Bacteriostasis testing on allograft tissue inoculated in Wilkins-Chalgren broth

Tissue banks culture tissue specimens to confirm the absence of viable micro-organisms after decontamination with antibiotics. It is possible that antibiotic residues attached to decontaminated tissue are introduced into enrichment culture media. These could have an inhibitory effect on the culture results and generate false-negative results. Our aim was to detect bacteriostasis in Wilkins-Chalgren broth inoculated with bone and tendon remnants. These remnants had been soaked in a solution containing gentamicin as part of the tissue-processing procedure. We used the United States Pharmacopeia method for bacteriostasis testing with gentamicin-susceptible Pseudomonas aeruginosa American Type Culture Collection (ATCC) 15442, Staphylococcus aureus ATCC 6538, Bacillus subtilis ATCC 6633 as test strains, and gentamicin-resistant Candida albicans ATCC 90029 as control. The residual gentamicin concentration in the broths was determined and gentamicin-soaked tissue was placed on Mueller-Hinton agar inoculated with a staphylococcal suspension. Bacteriostasis was present in 53-75% of the reference test strains. Tendon remnants had a significantly higher rate of bacteriostasis (85%) than bone remnants (28%). Broths inoculated with tendon remnants had the highest residual gentamicin concentrations.