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A Microbiologic Comparison of Acellular Dermal Matrices as an Aseptic Reconstructive Material and a Scaffold for Stem Cell In-growth
Shaun D. Mendenhall, MD1, Tim H.F. Daugherty, MS1, Nicole M. Cosenza, MS1, Katherine E. McKenna, MD1, Ryan W. Schmucker, MD1, Joel D. Reichensperger, BS1, Ashim Gupta, PhD1, Janak Koirala, MD, MPH1, Paul S. Cederna, MD2, Michael W. Neumeister, MD1.
1Southern Illinois University School of Medicine, Springfield, IL, USA, 2University of Michigan School of Medicine, Ann Arbor, MI, USA.
Over the last 10 years, the use of acellular dermal matrix (ADM) in breast surgery has gained popularity. Recent meta-analyses demonstrate an increased risk of infection when ADM is used for breast reconstruction. This may be due to the fact that some ADMs are actually not terminally sterilized, but are “aseptically processed.” Further studies suggest that sterile ADMs may have a lower infection risk, however terminal sterilization processes may alter ADM architecture and negatively influence tissue in-growth. The present study evaluates sterile and non-sterile ADMs for evidence of bacterial contamination and whether or not terminal sterilization affects tissue architecture and stem cell in-growth.
Five separate 2x4cm samples of 14 different brands of ADM were sterilely cut into 1x1 cm pieces, fixed, paraffin embedded, mounted on slides, and used for fluorescent in-situ hybridization (FISH) using a universal bacterial DNA probe EUB338 to detect presence of bacterial DNA on ADMs. Separate samples were placed in liquid culture media for aerobic/anaerobic bacteria, acid-fast bacilli (AFB), and fungi. Standard culture media was incubated for 3 weeks and AFB for 6 weeks. The Biomerieux Vitek-2 system was used to identify organisms from positive cultures. Separate ADM samples were seeded with human adipose derived stem cells (ADSCs), incubated for two weeks, and evaluated with confocal microscopy to quantify the number of ADSCs per high power field (HPF). Scanning electron microscopy (SEM) was performed to evaluate ADM nano-architecture. Differences were tested with the Mann-Whitney U test with p<0.05 considered significant.
Results of FISH demonstrated traces of bacterial DNA on all matrices. There were more bacteria per HPF in the aseptically processed group compared to the sterile group (3.6 vs. 1.6, p= 0.0003). However, the number of positive cultures was similar between groups (sterile=4, vs. non-sterile=3, only 1-2 colonies each). Stem cell seeding/culturing demonstrated a wide variation of stem cell in-growth between matrices ranging from 2-136 ADSCs/HPF with no difference between sterile/non-sterile groups (64 vs. 79, p=0.2). SEM demonstrated marked differences in collagen organization between groups.
FISH analysis demonstrated more evidence of prior bacterial contamination on non-sterile ADMs. However, standard culture techniques of both sterile and aseptically processed ADMs yielded an equal amount of positive cultures, all of which were standard skin flora and likely contaminants from the culture process. Although there were marked differences in ADSC in-growth between matrices, there was no difference between groups based on sterility. Sterile ADMs had more disorganized collagen structure than non-terminally sterilized ADMs, likely due to the sterilization process. Based on these findings, aseptic processing of ADMs is likely sufficient to prevent clinically-relevant contamination of ADMs and although terminal sterilization does not affect stem cell in-growth, it may come at the cost of damaging the collagen network.
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