Modelling the growth of Listeria monocytogenes in dynamic conditions

A recurrent neural network for the prediction of Listeria monocytogenes growth under pH and a(w) variable conditions was developed. The use of this model offered the possibility to take into account the consequences of the variations of the factors on L. monocytogenes growth. The effects of solutions, such as NaCl, acetic acid and NaOH, and their interactions on the response of L. monocytogenes cells were studied. Furthermore, the results showed the capacity of the recurrent neural network to predict growths carried out in different experimental conditions without using those used for its elaboration.     

A predictive model that evaluates the effect of growth conditions on the thermal resistance of Listeria monocytogenes

A predictive model for Listeria monocytogenes was developed using cells grown in different pH and milkfat levels before subsequent thermal inactivation in identical pH and milkfat conditions. Inactivation of the cells used combinations of temperature (55, 60, 65 degrees C), pH (5.0, 6.0, 7.0), and milkfat (0%, 2.5%, 5.0%) in a complete 3 x 3 x 3 factorial design with each test done in triplicate. A modified Gompertz equation was used to model nonlinear survival curves with the following three parameter estimates: A for the shouldering region, B for the maximum death rate, and C for the tailing region. All treatment sets were analyzed together in a regression model using the modified Gompertz equation. There was good confidence in the overall model when it was used to predict values for the entire data set. The correlation of determination, R2, between the observed log surviving fraction (LSF) of cells from each of the conditions studied in the experiment, for the overall model was 0.811. For the A and B parameter estimates, temperature or milkfat alone, and the interaction of temperature and milkfat significantly (p < 0.05) affected the shouldering region and maximum death rate of a survival curve, respectively. These results were compared to a previously published predictive model, generated for cells grown under optimum conditions (pH 7.0, 0% milkfat), where pH was the only significant (p < 0.05) factor affecting the shoulder region. These results suggested that the conditions of the growth environment had an important impact on survival curve shape and the estimates of the predictive model. Specifically, there were more factor interactions involving temperature and milkfat level. These growth factors affected the shoulder region and maximum rate of death of the survival curve when cells were grown in identical medium conditions to which they were heated. Differences related to shouldering and inactivation rates for cells grown in different conditions may have important and practical importance for estimating inactivation of L. monocytogenes. This study provides some evidence on the importance of growing conditions when evaluating microbial heat resistance.     

Analysis and probabilistic simulation of Listeria monocytogenes inactivation in cooked beef during unsteady heating

This study was aimed at predicting the inactivation of Listeria monocytogenes in cooked beef during unsteady heating. A one-step approach was firstly applied to determine the thermodynamic coefficient of the beef sample. Then, inactivation kinetics was estimated by constructing the empirical heat transfer model and the log-linear dynamic inactivation model. Validations showed that the integrated model could accurately describe L monocytogenes dynamic inactivation under unsteady heating conditions. With the bootstrap and Monte Carlo approach, the stochastic inactivation of L. monocytogenes could be further simulated by considering the model uncertainty and strain variability. A higher uncertainty of the time for 4 log CFU g^-1 reduction presented when the endpoint temperature was relatively lower. The present study might provide a practical way to predict the bacterial dynamic and stochastic inactivation for further probabilistic risk assessment.     

Modelling thermal inactivation of Listeria monocytogenes in sucrose solutions of various water activities

The heat resistance of Listeria monocytogenes was determined in sucrose solutions with water activity (a(w)) ranging from 0.99 to 0.90. At all temperatures investigated shape of the survival curves depended on the a(w) of the treatment medium. The survival curves for a(w)=0.99 appeared to be linear, for a(w)=0.96 were slightly upwardly concaved and for a(w)=0.93 and 0.90 were markedly concave upward. A mathematical model based on the Weibull distribution provided a good fit for all the survival curves obtained in this investigation. The effect of the temperature and a(w) on the Weibull model parameters was also studied. The shape parameter (p) depended on the a(w) of the treatment medium but in each medium of different a(w) the temperature did not have a significant effect on this parameter. The p parameter followed a linear relationship with a(w). The scale parameter (delta) decreased with the temperature following an exponential relationship and increased by decreasing the a(w) in the range from 0.99 to 0.93. However the delta parameter of survival curves obtained at a(w)=0.90 were lower than those obtained at a(w)=0.93. A mathematical model based on the Weibull parameters was built to describe the joint effect of temperature and a(w) on thermal inactivation of L. monocytogenes. This model provides a more complete information on the influence of the a(w) on the L. monocytogenes than the data initially generated. The model developed indicated that the effect of the a(w) on the thermal resistance of L. monocytogenes varied depending upon the temperature of treatment.     

Effect of preinoculation growth media and fat levels on thermal inactivation of a serotype 4b strain of Listeria monocytogenes in frankfurter slurries

Preinoculation growth conditions and fat levels were evaluated for effects on the heat resistance of Listeria monocytogenes strain MFS 102 in formulated frankfurter slurries and on frankfurter surfaces. Comparison of linear inactivation rates (D-values) for cells heated in frankfurter slurry showed that growth conditions were significant (P<0.05) factors affecting subsequent thermal resistance. The average D(60 degrees C)-values for the five preinoculation growth media tested from most resistant to least heat resistant were: tryptic soy broth with 0.6% yeast extract (TSBYE) (2.2 min) and 8.5% fat slurry (2.2 min), followed by 23% fat slurry (1.7 min) and 11% fat slurry (1.7 min), and then TSYBE with quaternary ammonium compounds added (TSBYE+Q) (1 min). The fat level in the frankfurter heating media also had a significant (P<0.05) effect on the thermal death rate of L. monocytogenes. Cells heated in 8.5% fat slurry had a significantly higher (P<0.05) D(60 degrees C)-value (2.2 min) than those heated in 11% fat (1.0 min) and 23% fat slurry (0.9 min). Growth media (TSBYE, 8.5% fat slurry, and TSBYE+Q), and fat level (15% and 20%), however, were not significant factors (P>0.05) affecting thermal inactivation rates on frankfurter surfaces. Heat inactivation rates were consistently higher on frankfurter surfaces compared to similar treatments done in frankfurter slurry. On frankfurter surfaces, a 2.3- to 5.1-log(10) reduction was achieved after 15 min depending on frankfurter surface type. The time necessary to achieve a 3-log(10) reduction using post-processing pasteurization of frankfurters in a hot water-bath at 60 degrees C almost doubled for cells grown in TSBYE and heated in 23% fat frankfurter slurry (19.6 min) versus cells grown and heated in 8.5% fat frankfurter slurry (10.8 min).     

Influence of prior growth conditions, pressure treatment parameters, and recovery conditions on the inactivation and recovery of Listeria monocytogenes, Escherichia coli, and Salmonella Typhimurium in turkey meat

The relatively high prevalence of Listeria monocytogenes, Escherichia coli O157:H7, and Salmonella enterica serovar Typhimurium in various food products is of great concern to the food industry. The objective of this study was to determine the pressure-inactivation of the pathogens in a representative food model as affected by prior growth temperature, physiological age of the culture, pressure level and treatment temperature. The effect of post-treatment conditions (incubation temperature and gas atmosphere) on the bacterial recovery was also determined. The pathogens being studied were inoculated into sterile turkey breast meat to a final level of ca. 3 logCFU/g and then grown to two stages, the early stage (representative of exponential phase) and late stage (representative of stationary phase), at 15, 25, 35, and 40 °C. Turkey meat samples were pressure-treated at 400 and 600 MPa for 2 min at initial sample temperatures of 4, 20 and 40 °C. Following treatment, bacterial counts in the samples were determined aerobically or anaerobically at incubation temperatures of 15, 25, 35, and 40 °C. Pressure inactivation of the bacterial pathogens increased as a function of the pressure levels and treatment temperatures. Generally speaking, early stage cells were more resistant than late stage cells (P<0.05). The incubation gas atmosphere did not affect bacterial recovery. Bacteria grown at 15-35 °C underwent higher population reductions than those grown at 40 °C. With regard to recovery temperatures, low temperatures promoted greater recovery of injured early and late stage cells than higher temperatures (P<0.05). This study indicates the importance of environmental conditions to which bacteria are exposed prior to pressure treatment and recovery conditions of the bacteria after pressure treatment when considering the adequacy of pressure treatments to enhance the microbiological safety of foods.     

Influence of partial inactivation on growth of Listeria monocytogenes under sub-optimal conditions of increased NaCl concentration or increased acidity

The effect of partial inactivation with lactic acid (LA), liquid chlorine dioxide (ClO₂) and intense light pulses (ILP) on injury and post-treatment growth under increased NaCl concentration and reduced pH values of Listeria monocytogenes strains was investigated. Inactivation levels and the percentage of sub-lethal were dependent upon strain and type of inactivation technique used. Comparison of the mean time-to-detection (TTD) values under suboptimal conditions (increased NaCl concentration or reduced pH) showed that the longest TTD was at every pH observed for the cultures treated with ClO₂, followed by LA and ILP. Under increased NaCl concentration LA treated cells required the longest TTD, followed by ClO₂ and ILP, respectively. Significant difference in TTD between untreated and cultures treated with ClO₂ and LA was observed. Recovery of ILP treated cultures was not always different from untreated cultures. The extended post-treatment effect based on the growth retardation or inhibition of injured cells under sub-optimal conditions is suggested as an important tool in conditioning of microbial food safety.Industrial relevanceSmall and medium sized enterprises (SMEs) are the backbone of the European economy. They are a key source of jobs and a breeding ground for implementation of research results. They are however the most sensitive of all to changes in the production practices coming as a consequence of increased consumers' awareness regarding fresh and natural-like foods. In order to respond to the changed consumption pattern, non-heat and so-called mild technologies have emerged. This research as a part of the EU Pathogen Combat project is tailor made to answer some of the burning issues when it comes to “mild” decontamination. Among the more established technologies used here is decontamination with lactic acid, followed by chlorine dioxide. Both are now under the eye of EU policy makers who are seeking relevant facts to adjust or not to adjust EU policy regarding decontamination of foods. Latest EFSA opinions have already pushed these agents forward, but relevant scientific facts were declared missing. Moreover, intense light pulses, as non-chemical alternative to pasteurization have a considerable potential not only in food surface decontamination, but also in the decontamination of packaging materials, industrial surfaces etc. The present research brought new facts into the light that might have a credible influence on understanding pros and cons of lactic acid, chlorine dioxide and intense light pulses as decontamination agents. The post-treatment, based on sublethal injury, effect is suggested as an important extension tool in shelf life extension and safety barrier.     

Effect of sodium lactate on thermal inactivation of Listeria monocytogenes and Salmonella in ground chicken thigh and leg meat

The effect of sodium lactate on thermal inactivation D- and z-values of Listeria monocytogenes and Salmonella was determined for chicken thigh and leg meat. At 55 to 70 degrees C, the D-value of L. monocytogenes in ground chicken thigh and leg meat with the addition of 4.8% sodium lactate (4.8 g sodium lactate per 100 g of meat) was 53 to 75% higher than that in the meat without sodium lactate. No significant difference was found for the D-values of Salmonella at 55 to 70 degrees C between the meat with and that without sodium lactate (4.8%. wt/wt). The z-values of both L. monocytogenes and Salmonella were not affected by sodium lactate (4.8%). The results from this study are useful for predicting thermal process lethality of L. montocytogenes and Salmonella in formulated chicken thigh and leg meat products.     

Thermal inactivation, growth, and survival studies of Listeria monocytogenes strains belonging to three distinct genotypic lineages

Twenty-one Listeria monocytogenes strains belonging to three different genotypic lineages were evaluated for differences between lineages and between individual strains with respect to thermal inactivation, growth, and survival. Three sets of heat inactivation conditions (60 degrees C, pH 6.0, and 0.5 M lactate; 55 degrees C, pH 6.0, and 0.5 M lactate; and 50 degrees C, pH 4.0, and 0.5 M lactate) were used on strains grown in modified brain heart infusion (BHI) broth with and without glucose. Two sets of growth conditions (35 degrees C, pH 6.5, and 0.1 M lactate and 5 degrees C, pH 6.5, and 0.1 M lactate) were used with modified BHI broths to determine lag phases and exponential growth rates. Two sets of conditions (28 degrees C, pH 4.0, and 1 M lactate and 28 degrees C, pH 4.5, and 0.5 M lactate) were used with modified BHI broth to determine survival times (D-values). Thermal inactivation D-values were consistently lowest for lineage III, but differences were not significant for any set of conditions tested. Some significant differences were observed between lineages with respect to some of the growth and survival conditions tested. Extensive strain-to-strain variation was observed for all parameters tested. Average coefficients of variation for the thermal inactivation, growth, and survival studies were 0.31, 0.18, and 0.26, respectively. Strain-to-strain variations were approximately equal to the uncertainties associated with the analytical procedures. The results obtained indicate a diversity among strains encountered in food processing that must be accounted for in process calculations and risk assessments.     

接种量对单增李斯特菌生长期及生长界面的影响

为了初步了解接种量对单增李斯特菌生长状况及生长/非生长界面的影响,本实验对单增李斯特菌在0、4、10、25℃下通过培养菌液在600nm下的吸光光度值对其生长周期曲线分别进行了测定,并分析了不同接种量的单增李斯特菌菌液在25℃下的生长周期状况,探讨了纯培养条件下不同盐度和pH下,接种量对单增李斯特菌生长/非生长状况的影响。结果表明:不同的温度下,单增李斯特菌的生长周期有很大的差别;而在相同温度下,接种量对单增李斯特菌的生长周期有较大的影响,随着接种水平的降低,菌种生长所需的延滞时间越长,接种量为107CFU/mL时,其生长延滞期为0~4h,而当接种量减少为10CFU/mL时,其生长延滞期为0~16h;而对于单增李斯特菌的生长/非生长界面而言,接种量对其也有一定的影响,但其作用机制还有待进一步深入的研究。      

Effect of the substrate's microstructure on the growth of Listeria monocytogenes

The effect of the microstructure of the medium on the growth of the food-borne pathogen Listeria monocytogenes was studied. The pathogen's growth kinetics was evaluated using liquid substrates and gels formed from different concentrations of sodium alginate (3.0% w/w) and gelatin (0–30.0% w/w). These results were further verified using a model dairy product with solid concentrations varying from 10.0 to 40.0% w/w. The pathogen's growth was faster in the liquid media than in the gels regardless of the gelling agent employed. The substrate's microstructure, apart from altering the growth pattern from planktonic to colonial, resulted in microbial growth suppression; however, each system affected the microorganism's growth in a different way. The suppressing effect of the substrate's microstructure on microbial growth was also dependent on temperature, while the presence of glucose in the solid medium accelerated microbial growth, thus reducing substantially the difference in growth kinetics between the gels and the liquid media. Any increase in the hydrocolloid concentration, which was also reflected in the rheological properties of the structured samples, resulted in a reduction of growth rate and in an increase of the lag phase of the pathogen. Overall, the gelation of the medium was found to exert a stress on the microorganism since the sol–gel transition, when the pathogen was already at the exponential growth phase, resulted in an additional lag phase or a decrease in the growth rate. The relationship between maximum specific growth rate and loss tangent of the gels (tanδ = G″/G′) was explored, pointing to the possible use of a single structural parameter to describe food matrix effects on microbial growth kinetics.     

Influence of sodium pyrophosphate on thermal inactivation of Listeria monocytogenes in pork slurry and ground pork

The thermal inactivation (55–62·5°C) of Listeria monocytogenes in pork slurry and ground pork that contained 0, 0·25 or 0·5% sodium pyrophosphate (SPP) was evaluated. Surviving cells were enumerated on Modified Oxford Medium. Decimal reduction (D)-values in pork slurry control (0% SPP) were 8·15, 2·57, 0·99, and 0·18 min, at 55, 57·5, 60 and 62·5°C, respectively; D-values in ground pork ranged from 15·72 min at 55°C to 0·83 min at 62·5°C. D-values in pork slurry that contained 0·25% SPP (w/v) were 4·75, 1·72, and 0·4 min, at 55, 57·5, and 60°C respectively; the values in ground pork ranged from 16·97 at 55°C to 0·80 min at 62·5°C. At 62·5°C,L. monocytogenes in slurry that contained SPP were killed too rapidly to allow determination of the D-value. Addition of 0·5% SPP further decreased (P<0·05) the heat resistance of L. monocytogenes in pork slurry but not in ground pork. The z-values in slurry ranged from 4·63 to 5·47°C whereas higher z-values (5·25 to 5·77°C) were obtained in ground pork. Degradation of SPP to orthophosphates in ground pork was two or three times greater than in pork slurry. Possible reasons for failure of SPP to reduce the thermal resistance of L. monocytogenes in ground pork are discussed.     

Formation of biofilms by Listeria monocytogenes under various growth conditions

Eight strains of Listeria monocytogenes (7644, 19112, 15313, Scott A, LCDC, 10403S, SLCC, and 1370) produce biofilms when grown on polyvinyl chloride microtiter well plates. The growth medium (tryptic soy broth [TSB] or modified Welshimer's broth [MWB] at 32 degrees C) influenced the amount of biofilm formed; maximum biofilms were formed in MWB by six strains and in TSB by the remaining two strains. This result suggests that the growth medium is critical in development of L. monocytogenes biofilm. This organism also produced biofilms on stainless steel chips. Biofilm formation on these chips was observed following growth in TSB at 4, 20, and 37 degrees C. After 20 h of incubation at 20 or 37 degrees C, the cell density was approximately 10(6) CFU per chip, and after 4 days incubation at 4 degrees C, the cell density was 10(5) CFU per chip. L. monocytogenes strain Scott A biofilm formation on stainless steel chips was visualized using scanning electron microscopy, which revealed dense aggregates of cells held together by meshlike webbing.     

Effect of the inoculum size on Listeria monocytogenes growth in structured media

Obtaining quantitative data concerning the relative impact of various factors that may influence bacterial growth is of great importance for microbial risk assessment and predictive microbiology. The objective of this work was to investigate the effect of the initial Listeria monocytogenes density on all the growth parameters of this pathogen (lag phase duration, growth rate and maximum population density attained) on a sterile solid model system mimicking smoked fishery products, and in real cold-smoked salmon, a product likely to be contaminated with L. monocytogenes. Growth of the pathogen was monitored using a sensitive enumeration method, recently developed, based on membrane filtration followed by the transfer of the filter on a selective media [Gnanou Besse, N., Audinet, N., Beaufort, A., Colin, P., Cornu, M. and Lombard, B., 2004. A contribution to the improvement of Listeria monocytogenes enumeration in smoked salmon. International Journal of Food Microbiology, 91, 119-127.]. Depending on the experimental conditions, we found a significant effect of the inoculum size, both on lag phase duration, and on the maximal population attained. Moreover, the effect of the inoculum size on the growth of L. monocytogenes was dependent on a complex set of interactions. Factors which have appeared to impact on this effect include the cells physiological state, the background microflora, the texture of the media and the packaging system. It is important to understand how these interactions affect the growth of Listeria in order to predict and control its development in food.     

Effect of relative inoculum concentration on Listeria monocytogenes growth in co-culture

Growth suppression of multi-species bacterial populations in batch cultures by a single 'dominant' strain has been referred to in the literature as the 'Jameson Effect'. The effect is often attributed to production of specific inhibitors of growth by one species against another. To explore its basis, we hypothesised that the Jameson Effect is often a non-specific interaction and that growth inhibition of species in co-culture can be controlled by manipulation of inoculum concentration and growth rate so as to enable a selected species to achieve stationary phase first. The hypothesis was assessed by co-culturing pairs of bacterial species under conditions selected to ensure that both strains grew at a similar rate and manipulating the initial concentration of each species. Specifically, the effect of inoculum concentration on the growth kinetics of Listeria monocytogenes when co-cultured in complex laboratory media with Escherichia coli, Pseudomonas fluorescens or a commercial strain of the lactic acid bacterium, Lactobacillus plantarum, was studied. Starting numbers of the second strain were either higher than ( approximately 10(6) cfu mL(-1)), equal to ( approximately 10(4) cfu mL(-1)) or lower than ( approximately 10(3) cfu mL(-1)) L. monocytogenes. In most trials, the initial inoculum concentration governed which species became dominant and suppressed the growth of the other strain. L. monocytogenes was suppressed by all other strains when its inoculum level was lower. Conversely, when L. monocytogenes was initially present at higher concentration than either P. fluorescens or L. plantarum, their growth was suppressed. E. coli, however, was not suppressed by L. monocytogenes even when the E. coli density was initially lower. While simple competition for nutrients could explain most of the observations, in some co-culture experiments pH reduction also seemed to play a role in inhibition of growth of some species. In other cases, available growth substrates were apparently not utilised by both co-cultured species, and the Jameson Effect did not occur. Thus, while it appears that under many conditions the Jameson Effect may be largely due to non-specific inhibition, more complex interactions between co-cultured strains involving species-specific pH limits for growth and differential utilisation of growth substrates may also occur and confound the simple Jameson Effect.     

Effect of combining nisin and/or lysozyme with in-package pasteurization on thermal inactivation of Listeria monocytogenes in ready-to-eat turkey bologna

Achieving a targeted lethality with minimum exposure to heat and preservation of product quality during pasteurization is a challenge. The objective of this study was to evaluate the effect of nisin and/or lysozyme in combination with in-package pasteurization of a ready-to-eat low-fat turkey bologna on the inactivation of Listeria monocytogenes. Sterile bologna samples were initially treated with solutions of nisin (2 mg/ml = 5,000 AU/ml = 31.25 AU/cm2), lysozyme (10 mg/ml = 80 AU/ml = 0.5 AU/cm2), and a mixture of nisin and lysozyme (2 mg/ml nisin + 10 mg/ml lysozyme = 31.75 AU/cm2). Bologna surfaces were uniformly inoculated with a Listeria suspension resulting in a population of approximately 0.5 log CFU/cm2. Samples were vacuum packaged and subjected to heat treatment (60, 62.5, or 65 degrees C). Two nonlinear models (Weibull and log logistic) were used to analyze the data. From the model parameters, the time needed to achieve a 4-log reduction was calculated. The nisin-lysozyme combination and nisin treatments were effective in reducing the time required for 4-log reductions at 62.5 and 65 degrees C but not at 60 degrees C. At 62.5 degrees C, nisin-lysozyme-treated samples required 23% less time than did the control sample to achieve a 4-log reduction and 31% less time at 65 degrees C. Lysozyme alone did not enhance antilisterial activity with heat. Results from this study can be useful to the industry for developing an efficient intervention strategy against contamination of ready-to-eat meat products by L. monocytogenes.     

产抗菌素乳酸菌的组合应用对牛肉中李斯特菌污染的抑制作用研究

研究了弯曲乳酸杆菌和乳酸片球菌对低温冷藏牛肉中李斯特菌的混合协同抑制作用。李斯特菌、弯曲乳酸杆菌(产细菌素sakacinP)和乳酸片球菌(产生片球菌素AcH),单独或混合接种于冷鲜牛肉中,4℃下储藏6周。单一接种弯曲乳酸杆菌或乳酸片球菌均能对李斯特菌起到抑制作用,但一周后均出现李斯特菌再次污染现象;然而混合接种弯曲乳酸杆菌和乳酸片球菌能将对李斯特菌的抑制期延长至第六周,之后才出现反弹现象,且李斯特菌数低于10cfu·g-1。因此,应用组合产细菌素菌株能有效延长对李斯特菌的抑制作用。     

Temperature-assisted pressure inactivation of Listeria monocytogenes in turkey breast meat

Ready-to-eat turkey breast meat samples were surface-inoculated with a five-strain cocktail of Listeria monocytogenes cultures to a final concentration of approximately 10(7) CFU/g. The inoculated meat samples were vacuum-packaged and pressure treated at 300 MPa for 2 min, 400 MPa for 1 min, and 500 MPa for 1 min at initial sample temperatures of 1, 10, 20, 30, 40, 50, and 55 degrees C. L. monocytogenes was most resistant to pressure at temperatures between 10 and 30 degrees C. As temperature decreased below 10 degrees C or increased over 30 degrees C, its pressure sensitivity increased. This enhanced inactivation effect was more pronounced when meat samples were treated at higher temperature than at lower temperature. For example, a 1-min treatment of 500 MPa at 40 degrees C reduced the counts by 3.8 log(10), while at 1 and 20 degrees C the same treatment reduced counts by 1.4 and 0.9 log(10), respectively (P<0.05). The survival curves of L. monocytogenes were obtained at 300 MPa and 55 degrees C, 400 MPa and 50 degrees C, and 500 MPa and 40 degrees C. With increasing treatment time, the three survival curves showed a rapid initial drop in bacteria counts with a diminishing inactivation rate or tailing effect. The survival data were fitted with a linear and a nonlinear, Weibull, models. The Weibull model consistently produced better fit to the survival data than the linear model.     

On the different growth conditions affecting silver antimicrobial efficacy on Listeria monocytogenes and Salmonella enterica

Silver is known to inhibit microorganisms and therefore it is an ideal candidate for its incorporation in a wide variety of materials for food applications. However, there is still a need for understanding how silver prolonged exposure to bacterial contamination affects the bioavailability of the active silver species. In the present study, growth curves of Listeria monocytogenes and Salmonella enterica were performed for 3-5days in Tryptic Soy Broth (TSB) and M9 minimal medium (M9) in the presence of silver ions and silver solutions previously in contact with the growth media. The cultivability of the bacteria under these conditions was correlated with the viability of the bacterial populations as measured by flow cytometry analysis (FC) using a LIVE/DEAD BacLight kit. It was found that, after a period where viable counts were not detected, bacterial populations recovered and were able to proliferate in most cases. The resuscitation of the cultures was explained by both the existence of a resilient fraction of bacteria in a compromised state and the parallel inactivation of the silver species. This inactivation was found to be highly influenced by time dependant chemical reactions taking place in the environment of exposure, producing differences of at least 3 fold between results for nutrient rich environments and results for limiting environments. This study points out the need for understanding these chemical interactions and bacterial mechanisms of adaptation and may have relevance in the design of silver-based antimicrobial systems for food-related applications.