Characterization of Irreversible Electroporation Ablation with a Validated Perfused Organ Model.

PURPOSE: To develop and validate a perfused organ model for characterizing ablations for irreversible electroporation (IRE)-based therapies. MATERIALS AND METHODS: Eight excised porcine livers were mechanically perfused with a modified phosphate-buffered saline solution to maintain viability during IRE ablation. IRE pulses were delivered using 2 monopolar electrodes over a range of parameters, including voltage (1,875-3,000 V), pulse length (70-100 µsec), number of pulses (50-600), electrode exposure (1.0-2.0 cm), and electrode spacing (1.5-2.0 cm). Organs were dissected, and treatment zones were stained with triphenyl tetrazolium chloride to demonstrate viability and highlight the area of ablation. Results were compared with 17 in vivo ablations performed in canine livers and 35 previously published ablations performed in porcine livers. RESULTS: Ablation dimensions in the perfused model correlated well with corresponding in vivo ablations (R2 = 0.9098) with a 95% confidence interval of < 2.2 mm. Additionally, the validated perfused model showed that the IRE ablation zone grew logarithmically with increasing pulse numbers, showing small difference in ablation size over 200-600 pulses (3.2 mm ± 3.8 width and 5.2 mm ± 3.9 height). CONCLUSIONS: The perfused organ model provides an alternative to animal trials for investigation of IRE treatments. It may have an important role in the future development of new devices, algorithms, and techniques for this therapy.

Hypermotility in Clostridium perfringens strain SM101 is due to spontaneous mutations in genes linked to cell division.

Clostridium perfringens is a Gram-positive anaerobic pathogen of humans and animals. Although they lack flagella, C. perfringens bacteria can still migrate across surfaces using a type of gliding motility that involves the formation of filaments of bacteria lined up in an end-to-end conformation. In strain SM101, hypermotile variants are often found arising from the edges of colonies on agar plates. Hypermotile cells are longer than wild-type cells, and video microscopy of their gliding motility suggests that they form long, thin filaments that move rapidly away from a colony, analogously to swarmer cells in bacteria with flagella. To identify the cause(s) of the hypermotility phenotype, the genome sequences of normal strains and their direct hypermotile derivatives were determined and compared. Strains SM124 and SM127, hypermotile derivatives of strains SM101 and SM102, respectively, contained 10 and 6 single nucleotide polymorphisms (SNPs) relative to their parent strains. While SNPs were located in different genes in the two sets of strains, one feature in common was mutations in cell division genes, an ftsI homolog in strain SM124 (CPR_1831) and a minE homolog in strain SM127 (CPR_2104). Complementation of these mutations with wild-type copies of each gene restored the normal motility phenotype. A model explaining the principles underlying the hypermotility phenotype is presented.