Growth Kinetics Of Listeria Monocytogenes Research Articles

Prior freezing impact on the growth kinetics of Listeria monocytogenes in hot dog sausages

Listeria monocytogenes adapts to low-temperature environments and grows rapidly at room temperature. This bacterium is associated with several foodborne outbreaks due to cold chain breaks, particularly ready-to-eat foods such as sausages. The present study evaluated how frozen storage (-10 °C) for 30 and 90 days of hot dog sausages influences the bacterial growth kinetics between 7 and 30 °C under isothermal conditions. L. monocytogenes growth measurements were based on the ISO 11290-2 standard, and the mathematical model of Baranyi and Roberts was used to describe the bacterial growth. The sausages were incubated with around 2 log CFU/cm2, remaining constant for up to 90 days. However, prior freezing periods influenced bacterial growth behavior, mainly at chilled conditions (7 and 10 °C), increasing the maximum specific growth rate by 60%, lag phase time by 72%, and physiological state of the cells by 166%. The maximum population was not influenced by prior freezing. The proposed model fits the isothermal conditions studied. L. monocytogenes, after food thawing, grows at the same or higher rate than before freezing, which could represent a risk if the manufacturer's recommendations are not followed.

Growth Kinetics of Listeria monocytogenes and Salmonella enterica on Dehydrated Vegetables during Rehydration and Subsequent Storage.

Dehydrated vegetables have low water activities and do not support the proliferation of pathogenic bacteria. Once rehydrated, vegetables can be incorporated into other foods or held for later use. The aim of this study was to examine the survival and proliferation of Listeria monocytogenes and Salmonella enterica on dehydrated vegetables during rehydration and subsequent storage. Carrots, corn, onion, bell peppers, and potatoes were heat dehydrated, inoculated at 4 log CFU/g, and rehydrated at either 5 or 25 °C for 24 h. Following rehydration, vegetables were stored at 5, 10, or 25 °C for 7 d. Both L. monocytogenes and S. enterica survived on all vegetables under all conditions examined. After 24 h of rehydration at 5 °C, pathogen populations on the vegetables were generally <1.70 log CFU/g, whereas rehydration at 25 °C resulted in populations of 2.28 to 6.25 log CFU/g. The highest growth rates during storage were observed by L. monocytogenes on potatoes and S. enterica on carrots (2.37 ± 0.61 and 1.63 ± 0.18 log CFU/g/d, respectively) at 25 °C when rehydration occurred at 5 °C. Results indicate that pathogen proliferation on the vegetables is both rehydration temperature and matrix dependent and highlight the importance of holding rehydrated vegetables at refrigeration temperatures to hinder pathogen proliferation. Results from this study inform time and temperature controls for the safety of these food products.

Effects of temperature abuse on the growth and survival of Listeria monocytogenes on a wide variety of whole and fresh-cut fruits and vegetables during storage

Twenty types of fruits and vegetables representing a broad range of fresh produce categories were assessed for the growth potential and growth kinetics of Listeria monocytogenes under conditions reflecting commercial practices for storage and distribution and conditions reflecting sustained temperature abuse. Whole and fresh-cut produce was obtained from various commercial sources and inoculated with L. monocytogenes strains to evaluate the survival and growth for up to 25 days, depending on the projected commercial storage or retail shelf life for each commodity. The L.monocytogenes populations showed a sustained decline on all tested whole fruits, including avocado, blueberry, grape, mango, peach, green pepper, and tomato. Under “normal” storage conditions (defined as those reflective of common commercial practices), significant L. monocytogenes growth was only observed on fresh-cut cantaloupe (∼0.8 log) and fresh-cut mango (∼0.6 log). Exposure to temperature abuse conditions did not change the overall trends of L. monocytogenes survival on the whole fruits but did result in significant growth on several fresh-cut products, including celery, cauliflower, mango, onion, romaine lettuce, and cantaloupe. After inoculation on certain products (e.g., fresh-cut carrot and whole peach), L. monocytogenes seemed to lose cultivability rapidly but did retain viability as determined by the maintenance of cell membrane integrity.

Inactivation and Subsequent Growth Kinetics of Listeria monocytogenes After Various Mild Bactericidal Treatments.

This study was carried out to investigate the effects of mild heat, lactic acid, benzalkonium chloride and nisin treatments on the inactivation, sublethal injury, and subsequent growth of Listeria monocytogenes. Results showed that the Bigelow model successfully described the thermal inactivation kinetics, while the Log-linear model with tail consistently offered the most accurate fit to LA, BC, and nisin inactivation curves of cells. Differential plating indicated that percentage of sublethal injury for nisin treated cells was significantly higher than that for the other three treatments. Compared to non-treated cells, significant extension of lag time was observed for all treated cells. The longer exposures to heat treatment contributed to the extended lag time of the survivors. While for LA, BC and nisin treated cells, the longest lag time was not observed at the most severe treatment conditions. The correlation analysis of sublethal injury percentage on the duration of lag time revealed that only heat treatment showed the significant correlation. Overall, the lag time analysis could evaluate a wide range of bacterial injury. Lag time of treated cells was significantly influenced by stress treatments and temperatures of recovery, however, there were not any significant changes in the maximum specific growth rate between treated and non-treated cells under isothermal recovery conditions. The information generated from this study is valuable for utilizing intervention strategies in the elimination or growth inhibition of L. monocytogenes.

Modelling the growth kinetics of Listeria monocytogenes in pasta salads at different storage temperatures and packaging conditions

The aim of this study was to model Listeria monocytogenes growth kinetics in ready to eat full meal pasta salads, containing fresh and cooked ingredients. With this aim, laboratory prepared salads, representing two formulations of commercial pasta salads, were spiked with L. monocytogenes and tested under categorised packaging and storage temperature conditions. L. monocytogenes enumeration results collected in 15 different laboratory prepared salad datasets were analysed with primary and secondary models. The models showing the best fit to describe L. monocytogenes growth kinetics in the laboratory prepared salads were then validated within commercial pasta salads. Baranyi no-lag was the best primary model fitting datasets collected at 12 °C, whereas the exponential model gave the best results for datasets collected at 4 °C. The maximum microbial specific growth rate (μmax) mean values obtained at 4 and 12 °C for salads packaged under air packaging conditions were 0.008 ± 0.003 and 0.036 ± 0.006 log10 (cfu/g) h−1, respectively. At the same temperatures, the μmax mean values obtained under modified atmosphere were 0.005 ± 0.005 and 0.026 ± 0.005 log10 (cfu/g) h−1, respectively. The Gamma secondary model predicted the growth kinetics of L. monocytogenes at both temperatures and packaging conditions and the μmax at the optimum temperature and the optimum pH for Listeria growth (μopt) estimated by the model corresponded to 0.247 ± 0.009 log10 (cfu/g) h−1. Baranyi model without lag phase was used to generate growth kinetics under different scenarios. In the comparison of the predicted log10 concentrations respect to the observed ones the residues rarely exceeded 1 Log10 cfu/g. The selected models can be applied to describe the growth kinetics of L. monocytogenes in similar types of pasta salads with comparable pH, shelf life and storage conditions.

Closing gaps for performing a risk assessment on Listeria monocytogenes in ready‐to‐eat (RTE) foods: activity 2, a quantitative risk characterization on L. monocytogenes in RTE foods; starting from the retail stage

Closing gaps for performing a risk assessment on Listeria monocytogenes in ready‐to‐eat (RTE) foods: activity 2, a quantitative risk characterization on L. monocytogenes in RTE foods; starting from the retail stage

Modeling the Effect of Storage Temperatures on the Growth of Listeria monocytogenes on Ready-to-Eat Ham and Sausage

The aim of this study was to model the growth kinetics of Listeria monocytogenes on ready-to-eat ham and sausage at different temperatures (4 to 35°C). The observed data fitted well with four primary models (Baranyi, modified Gompertz, logistic, and Huang) with high coefficients of determination (R2 > 0.98) at all measured temperatures. After the mean square error (0.009 to 0.051), bias factors (0.99 to 1.06), and accuracy factors (1.01 to 1.09) were obtained in all models, the square root and the natural logarithm model were employed to describe the relation between temperature and specific growth rate (SGR) and lag time (LT) derived from the primary models. These models were validated against the independent data observed from additional experiments using the acceptable prediction zone method and the proportion of the standard error of prediction. All secondary models based on each of the four primary models were acceptable to describe the growth of the pathogen in the two samples. The validation results indicate that the optimal primary model for estimating the SGR was the Baranyi model, and the optimal primary model for estimating LT was the logistic model in ready-to-eat (RTE) ham. The Baranyi model was also the optimal model to estimate the SGR and LT in RTE sausage. These results could be used to standardize predictive models, which are commonly used to identify critical control points in hazard analysis and critical control point systems or for the quantitative microbial risk assessment to improve the food safety of RTE meat products.

Growth of Listeria monocytogenes in salmon roe – A kinetic analysis

The objective of this study was to investigate the growth kinetics of Listeria monocytogenes in unsalted and salted (3%) salmon roe. Growth curves, developed using inoculated samples incubated at constant temperatures between 5 and 30 °C, were analyzed by curve-fitting to the Huang and Baranyi models using the USDA IPMP 2013. The experimental results showed that L. monocytogenes in salted samples exhibited approximately 40% longer lag times than the cells in unsalted samples under the same temperature condition, while the rates of bacterial growth were not affected by the addition of salt. The Ratkowsky square-root (RSR) model, Huang square-root (HSR) model, and an Arrhenius-type model were all shown suitable for evaluating the effect of temperature on specific growth rates. The estimated nominal minimum growth temperature in the RSR model was −0.5 °C, whereas the minimum growth temperature in HSR model was 2.57 °C. The HSR models may be more suitable for describing the temperature effect in salted salmon roe. The lag times of L. monocytogenes were found to change log-linearly with the specific growth rates. The mean h0 in the Baranyi model was 0.742 in unsalted samples and 1.193 in salted samples, and did not appear to change with temperature in a systematic manner. In summary, kinetic models were developed for examining the effect of temperature on growth of L. monocytogenes in unsalted and salted salmon roe samples. The results may be used by the food industry and regulatory agencies to estimate the growth of L. monocytogenes in salmon roe, and to conduct risk assessments of this microorganism.

Development of Predictive Models for the Growth Kinetics of Listeria monocytogenes on Fresh Pork under Different Storage Temperatures

This study was conducted to develop a predictive model to estimate the growth of Listeria monocytogenes on fresh pork during storage at constant temperatures (5, 10, 15, 20, 25, 30, and 35°C). The Baranyi model was fitted to growth data (log CFU per gram) to calculate the specific growth rate (SGR) and lag time (LT) with a high coefficient of determination (R(2) > 0.98). As expected, SGR increased with a decline in LT with rising temperatures in all samples. Secondary models were then developed to describe the variation of SGR and LT as a function of temperature. Subsequently, the developed models were validated with additional independent growth data collected at 7, 17, 27, and 37°C and from published reports using proportion of relative errors and proportion of standard error of prediction. The proportion of relative errors of the SGR and LT models developed herein were 0.79 and 0.18, respectively. In addition, the standard error of prediction values of the SGR and LT of L. monocytogenes ranged from 25.7 to 33.1% and from 44.92 to 58.44%, respectively. These results suggest that the model developed in this study was capable of predicting the growth of L. monocytogenes under various isothermal conditions.

“Predictive model for the growth kinetics of Listeria monocytogenes in raw pork meat as a function of temperature” [Food Control 44 (2014) 16–21

“Predictive model for the growth kinetics of Listeria monocytogenes in raw pork meat as a function of temperature” [Food Control 44 (2014) 16–21

Predictive modeling for growth of non- and cold-adapted Listeria monocytogenes on fresh-cut cantaloupe at different storage temperatures.

The aim of this study was to determine the growth kinetics of Listeria monocytogenes, with and without cold-adaption, on fresh-cut cantaloupe under different storage temperatures. Fresh-cut samples, spot inoculated with a 4-strain cocktail of L. monocytogenes (∼3.2 log CFU/g), were exposed to constant storage temperatures held at 10, 15, 20, 25, or 30 °C. All growth curves of L. monocytogenes were fitted to the Baranyi, modified Gompertz, and Huang models. Regardless of conditions under which cells grew, the time needed to reach 5 log CFU/g decreased with the elevated storage temperature. Experimental results showed that there were no significant differences (P > 0.05) in the maximum growth rate k (log CFU/g h(-1) ) and lag phase duration λ (h) between the cultures of L. monocytogenes with or without previous cold-adaption treatments. No distinct difference was observed in the growth pattern among 3 primary models at various storage temperatures. The growth curves of secondary modeling were fitted on an Arrhenius-type model for describing the relationship between k and temperature of the L. monocytogenes on fresh-cut cantaloupe from 10 to 30 °C. The root mean square error values of secondary models for non- and cold-adapted cells were 0.018, 0.021, and 0.024, and 0.039, 0.026, and 0.017 at the modified Gompertz, Baranyi, and Huang model, respectively, indicating that these 3 models presented the good statistical fit. This study may provide valuable information to predict the growth of L. monocytogenes on fresh-cut cantaloupes at different storage conditions. Listeriosis has occurred and increased along with the increased demand of fresh and fresh-cut fruits and vegetables. This study was conducted to predict the growth of non- and cold-adapted L. monocytogenes on fresh-cut cantaloupe at different temperature using mathematical model. These results can be helpful for risk assessments of L. monocytogenes in fresh-cut cantaloupe. This study provides valuable information to food handlers to choose proper storage temperatures for extending the shelf-life of fresh-cut cantaloupe.

Predictive model for the growth kinetics of Listeria monocytogenes in raw pork meat as a function of temperature

This study was performed to develop a predictive growth model of Listeria monocytogenes to ensure the safety of raw pork. The pork samples were inoculated with a cocktail of two L. monocytogenes strains ATCC 15313 and L13-2 isolated from pork and were stored at 5, 15, and 25 °C. Results were evaluated using the MicroFit program. To develop primary models, the Baranyi, modified Gompertz, and Logistic model equations were applied to the observed data. The mathematically predicted growth rate parameters were evaluated using the coefficient of determination ( R 2 ), bias factor ( B f ), accuracy factor ( A f ), and mean square error (MSE). The Baranyi model, which showed an R 2 of 0.998 and MSE of 0.006, was more suitable than the modified Gompertz and Logistic models. In validation study of secondary model, it appeared that MSE's of specific growth rate (SGR) and lag time (LT) were relatively accurate and suitable for modeling the growth of L. monocytogenes . These values indicated that the developed models were acceptable for expressing the growth of microorganisms on raw pork, which can be applied to ensure the safety of meats and to establish standards for avoiding microbial contamination. • Baranyi model is proper than others for predicting a growth of Listeria strain . • Values of μ max were inversely proportional to LT in secondary modeling. • This predictive model can be applied for food safety in meat industry.

Growth Modeling of Listeria monocytogenesin Pasteurized Liquid Egg

The growth kinetics of Listeria monocytogenes and natural flora in commercially produced pasteurized liquid egg was examined at 4.1 to 19.4°C, and a growth simulation model that can estimate the range of the number of L. monocytogenes bacteria was developed. The experimental kinetic data were fitted to the Baranyi model, and growth parameters, such as maximum specific growth rate (μ(max)), maximum population density (N(max)), and lag time (λ), were estimated. As a result of estimating these parameters, we found that L. monocytogenes can grow without spoilage below 12.2°C, and we then focused on storage temperatures below 12.2°C in developing our secondary models. The temperature dependency of the μ(max) was described by Ratkowsky's square root model. The N(max) of L. monocytogenes was modeled as a function of temperature, because the N(max) of L. monocytogenes decreased as storage temperature increased. A tertiary model of L. monocytogenes was developed using the Baranyi model and μ(max) and N(max) secondary models. The ranges of the numbers of L. monocytogenes bacteria were simulated using Monte Carlo simulations with an assumption that these parameters have variations that follow a normal distribution. Predictive simulations under both constant and fluctuating temperature conditions demonstrated a high accuracy, represented by root mean square errors of 0.44 and 0.34, respectively. The predicted ranges also seemed to show a reasonably good estimation, with 55.8 and 51.5% of observed values falling into the prediction range of the 25th to 75th percentile, respectively. These results suggest that the model developed here can be used to estimate the kinetics and range of L. monocytogenes growth in pasteurized liquid egg under refrigerated temperature.

Modeling the growth of Listeria monocytogenes on cut cantaloupe, honeydew and watermelon

A recent outbreak linked to whole cantaloupes underscores the importance of understanding growth kinetics of Listeria monocytogenes in cut melons at different temperatures. Whole cantaloupe, watermelon, and honeydew purchased from a local supermarket were cut into 10 ± 1 g cubes. A four-strain cocktail of L. monocytogenes from food related outbreaks was used to inoculate fruit, resulting in ∼103 CFU/10 g. Samples were stored at 4, 10, 15, 20, or 25 °C and L. monocytogenes were enumerated at appropriate time intervals. The square root model was used to describe L. monocytogenes growth rate as a function of temperature. The model was compared to prior models for Salmonella and Escherichia coli O157:H7 growth on cut melon, as well as models for L. monocytogenes on cantaloupe and L. monocytogenes ComBase models. The current model predicts faster growth of L. monocytogenes vs. Salmonella and E. coli O157:H7 at temperatures below 20 °C, and agrees with estimates from ComBase Predictor, and a corrected published model for L. monocytogenes on cut cantaloupe. The model predicts ∼4 log CFU increase following 15 days at 5 °C, and ∼1 log CFU increase following 6 days at 4 °C. The model can also be used in subsequent quantitative microbial risk assessments.

Modeling growth kinetics of Listeria monocytogenes in pork cuts from packaging to fork under different storage practices

The fate of Listeria monocytogenes in fresh meat products during transport and storage at retail and then at the consumer's house is poorly understood. In this study microbial behavior and concentration of L. monocytogenes in ten lots of naturally contaminated loin chops have been evaluated under four different storage scenarios throughout the product shelf life. Between-and within-lot variability on loin chops, as well as impact of environmental temperatures on pathogen growth were investigated. Secondly, distributions of the microbial concentration in the naturally contaminated lots were fitted using the maximum likelihood estimation (MLE) and variability in growth potential at dynamic storage was assessed by applying a validated predictive model from the literature, together with MonteCarlo simulation techniques. The results show that model estimations are consistent to the observed data even though variability in the growth kinetic parameters impacts the growth of L. monocytogenes in loin chops throughout the product shelf life. Overall, storage at mean refrigerator temperatures did not increase the populations of L. monocytogenes over 2 log colony forming unit per gr (cfu/g). In contrast, final storage at abuse temperatures produced microbial counts greater than 3 log cfu/g for some lots, which would require a more severe heat inactivation treatment before consumption. The results of this study should be used by risk managers to predict the effect of cooking in pathogen inactivation in loin chops, as well as the risk of cross contaminations.

Growth kinetics of Listeria monocytogenes and spoilage microorganisms in fresh-cut cantaloupe

The main objective of this study was to investigate the growth kinetics of Listeria monocytogenes and background microorganisms in fresh-cut cantaloupe. Fresh-cut cantaloupe samples, inoculated with three main serotypes (1/2a, 1/2b, and 4b) of L. monocytogenes, were incubated at different temperatures, ranging from 4 to 43 °C, to develop kinetic growth models. During storage studies, the population of both background microorganisms and L. monocytogenes began to increase almost immediately, with little or no lag phase for most growth curves. All growth curves, except for two growth curves of L. monocytogenes 1/2a at 4 °C, developed to full curves (containing exponential and stationary phases), and can be described by a 3-parameter logistic model. There was no significant difference (P = 0.28) in the growth behaviors and the specific growth rates of three different serotypes of L. monocytogenes inoculated to fresh-cut cantaloupe. The effect of temperature on the growth of L. monocytogenes and spoilage microorganisms was evaluated using three secondary models. For L. monocytogenes, the minimum and maximum growth temperatures were estimated by both the Ratkowsky square-root and Cardinal parameter models, and the optimum temperature and the optimum specific growth rate by the Cardinal parameter model. An Arrhenius-type model provided more accurate estimation of the specific growth rate of L. monocytogenes at temperatures <4 °C. The kinetic models developed in this study can be used by regulatory agencies and food processors for conducting risk assessment of L. monocytogenes in fresh-cut cantaloupe, and for estimating the shelf-life of fresh-cut products.

Modeling and predicting the simultaneous growth of Listeria monocytogenes and natural flora in minced tuna.

The growth kinetics of Listeria monocytogenes and natural flora (NF) in minced tuna from 2 to 30 °C were examined, and a simultaneous growth model was developed. The inhibiting effect of the NF on the growth of L. monocytogenes was examined by inoculating different levels of NF isolated from the minced tuna. The kinetic data were fitted to the Baranyi model and estimated the growth parameters such as specific growth rate (μ(max)), maximum population density (N(max)), and lag time. The temperature and inoculated NF dependency on the μ(max) of L. monocytogenes and NF were described by modified Ratkowsky's square-root model. As the initial NF level increased, the slopes of the square-root models were decreased for both L. monocytogenes and NF. The N(max) of L. monocytogenes was described as a function of temperature and inoculated NF level. Simultaneous growth prediction of L. monocytogenes and NF under constant temperature conditions was examined by using the differential equations based on the Baranyi model with the effect of interspecies competition substituted into the developed μ(max) and N(max) models. The root mean square errors between the model prediction and the observation for L. monocytogenes and NF were 0.42 and 0.34, respectively. Predictive simulation under fluctuating temperature conditions also demonstrated a high accuracy of simultaneous prediction for both L. monocytogenes and NF, representing the root mean square errors of 0.19 and 0.34, respectively. These results illustrate that the developed model permits accurate estimation of the behavior of L. monocytogenes in minced tuna under real temperature history until consumption.

Predictive model for growth of Listeria monocytogenes in untreated and treated lettuce with alkaline electrolyzed water

This study was performed to develop predictive models for the growth kinetics of Listeria monocytogenes in Ready-to-Eat (RTE) lettuce treated with or without alkaline electrolyzed water. Firstly, growth curves of L. monocytogenes in treated and untreated RTE lettuce were obtained at several isothermal conditions (4, 10, 15, 20, 25, 30, and 35°C) and were then fitted into Gompertz model with a high correlation coefficient (R2 > 0.99). Growth parameters such as growth rate (GR) and lag time (LT) estimated by Gompertz model were found mostly have significant difference (P 0.95), and MSE calculated from models of untreated and treated lettuce were 0.0011 and 0.0008, respectively. Also, Bf values of 0.980 and 1.034 and Af values of 1.107 and 1.118 were all in the acceptable range. This demonstrated that overall predictions showed good agreement with the experimental values, indicating success at providing reliable predictions of L. monocytogenes growth in RTE lettuce.

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 (∼ 10 6 cfu mL − 1 ), equal to (∼ 10 4 cfu mL − 1 ) or lower than (∼ 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.

Updated Models for the Effects of Temperature, Initial pH, NaCl, and NaNO2 on the Aerobic and Anaerobic Growth of Listeria monocytogenes

Data from several studies were appended to aerobic and anaerobic data sets that had been previously used to develop response surface models describing the growth kinetics of Listeria monocytogenes (Buchanan and Phillips, 1990). The expanded data sets included 709 aerobic and 358 anaerobic growth curves fitted with the Gompertz equation, and representing 189 and 150 unique combinations of four variables (temperature, pH, NaCl, NaNO2), respectively. Response surface models were developed for (1) the Gompertz B and M terms and (2) lag phase durations (LPD) and generation times (GT). In addition to modeling NaCl as a variable, a second set of response surface models was developed by substituting calculated water activity as a variable. A number of data transformations were evaluated in an attempt to better utilize no-growth data. Full quadratic models of the natural logarithm transformation of the data (no-growth data excluded) predicted values that fit the observed data well. The assignment of GT=50[emsp4 ]h and LPD=600[emsp4 ]h (the approximate maximum duration of experiments) for the variable combinations that did not support growth proved to be the most effective means of making use of the no-growth data. However, this approach did not offer any clear advantage over quadratic models where the no-growth data were excluded. Error matrices were developed for the LPD and GT models to provide 95 % confidence intervals. The agreement between observed and predicted growth kinetics was excellent considering the number and ranges of the variables encompassed in the models. The models provide reasonable predictions of the growth of L. monocytogenes in foods. The full quadratic models of LPD and GT without inclusion of the no-growth data were selected for inclusion in the USDA Pathogen Modeling Program, release 5.1.