Effects of tissue, time and temperature on decontamination efficacy of Base.128

Introduction: Decontamination is a crucial step in allograft processing. Tissue banks have established their own decontamination procedures using different solutions, depending on tissue, as well as different time and temperature conditions, which often require a complex validation process.

Purpose: To investigate the decontamination efficacy of the industrially manufactured medical device BASE.128 both in vitro and in the presence of artificially contaminated tissues.

Methods: In vitro time-kill studies: BASE.128, containing three different antibiotics, was inoculated with 108 CFU/device of reference microorganisms according to Pharmacopoeia: Staphylococcus Aureus, Candida Albicans, Pseudomonas Aeruginosa, and an additional bacterial strain: methicillin-resistant Staphylococcus Epidermidis. Media were incubated at 4°C, 22°C and 37°C. Microbial content was quantified after 3h, 6h, 12h, and 24h of incubation at all three temperatures by membrane filtration sterility test.

Contaminated tissues: Sterile pig heart valve, bone and skin were superficially contaminated with 106 – 105 CFU/tissue of the selected microorganisms. Tissues were then immersed in BASE.128 for 6h at 37°C or 24h at 4°C. After decontamination, tissue samples were transferred to Trypton Soy Broth containing a mixture of antibiotic-neutralizing resins. Samples were stirred for 1 h for an effective antibiotic neutralization and then incubated at 37°C for 14 days for microbiological analysis. Elimination of antibiotics was checked by agar diffusion test, immediately after antibiotic neutralization. Tissue decontamination was examined both qualitatively by visual inspection of media for turbidity for up to 14 days and quantitatively by plating sample media on Petri dishes.

Results: In vitro studies showed that a minimum decontamination efficacy of 6, 5 and 4 logs was achieved after 12 h incubation in BASE.128 at 37°C, 22°C and 4°C, respectively. Time-kill curves of the investigated microorganisms showed that the decrease in incubation temperature delays the decontamination effects and reduces it of 1 log at 4°C.
Artificial contamination of heart valve, bone or skin, and subsequent decontamination in BASE.128 showed that the presence of the tissue does not affect the decontamination efficacy of BASE.128. Based on our qualitative and quantitative results, an average decrease of 5 logs was observed for all investigated microorganisms in all examined tissues at both decontamination conditions. The agar diffusion test showed the absence of bacterial growth inhibition, thus indicating the absence of residual antibiotic activity.

Conclusions: Our results show that the medical device BASE.128 eliminates effectively all the investigated microorganisms from tissues with high decontamination efficacy. The time-kill studies demonstrate the relevance of time and temperature for tissue decontamination. Conversely, the presence of tissue does not affect the decontamination efficacy of BASE.128. In conclusion, BASE.128 is a validated decontamination medium for different tissues, which fits the standard decontaminating procedures of Tissue Banks.