to 91% and 49% respectively. Inoculated Pork tissue showed a reduction in S.aureus recovery of 90% for bead beating compared to homogenization, and 80% in the case of E.coli. Bead beating of infected human tissue samples reduced the yield by 58% compared to homogenization.
Bead-beating is a common recommended method of processing tissue from arthroplasty cases. However, even though it produces a homogeneous sample, it does so at the cost of significant loss of viable bacteria. Homogenization and 10 minutes of Proteinase K incubation are almost equivalent, but the homogenizer is preferred being more controllable and cheaper. This should help to define guidelines for diagnosing infections using tissue samples.
