RESUMEN
In this investigation we selected and isolated a culture derived from Salmonella enterica serovar Typhimurium SL1344 with stable increased resistance to pulsed electric fields (PEF) after repeated rounds of PEF treatment and outgrowth of survivors. The resulting culture showed a higher resistance to PEF treatments under different treatment conditions. The acquisition of PEF resistance was only observed in stationary phase cells. The cytoplasmic membrane of the resistant variant showed a higher resilience against PEF treatments, since a lower permeabilization degree was observed after PEF treatments, in comparison to the parental strain. Resistance to PEF was also accompanied by a higher tolerance to acidic pH, hydrogen peroxide and ethanol, but not to heat. The occurrence of a PEF resistant variant in S. enterica serovar Typhimurium SL1344 emphasizes the need to further study the mechanisms of inactivation and resistance by PEF for an adequate design of safe treatments.
Asunto(s)
Electricidad , Salmonella typhimurium/fisiología , Antibacterianos/farmacología , Etanol/farmacología , Calor , Peróxido de Hidrógeno/farmacología , Concentración de Iones de Hidrógeno , Salmonella typhimurium/efectos de los fármacos , Análisis de SupervivenciaRESUMEN
The ability of Staphylococcus aureus to develop stress resistance responses was investigated. Exponential growth phase cells of S. aureus CECT 4459 were exposed to sublethal conditions (acid and alkaline pH, hydrogen peroxide, and heat) and then the acquisition of resistance to acid (pH 2.5), alkali (pH 12.0), hydrogen peroxide (50mM), and heat (58 degrees C) was determined. Conditions resulting in the maximum development of homologous resistance (tolerance to the same stress), while preventing lethal effects in the population, were pH 4.5 (2h), pH 9.5 (30 min), 0.05 mM H(2)O(2) (30 min), and 45 degrees C (2h). Under these adaptation conditions, times for the first decimal reduction (TFDC) to a lethal treatment at acid pH, alkaline pH, hydrogen peroxide, and heat were increased by a factor of 1.6, 2, 2, and 6, respectively. The presence of chloramphenicol or rifampicin in the adaptation medium completely abolished the increase in homologous resistance to acid pH and to hydrogen peroxide. By contrast, the development of homologous resistance to alkaline pH resulted independently of the presence of either chloramphenicol or rifampicin. S. aureus heat resistance increased in the presence of the inhibitors during the heat shock, but only partially. In some cases, the exposure to a given stress induced cross-protection against other agents. Protective combinations of sublethal stress and lethal agents were: acid pH-heat, acid pH-hydrogen peroxide, alkaline pH-hydrogen peroxide, heat-acid pH, and heat-hydrogen peroxide. These combinations of agents applied sequentially should be avoided in food-processing environments.
Asunto(s)
Adaptación Fisiológica/fisiología , Staphylococcus aureus/fisiología , Estrés Fisiológico/fisiología , Ácidos/farmacología , Antibacterianos/farmacología , Cloranfenicol/farmacología , Manipulación de Alimentos/métodos , Calor , Peróxido de Hidrógeno/farmacología , Concentración de Iones de Hidrógeno , Rifampin/farmacología , Staphylococcus aureus/efectos de los fármacos , Factores de TiempoRESUMEN
AIMS: To study the development of resistance responses in Campylobacter jejuni to high hydrostatic pressure (HHP) treatments after the exposure to different stressful conditions that may be encountered in food-processing environments, such as acid pH, elevated temperatures and cold storage. METHODS AND RESULTS: Campylobacter jejuni cells in exponential and stationary growth phase were exposed to different sublethal stresses (acid, heat and cold shocks) prior to evaluate the development of resistance responses to HHP. For exponential-phase cells, neither of the conditions tested increased nor decreased HHP resistance of C. jejuni. For stationary-phase cells, acid and heat adaptation-sensitized C. jejuni cells to the subsequent pressure treatment. On the contrary, cold-adapted stationary-phase cells developed resistance to HHP. CONCLUSIONS: Whereas C. jejuni can be classified as a stress sensitive micro-organism, our findings have demonstrated that it can develop resistance responses under different stressing conditions. The resistance of stationary phase C. jejuni to HHP was increased after cells were exposed to cold temperatures. SIGNIFICANCE AND IMPACT OF THE STUDY: The results of this study contribute to a better knowledge of the physiology of C. jejuni and its survival to food preservation agents. Results here presented may help in the design of combined processes for food preservation based on HHP technology.
Asunto(s)
Campylobacter jejuni/fisiología , Microbiología de Alimentos , Presión Hidrostática , Ácidos/farmacología , Adaptación Fisiológica , Campylobacter jejuni/crecimiento & desarrollo , Frío , Recuento de Colonia Microbiana , Conservación de Alimentos , Calor , Concentración de Iones de Hidrógeno , Estrés FisiológicoRESUMEN
AIMS: To examine the role of the alternative general stress sigma factor sigma(B) on the resistance of Staphylococcus aureus to stresses of relevance to food preservation, with special emphasis on emerging technologies such as pulsed electric fields (PEF) and high hydrostatic pressure (HHP). METHODS AND RESULTS: S. aureus strain Newman and its isogenic DeltasigB mutant were grown to exponential and stationary growth phases and its resistance to various stresses was tested. The absence of the sigma(B) factor caused a decrease in the resistance to heat, PEF, HHP, alkali, acid and hydrogen peroxide. In the case of heat, the influence of the sigma(B) factor was particularly important, and decreases in decimal reduction time values of ninefold were observed as a result of its deficiency. The increased thermotolerance of the parental strain as compared with the sigB mutant could be attributed to a better capacity to sustain and repair sublethal damages caused by heat. CONCLUSIONS: sigma(B) factor provides S. aureus cells with resistance to multiple stresses, increasing survival to heat, PEF and HHP treatments. SIGNIFICANCE AND IMPACT OF THE STUDY: Results obtained in this work help in understanding the physiological mechanisms behind cell survival and death in food-processing environments.
Asunto(s)
Conservación de Alimentos/métodos , Factor sigma/metabolismo , Staphylococcus aureus/crecimiento & desarrollo , Staphylococcus aureus/fisiología , Recuento de Colonia Microbiana , Estimulación Eléctrica , Calor , Peróxido de Hidrógeno/farmacología , Concentración de Iones de Hidrógeno , Presión Hidrostática , Pruebas de Sensibilidad Microbiana , Estrés Oxidativo , Factor sigma/genética , Staphylococcus aureus/metabolismoRESUMEN
AIMS: To study the influence of growth temperature on the resistance of Escherichia coli to three agents of different nature: heat, pulsed electric field (PEF) and hydrogen peroxide. METHODS AND RESULTS: Escherichia coli cells were grown to stationary phase at 10 degrees C, 20 degrees C, 30 degrees C, 37 degrees C and 42 degrees C. Survival curves to a heat treatment at 57.5 degrees C, to a PEF treatment at 22 kV cm(-1) and to 40 mmol l(-1) hydrogen peroxide were obtained and fitted to a model based on the Weibull distribution to describe and compare the inactivation. Time to inactivate the first log cycle of the population at 57.5 degrees C of cells grown at 42 degrees C was sixfold higher than that corresponding to cells grown at 10 degrees C. On the contrary, cells grown at 10 degrees C and 20 degrees C were more resistant to PEF and hydrogen peroxide treatments. CONCLUSIONS: The influence of growth temperature on bacterial resistance depends on the stress applied. Cells grown at higher temperatures were more heat resistant, but more sensitive to PEF and hydrogen peroxide. SIGNIFICANCE AND IMPACT OF THE STUDY: Results obtained in this investigation help in understanding the physiology of bacterial resistance and the inactivation mechanisms of different technologies.
Asunto(s)
Escherichia coli/crecimiento & desarrollo , Microbiología de Alimentos , Calor , Recuento de Colonia Microbiana , Desinfectantes/farmacología , Electricidad , Escherichia coli/efectos de los fármacos , Peróxido de Hidrógeno/farmacología , Concentración de Iones de Hidrógeno , Pruebas de Sensibilidad MicrobianaRESUMEN
The survival of four enterotoxigenic strains of Staphylococcus aureus (with different pigment content) to heat and to pulsed electric fields (PEF) treatments, and the increase in resistance to both processing stresses associated with entrance into stationary phase was examined. Survival curves to heat (58 degrees C) and to PEF (26 kV/cm) of cells in the stationary and in the exponential phase of growth were obtained. Whereas a wide variation in resistance to heat treatments was detected amongst the four strains, with decimal reduction time values at 58 degrees C (D(58 degrees C)) ranging from 0.93 to 0.20 min, the resistance to PEF was very similar. The occurrence of a higher tolerance to heat in stationary phase was coincident with a higher content in carotenoid pigmentation in S. aureus colonies. However, cells of the most heat resistant (pigmented) and the most heat sensitive (non-pigmented) strains in the mid-exponential phase of growth showed similar resistance to heat and to PEF. Therefore the increase in thermotolerance upon entrance into stationary phase of growth was more marked for the pigmented strains. Recovery in anaerobic conditions particularly enhanced survival to heat treatments in a non-pigmented strain. Strain CECT 4630, which possess a deficient sigma B activity, showed low heat resistance, low pigmentation, and reduced increase in thermotolerance in stationary phase. These results indicate that the magnitude of the development of a higher heat resistance in S. aureus in stationary phase is positively related to the carotenoid content of the strain. The development of tolerance to pulsed electric field was less relevant and not linked to the carotenoid content.