Effect of cell immobilization on heat-induced sublethal injury of Escherichia coli, Salmonella Typhimurium and Listeria innocua

Noriega, Estefanía; Velliou, Eirini; Derlinden, Eva Van; Mertens, Laurence; Impe, Jan Van

doi:10.1016/j.fm.2013.06.015

Cited by 51 publications

(49 citation statements)

References 86 publications

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“…Therefore, the more severely injured cells are, the lower the NaCl concentration required to prevent their growth – which fits perfectly with the previously stated hypothesis of the coexistence of different levels of damage, from minor to eventually lethal (Wesche et al, 2009; Noriega et al, 2013). …”

Section: Resultssupporting

confidence: 89%

“…Moreover, previous results have demonstrated that the presence of betaine in the recovery medium can compensate for defective phenotypes in their osmoregulatory systems (Cebrián et al, 2015). However, the evaluation of the occurrence of sublethal injury incurred in E. coli after inimical treatments via SMPT usually employs complete and nutritionally rich agar media (such as tryptic soy yeast extract agar [TSAYE] or plate count agar) as the non-selective medium (Wuytack et al, 2002; Noriega et al, 2013). In contrast with the controlled and osmoprotectant-free composition of the M9 agar medium, TSAYE contains the osmoprotectant betaine (Dulaney et al, 1968).…”

Section: Resultsmentioning

confidence: 99%

“…Tryptic soy agar (Biolife, Milan, Italy) plus 0.6% of yeast extract (Biolife; TSAYE) was selected as the rich recovery medium, given its widespread use in the enumeration of bacterial injury (Miller et al, 2006; Noriega et al, 2013). Preliminary experiments showed that recovery in M9 minimal agar medium after different thermal treatments yielded similar counts than in TSAYE (data not shown).…”

Section: Methodsmentioning

confidence: 99%

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Detection of Thermal Sublethal Injury in Escherichia coli via the Selective Medium Plating Technique: Mechanisms and Improvements

2016

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In food preservation, the synergistic combination of different technologies aims to maximize the total lethality of the process and minimize the intensity of each hurdle. This is especially the case when at least one of the treatments can cause sublethal (reparable) injury in a great proportion of the population, so that sublethally injured cells can end up being entirely inactivated by the other hurdle(s). The selective medium plating technique (SMPT) is extensively used to enumerate bacterial sublethal injury after inimical treatments, being sodium chloride added to the recovery medium to detect damaged bacterial envelopes. However, little work has been done to explain the reasons for the inability of sublethally injured cells to outgrow in selective agar media, whereas they are able to grow in non-selective agar. In the present paper, the performance of SMPT on Escherichia coli cells after heat treatments is explored by applying different selective agents in the recovery media, using mutants lacking factors involved in osmoregulation, and also by examining the integrity of the cytoplasmic membrane. In view of the results, the possibility of a specific toxic effect of Na+ as the main mechanism under SMPT was discarded, since the same level of sublethal injury was detected using KCl instead of NaCl. The synthesis of the osmoprotectant trehalose determined the maximum osmotolerance of intact cells to the selective agents, but was not crucial in the quantification of sublethal injury. Moreover, for the first time, the extent of sublethal injury detected via SMPT was directly correlated with the physical loss of integrity of the cell membrane in 99.999% of the initial population. This was achieved through statistical analysis of flow cytometry data using propidium iodide-exclusion technique when that dye was added before thermal treatments. The present work confirms the adequacy of SMPT as a tool for detecting the occurrence and quantity of sublethally injured cells after thermal treatments and thus, for efficiently designing the combination of heat with other preservation techniques. We also propose the study of statistical analysis from flow cytometry data for a more rapid quantification of bacterial sublethal injury in a broad detection range.

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Section: Resultssupporting

confidence: 89%

Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

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Detection of Thermal Sublethal Injury in Escherichia coli via the Selective Medium Plating Technique: Mechanisms and Improvements

2016

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“…A solid environment causes an additional stress to colonies, ultimately resulting in slower growth and a confinement of the growth domain compared to the liquid systems (Noriega et al, 2010b;Theys et al, 2008;Wilson et al, 2002). Additionally, the solid matrix causes changes in metabolism, cell development, morphology, membrane permeability, surface tension, and osmotic pressure, and affects cell variability and physiological state (Dervakos and Webb, 1991;Meldrum et al, 2003;Noriega et al, 2013;Wilson et al, 2002).…”

Section: Introductionmentioning

confidence: 99%

Effect of cell immobilization on the growth dynamics of Salmonella Typhimurium and Escherichia coli at suboptimal temperatures

Smet

Derlinden

Mertens

et al. 2015

International Journal of Food Microbiology

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Predictive microbiology has recently acknowledged the impact of the solid(like) food structure on microbial behavior. The presence of this solid(like) structure causes microorganisms to grow as colonies and no longer planktonically as in liquid. In this paper, the growth dynamics of Salmonella Typhimurium and Escherichia coli were studied as a function of temperature, considering different growth morphologies, i.e., (i) planktonic cells, (ii) immersed colonies and (iii) surface colonies. For all three growth morphologies, both microorganisms were grown in petri dishes. While E. coli was grown under optimal pH and water activity (aw), for S. Typhimurium pH and aw were adapted to 5.5 and 0.990. In order to mimic a solid(like) environment, 5% (w/v) gelatin was added. All petri dishes were incubated under static conditions at temperatures in the range [8.0°C-22.0°C]. Cell density was determined via viable plate counting. This work demonstrates that the growth morphology (planktonic vs. colony) has a negligible effect on the growth dynamics as a function of temperature. The observation of almost equal growth rates for planktonic cultures and colonies is in contrast to literature where, mostly, a difference is observed, i.e., μplanktonic cells≥μimmersed colonies≥μsurface colonies. This difference might be due to shaking of the liquid culture in these studies, which results in a nutrient and oxygen rich environment, in contrast to the diffusion-limited gel system. Experiments also indicate that lag phases for solid(like) systems are similar to those for the planktonic cultures, as can be found in literature for similar growth conditions. Considering the maximum cell density, no clear trend was deducted for either of the microorganisms. This study indicates that the growth parameters in the suboptimal temperature range do not depend on the growth morphology. For the considered experimental conditions, models previously developed for liquid environments can be used for solid(like) systems.

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“…Therefore, the tail in the survivor curves may be attributed to a subpopulation of more resistant bacteria 647 that decline at a slower rate than the majority of cells (Juneja et al, 1997). These heat resistance patterns have already been reported for E. coli serotypes (Cornet et al, 2011;Velliou et al, 2011;Noriega et al, 2013). Van Derlinden et al (2011) hypothesized that one subpopulation is able to overcome the environmental stress, whereas a second is unable to resist stress and hence is destroyed.…”

Section: Discussionmentioning

confidence: 73%

Thermal inactivation kinetics of Shiga toxin-producing Escherichia coli in buffalo Mozzarella curd

Trevisani

Mancusi

Valero

2014

Journal of Dairy Science

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The use of raw milk in the processing of buffalo Mozzarella cheese is permitted, but the heat treatment used for stretching the curd must ensure that the final product does not contain pathogens such as Shiga toxin-producing Escherichia coli (STEC) that may be present on buffalo dairy farms. This study carried out challenge tests at temperatures between 68 °C and 80 °C for 2 to 10 min to simulate curd temperatures during the stretching phase. Curd samples were inoculated with 2 STEC strains (serotypes O157 and O26), and their inactivation rates were assessed in the different challenge tests. The curd samples were digested with papain to ensure a homogeneous dispersion of bacteria. The STEC cells were counted after inoculation (range 7.1-8.7 log cfu/g) and after heat treatments using the most probable number (MPN) technique. A plot of log MPN/g versus time was created for each separate experiment. The log linear model with tail was used to provide a reasonable fit to observed data. Maximum inactivation rate (k(max), min(-1)), residual population (log MPN/g), decimal reduction time (min), and time for a 4D (4-log10) reduction (min) were estimated at each temperature tested. A 4D reduction of the O26 STEC strain was achieved when curd was heated at 68 °C for 2.6 to 6.3 min or at 80 °C for 2.1 to 2.3 min. Greater resistance was observed for the O157 strain at 68 °C because k(max) was 1.48 min(-1). The model estimates can support cheesemakers in defining appropriate process criteria needed to control possible STEC contamination in raw milk intended for the production of Mozzarella.

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Effect of cell immobilization on heat-induced sublethal injury of Escherichia coli, Salmonella Typhimurium and Listeria innocua

Cited by 51 publications

References 86 publications

Detection of Thermal Sublethal Injury in Escherichia coli via the Selective Medium Plating Technique: Mechanisms and Improvements

Detection of Thermal Sublethal Injury in Escherichia coli via the Selective Medium Plating Technique: Mechanisms and Improvements

Effect of cell immobilization on the growth dynamics of Salmonella Typhimurium and Escherichia coli at suboptimal temperatures

Thermal inactivation kinetics of Shiga toxin-producing Escherichia coli in buffalo Mozzarella curd

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