Influence of tonicity and chloramphenicol on hyperthermic cytotoxicity and cell permeability under various heating rates

Abstract

The cell lethality and permeability induced in Escherichia coli B/r, Escherichia coli Bs-1 and Zygosaccharomyces bailii cells by high temperature (52 degrees C) after heating at different rates (mean s 0.015, 0.25 and 1.50 degrees C per s) and in media of different tonicity and content (isotonic YEP broth versus 0.01 M phosphate buffer, pH 7.0 containing different concentrations of NaCl) and with versus without chloramphenicol (10 micrograms/ml) have been investigated. Hyperthermic treatment in YEP broth of isotonic 0.01 M phosphate buffer resulted in markedly reduced cytotoxicity with decreasing heat rate. The heating rate effect was larger when the cells were treated in YEP broth. Chloramphenicol, which is known to inhibit expression of heat shock proteins in bacteria, did not affect the viability of cells or the development of thermotolerance in cells heated at different heating rates in isotonic phosphate buffer but prevented the development of an additional degree of thermotolerance in cells heated slowly in YEP broth. In contrast, the differential effect of heating rate on cytotoxicity and cell permeability was not demonstrated when cells were heated in hypertonic solution (1M NaCl in phosphate buffer, pH 7.0). It is proposed that heat destabilization of the osmotic cell homeostasis, which is more profound after rapid heating, plays a major part in heat induced cellular lethality.

Responses ofSaccharomyces cerevisiae to thermal stress

“…Because the presence of cycloheximide did not affect the heat slope-induced thermotolerance, it could be proposed that cytoplasmic protein synthesis and more particularly Hsps were not involved in this type of thermal resistance. Similar results were found by Morozov et al (1997) who showed that chloramphenicol, which inhibits protein synthesis, had little effect on the development of thermotolerance in Escherichia coli cells slowly heated in nutrient medium.…”

“…The major components of cells, such as proteins and plasma membrane, are dramatically affected if cells are exposed to elevated temperatures . Nevertheless, under defined conditions most eukaryotic (Mager and Moradas Ferreira, 1993) and prokaryotic (Morozov et al, 1997) microorganisms are able to acquire a certain degree of thermotolerance, so as to protect their components. For yeasts, exposure to a mild preconditioning heat treatment leads them to acquire a certain degree of thermotolerance, which is related to heat shock factor and stress response element pathways (Mager and Moradas Ferreira, 1993;Morano et al, 1998;Parsell et al, 1994).…”

Surviving the heat: heterogeneity of response in Saccharomyces cerevisiae provides insight into thermal damage to the membrane

“…Previous publications (Gervais and Martínez de Marañón, 1995 ; Morozov et al ., 1999 ; Marechal et al ., 1999 ; Martinez de Marañon et al ., 1999 ) concerning strain CBS1171 demonstrated the consequences of heat slope and shock on the reduction in colony-forming units. More recently, Guyot and colleagues ( 2005 ) showed that the heat-slope-induced thermal resistance could be eliminated by a rapid cooling from 50°C to 25°C, meaning that reversible and thermally dependent mechanisms were related to this type of resistance.…”

High Heating Rates Affect Greatly the Inactivation Rate of Escherichia coli

“…Some bacterial genera became more heat resistant under high heating rates. For example, Hassani et al ( 2006 ) showed that S. aureus exhibited higher thermal resistance at higher heating rates (up to 9°C/min), while others turned out to be more resistant at slow heating rates (Humphrey et al, 1993 ; Stephens et al, 1994 ; Morozov et al, 1997 ; Hassani et al, 2005 ; Valdramidis et al, 2006 ; Hassani et al, 2007 ). Also, Mañas et al ( 2003 ) found no influence of the heating rate (between 0.5 and 4°C/min) on the thermal resistance of Salmonella Senftenberg 775 W, which, on the other hand, is an exceptionally heat resistant strain.…”