600-ns Pulsed Electric Fields Affect Inactivation and Antibiotic Susceptibilities of Escherichia coli and Lactobacillus acidophilus
Journal Article - Open Access
AIR FORCE RESEARCH LAB FORT SAM HOUSTON TX HUMAN PERFORMANCE WING (711TH) FORT SAM HOUSTON United States
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Cell suspensions of Escherichia coli and Lactobacillus acidophilus were exposed to 600-ns pulsed electric fieldsnsPEFs at varying amplitudes Low-13.5, Mid-18.5 or High-23.5 kV cm1 and pulse numbers 0 sham, 1, 5, 10,100 or 1000 at a 1 hertz Hz repetition rate. The induced temperature rise generated at these exposure parameters, hereafter termed thermal gradient, was measured and applied independently to cell suspensions in order to differentiate inactivation triggered by electric field E-field from heating. Treated cell suspensions were plated and cellular inactivation was quantified by colony counts after a 24-hour h incubation period. Additionally, cells from both exposure conditions were incubated with various antibiotic-soaked discs to determine if nsPEF exposure would induce changes in antibiotic susceptibility. Results indicate that, for both species, the total delivered energy amplitude, pulse number and pulse duration determined the magnitude of cell inactivation. Specifically, for 18.5 and 23.5 kV cm1exposures, L.acidophilus was more sensitive to the inactivation effects of nsPEF than E. coli, however, for the 13.5 kVcm1 exposures E. coli was more sensitive, suggesting that L. acidophilus may need to meet an E-field threshold before significant inactivation can occur. Results also indicate that antibiotic susceptibility was enhanced by multiple nsPEF exposures, as observed by increased zones of growth inhibition. Moreover, for both species, a temperature increase of 20 C 89 of exposures was not sufficient to significantly alter cell inactivation, whereas none of the thermal equivalent exposures were sufficient to change antibiotic susceptibility categories.