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McCormack, Michael

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McCormack

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Michael

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McCormack, Michael
Author's Publications: search.filters.isAuthorOfPublication.64028d20-feb2-4495-9b48-7992342f5290

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    Eradication of Multidrug-Resistant Pseudomonas Biofilm With Pulsed Electric Fields
    (Wiley, 2015-09-09) Khan, Saiqa I.; Blumrosen, Gaddi; Vecchio, Daniela; Golberg, Alexander; Hamblin, Michael; McCormack, Michael; Yarmush, Martin; Austen, William
    Biofilm formation is a significant problem, accounting for over eighty percent of microbial infections in the body. Biofilm eradication is problematic due to increased resistance to antibiotics and antimicrobials as compared to planktonic cells. The purpose of this study was to investigate the effect of Pulsed Electric Fields (PEF) on biofilm-infected mesh. Prolene mesh was infected with bioluminescent Pseudomonas aeruginosa and treated with PEF using a concentric electrode system to derive, in a single experiment, the critical electric field strength needed to kill bacteria. The effect of the electric field strength and the number of pulses (with a fixed pulse length duration and frequency) on bacterial eradication was investigated. For all experiments, biofilm formation and disruption were confirmed with bioluminescent imaging and Scanning Electron Microscopy (SEM). Computation and statistical methods were used to analyze treatment efficiency and to compare it to existing theoretical models. In all experiments 1500V are applied through a central electrode, with pulse duration of 50s, and pulse delivery frequency of 2Hz. We found that the critical electric field strength (Ecr) needed to eradicate 100-80% of bacteria in the treated area was 121 +/- 14V/mm when 300 pulses were applied, and 235 +/- 6.1V/mm when 150 pulses were applied. The area at which 100-80% of bacteria were eradicated was 50.5 +/- 9.9mm(2) for 300 pulses, and 13.4 +/- 0.65mm(2) for 150 pulses. 80% threshold eradication was not achieved with 100 pulses. The results indicate that increased efficacy of treatment is due to increased number of pulses delivered. In addition, we that showed the bacterial death rate as a function of the electrical field follows the statistical Weibull model for 150 and 300pulses. We hypothesize that in the clinical setting, combining systemic antibacterial therapy with PEF will yield a synergistic effect leading to improved eradication of mesh infections.
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    Photochemical Tissue Passivation Reduces Vein Graft Intimal Hyperplasia in a Swine Model of Arteriovenous Bypass Grafting
    (John Wiley and Sons Inc., 2016) Goldstone, Robert N.; McCormack, Michael; Khan, S; Salinas, Harry M.; Meppelink, Amanda; Randolph, Mark; Watkins, Michael; Redmond, Robert; Austen, William
    Background: Bypass grafting remains the standard of care for coronary artery disease and severe lower extremity ischemia. Efficacy is limited by poor long‐term venous graft patency secondary to intimal hyperplasia (IH) caused by venous injury upon exposure to arterial pressure. We investigate whether photochemical tissue passivation (PTP) treatment of vein grafts modulates smooth muscle cell (SMC) proliferation and migration, and inhibits development of IH. Methods and Results: PTP was performed at increasing fluences up to 120 J/cm2 on porcine veins. Tensiometry performed to assess vessel elasticity/stiffness showed increased stiffness with increasing fluence until plateauing at 90 J/cm2 (median, interquartile range [IQR]). At 90 J/cm2, PTP‐treated vessels had a 10‐fold greater Young's modulus than untreated controls (954 [IQR, 2217] vs 99 kPa [IQR, 63]; P=0.03). Each pig received a PTP‐treated and untreated carotid artery venous interposition graft. At 4‐weeks, intimal/medial areas were assessed. PTP reduced the degree of IH by 66% and medial hypertrophy by 49%. Intimal area was 3.91 (IQR, 1.2) and 1.3 mm2 (IQR, 0.97; P≤0.001) in untreated and PTP‐treated grafts, respectively. Medial area was 9.2 (IQR, 3.2) and 4.7 mm2 (IQR, 2.0; P≤0.001) in untreated and PTP‐treated grafts, respectively. Immunohistochemistry was performed to assess alpha‐smooth muscle actin (SMA) and proliferating cell nuclear antigen (PCNA). Objectively, there were less SMA‐positive cells within the intima/media of PTP‐treated vessels than controls. There was an increase in PCNA‐positive cells within control vein grafts (18% [IQR, 5.3]) versus PTP‐treated vein grafts (5% [IQR, 0.9]; P=0.02). Conclusions: By strengthening vein grafts, PTP decreases SMC proliferation and migration, thereby reducing IH.