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Appl Environ Microbiol. 1975 May; 29(5): 685-691
Copyright © 1975 American Society for Microbiology. All Rights Reserved.

Effect of Dichlorodifluoromethane on the Appearance, Viability, and Integrity of Escherichia coli

Departments of Food Science^* and Bacteriology, University of Wisconsin-Madison, Madison, Wisconsin 53706

ABSTRACT

Cultures of Escherichia coli H52 were treated with liquid dichlorodifluoromethane (fluorocarbon-12 [f-12]) for 2 h at 22 C and then examined microscopically. Treated cells tended to clump, and their cytoplasms were generally less dense and less uniform in appearance than those of control cells. E. coli ML30 was exposed to f-12 at a concentration of 1.25 x saturation for times up to 1,200 min at 22 C. Cells were examined for changes in viability (plate count), permeability (as measured by exit of -[¹⁴C]methylglucoside or uptake of o-nitrophenyl-ß-D-galactopyranoside), release of compounds absorbing at 260 nm, and lysis (changes in absorbance at 420 nm). Large losses of -methylglucoside and of percentage of viability occurred after brief exposure to f-12. Release of compounds absorbing at 260 nm occurred more slowly than the aforementioned events, possibly because these molecules are larger than -methylglucoside. During 1,200-min exposure to f-12, the number of survivors decreased from 10⁹ to 10⁴ organisms/ml, the loss of compounds absorbing at 260 nm amounted to 50% and 32% lysis occurred. Most of these changes occurred during the first 300 min of treatment. Loss of -methylglucoside was almost complete after 1-min exposure to f-12. These results suggest that death of the cell involves several stages, with a change of permeability occurring first, followed by leakage of compounds of increasing size and, finally, lysis.

¹ Present address: Department of Microbiology, University of the Orange Free State, P.O. Box 339, Bloemfontein 9300, South Africa.