Growth Potential Of Listeria Monocytogenes Research Articles

Microbiological and physicochemical profile of Italian steak tartare and predicting growth potential of Listeria monocytogenes

In the present study, growth potential of Listeria monocytogenes in steak tartare samples taken at retail and belonging to 13 brands marketed in Northern Italy was investigated. The samples were submitted to microbiological and chemical-physical characterization. The data obtained were used as inputs for the application of the predictive microbiology software FSSP that allows the estimation of the growth of L. monocytogenes during the shelf-life. Lactic acid bacteria, the main component of the microflora, gave variable counts among the brands (from 3.38 to 6.24 log CFU/g). pH and aw values were always higher than 5.3 and 0.96, respectively, thus they could not be considered as single efficient hurdles to prevent the growth of L. monocytogenes according to the EC Reg. 2073/2005; the same was observed for salt content (constantly <2 %) and nitrites (not quantifiable in all the samples, even if declared in some labels). Nevertheless, the combination of all the hurdles, evaluated by predictive microbiology using critical development factors, resulted in an estimated growth <0.5 log CFU/g throughout the shelf life; this output allowed us to consider all the steak tartare analysed as unfavourable substrate for L. monocytogenes growth. The information obtained could be useful for tartare producers as well as for competent authority to evaluate the effective risk concerning these typology of products.

The Effect of Fruit and Berry Pomaces on the Growth Dynamics of Microorganisms and Sensory Properties of Marinated Rainbow Trout.

Plant pomaces in suitable forms (powders, extracts) can be used in foods of animal origin to increase the nutritional value and safety of these foods. In the present study, water extracts of apple, black currant, rhubarb and tomato pomaces were used in fish marinade solutions to evaluate their effect on the growth dynamics of microorganisms and the growth potential of Listeria monocytogenes by challenge testing. The results showed that mesophilic aerobic microorganisms, Pseudomonas spp., yeasts and moulds remained at acceptable levels throughout the predetermined storage period. The challenge test results showed that the overall growth potential of L. monocytogenes in all marinated rainbow trout samples remained at ≤0.5 log10 cfu/g during the study period, and none of the marinated fish samples supported the growth of L. monocytogenes. In addition, the effect of fruit and berry pomaces on the sensory properties of marinated rainbow trout samples was evaluated. The results revealed that it is possible to effectively use fruit and berry pomaces in marinated fish products, ensuring food safety, high microbiological quality, acceptable sensory characteristics and a sufficiently long shelf life of the products.

Assessment of the Spoilage Microbiota and the Growth Potential of Listeria monocytogenes in Minced Free-Range Chicken Meat Stored at 4 °C in Vacuum: Comparison with the Spoilage Community of Resultant Retail Modified Atmosphere Packaged Products

Although current diet and nutrition trends in developed countries led the poultry industry to shift to alternative breeding/production methods, such as organic and free-range, limited data on the microbiology of alternative compared to conventional poultry meat products exist. Therefore, this study assessed the evolution and composition of the spoilage microbiota and the growth potential of inoculated (3 log cfu/g) Listeria monocytogenes in freshly minced free-range chicken meat stored at 4 °C in vacuum packages (VP; four batches) for 0, 3, 5, 7, and 10 days. Additionally, two VP batches were compared with their resultant retail products stored in modified atmosphere packages (MAP 30:70 CO2/N2) at 4 °C to detect potential differences with the MAP spoilage community described previously. The initial pH of the VP minces was 6.0–6.1, except for one mince, designated VP + AA, which had initial pH 5.8 and was found to contain ‘external’ 1.26% L-lactate and 0.24% acetate associated with a vinegar smell during storage. The rest of the VP batches contained on average 0.75% L-lactate and 0.02% acetate on day 0. After 7 days at 4 °C, L-lactate decreased by at least 3-fold in VP and over 5-fold in VP + AA vs. minor decreases in MAP. Acetate increased 2-fold in all batches. D-lactate (ca. 0.02% on day 0) increased by 4-fold in VP batches only. Lactic acid bacteria (LAB) became the dominant spoilers in all samples. Only VP allowed a delayed 10-fold growth (&gt;5.0 to 6.2 log cfu/g) of pseudomonads from day 7 to day 10 at 4 °C. Compared to VP, VP + AA and MAP retarded growth of LAB, pseudomonads, and enterobacteria by 1–2 log units, at final levels below 6.5, 4.5, and 3.0 log cfu/g, respectively. Enterococci, staphylococci, yeasts, and L. monocytogenes did not grow. Latilactobacillus sakei predominated in all spoiled VP batches (65.8% of 80 meat isolates) followed by Latilactobacillus fuchuensis (9.2%), Leuconostoc carnosum (6.6%), Carnobacterium divergens (6.6%), Latilactobacillus curvatus (5.3%), and Weissella koreensis (2.6%). VP + AA favored Latilactobacillus. Brochothrix thermosphacta was frequent in one VP batch. In conclusion, cold-stored (4 °C), minced, free-range chicken meat spoils more rapidly and offensively under VP than MAP or VP combined with acetate-containing (VP + AA) antimicrobial blends.

Prevalence and growth potential of Listeria monocytogenes in innovative, pre-packed, plant-based ready-to-eat food products on the Belgian market

In recent years, pre-packed ready-to-eat (RTE) food products on the Belgian market have shifted to a more plant-based composition due to a variety of reasons, including consumer concerns about health, animal welfare, and sustainability. However, similar to animal-based RTE foods, plant-based RTE foods can be susceptible to the presence and outgrowth of Listeria monocytogenes (L. monocytogenes). Three innovative, pre-packed, plant-based RTE food product categories on the Belgian market were identified based upon data gaps regarding the prevalence and growth potential of this pathogen. These were vegetarian and vegan deli sandwich slices (category 1), fresh-cut (mixes of) leafy vegetables (category 2), and multi-ingredient salad bowls (category 3). Reports on associated listeriosis outbreaks and recalls were collected and a comprehensive literature review on the prevalence of L. monocytogenes (i.e. detection in 25 g food) was performed. In addition, the prevalence of L. monocytogenes was also determined through an exploratory retail survey of ca. 50 different RTE products of each category. A batch was considered positive if L. monocytogenes was detected in a food item, either on the day of purchase, at the end of shelf life, or both. During the retail survey, L. monocytogenes was not detected in category 2 (0 out of 51 batches), while 1 out of 51 and 6 out of 48 batches were found positive for respectively category 1 and 3. The observed L. monocytogenes concentration did not exceed 10 CFU/g at any point in time in any batch. Furthermore, challenge tests were performed to determine the growth potential of L. monocytogenes in nine pre-packed, plant-based RTE food products (two to four different products of each category, and three different batches per product). After inoculation, products were stored for half of their shelf life at 7 °C and half of their shelf life at 9 °C (simulation of resp. retail and consumer storage). In six of the nine challenge tests executed, growth of L. monocytogenes was supported (i.e. growth potential ≥0.50 log10 CFU/g during shelf life). The highest growth potential was observed for fresh-cut iceberg lettuce (3.60 log10 CFU/g in 9 days), but a large variation regarding the growth potential of L. monocytogenes was noted both between and within the three studied pre-packed, plant-based RTE food product categories. This variation was mainly caused by differences in product composition, physicochemical product characteristics, present (competitive) microbiota such as lactic acid bacteria, applied preservation techniques, and shelf life.

Microbial Growth Dynamics in Minced Meat Enriched with Plant Powders

Plant powders with antimicrobial properties can be used in food manufacturing and must comply with the demands of consumers regarding microbiological safety, nutritional value, and sensory properties of foods. The present study aimed to assess the microbial growth inhibitory ability of different plant powders, including by-products of horticultural primary processing (e.g., pomace) in raw and cooked minced pork. The total counts of aerobic mesophilic bacteria, pseudomonads, yeasts, and moulds were studied to assess the microbial growth dynamics in meat samples. Additionally, for the plant powders, which were able to suppress the microbial growth in a total counts dynamics study, the growth potential of Listeria monocytogenes in ready-to-eat (RTE) minced meat samples was estimated by challenge testing. The results showed that the most effective combinations of plant powders in raw minced pork, in relation to the total counts of microorganisms, were 3% apple+1% onion+2% blackcurrant berries (Apple+On+BCber); 3% apple+1% garlic+2% tomato (Apple+Ga+Tom); and 3% apple+2% tomato+1% rhubarb petioles (Apple+Tom+Rhub). However, challenge tests revealed that some plant powders were unable to inhibit the growth of L. monocytogenes. The lowest L. monocytogenes growth potential (δ = 2.74 log cfu/g) was determined for cooked minced pork samples enriched with 2% rhubarb petioles, followed by Apple+On+BCber (δ = 3.63 log cfu/g) and Apple+Tom+Rhub (δ = 3.74 log cfu/g). In minced pork samples without plant additives, the L. monocytogenes growth potential was 7.30 log cfu/g. In conclusion, blends of plant powders may have good potential for developing meat products with acceptable microbiological quality.

Growth potential of Listeria monocytogenes in veal tartare.

In the present study the growth potential of Listeria monocytogenes in veal tartare was evaluated. A challenge test was performed on three tartare batches at 8°C, aiming to evaluate the growth potential of the pathogen. The data indicated the absence of a significant growth (δ<0.5 log cfu/g) during the entire period. When considering intermediate sampling times, an increase of 0.56 log cfu/g was detected after five days of storage in one of the batches. Microflora of veal tartare was dominated by lactic acid bacteria, that increased gradually during the trial, reaching counts up to 7 Log CFU/g in two of the three batches considered. Spoilage bacteria were present (especially Pseudomonas spp., yeasts and Enterobacteriaceae) but in very low counts and with a limited increase during the period considered. Finally, daily maximum tolerable L. monocytogenes counts were calculated to highlight the maximum acceptable load to avoid the overcoming of the legal limit of 100 CFU/g: a total increase of 0.95 log cfu/g in 12 days of shelf-life was estimated, obtaining a “safety initial concentration” at t0 of 10 CFU/g of the pathogen.

Growth potential of Listeria monocytogenes in cold smoked sausages with and without fermentation

Growth potential of Listeria monocytogenes in cold smoked sausages with and without fermentation

Growth Potential of Listeria monocytogenes on Refrigerated Spinach and Rocket Leaves in Modified Atmosphere Packaging.

Minimally processed ready-to-eat (RTE) vegetables are increasingly consumed for their health benefits. However, they also pose a risk of being ingested with food-borne pathogens. The present study investigated the ability of RTE spinach and rocket to support the growth of Listeria monocytogenes as previous studies provided contradicting evidence. Findings were compared to growth on iceberg lettuce that has repeatedly been shown to support growth. Products were inoculated with a three-strain mix of L. monocytogenes at 10 and 100 cfu g−1 and stored in modified atmosphere (4 kPa O2, 8 kPa CO2) at 8 °C over 7–9 days. Spinach demonstrated the highest growth potential rate of 2 to 3 log10 cfu g−1 over a 9-day period with only marginal deterioration in its visual appearance. Growth potential on rocket was around 2 log10 cfu g−1 over 9 days with considerable deterioration in visual appearance. Growth potential of iceberg lettuce was similar to that of rocket over a 7-day period. Growth curves fitted closely to a linear growth model, indicating none to limited restrictions of growth over the duration of storage. The high growth potentials of L. monocytogenes on spinach alongside the limited visual deterioration highlight the potential risks of consuming this raw RTE food product when contaminated.

Growth Potential of Listeria monocytogenes in Three Different Salmon Products.

Cold smoked salmon and sushi salmon have been implicated in outbreaks of listeriosis. We performed challenge tests and a durability study with Listeria monocytogenes on different salmon products to determine the growth potential of this important food-borne pathogen. Data from the challenge test showed a significant growth potential of L. monocytogenes on all of the tested salmon products, with faster growth in sushi salmon than in cold smoked salmon. In identical products that were naturally contaminated at low levels, the durability study did not confirm a high growth potential, possibly due to interactions with competing microflora. The injection of sodium lactate (NaL) at a high concentration (30%) into cold smoked salmon significantly reduced the growth potential of L. monocytogenes. In addition to good manufacturing practices, the injection of higher concentrations of NaL may therefore be a useful additional hurdle to prevent growth of L. monocytogenes to high numbers in the tested salmon products.

Determination of the growth potential of Listeria monocytogenes in various types of Belgian artisanal cheeses by challenge tests

Cheese potentially allowing the growth of Listeria monocytogenes must be free of the pathogen in 25 g before being put on the market, while 100 cfu/g is tolerated when the pathogen is unable to grow. Challenge tests were performed in order to assess the growth potential of L. monocytogenes in at least one batch of 32 Belgian cheese varieties from 32 factories. All varieties were grouped in four categories: unripened acid-curd cheeses, mold-ripened soft cheeses, smear-ripened soft cheeses and ripened semi-hard cheeses. Associated microflora and cheese physicochemical characteristics were also studied. A cocktail of three strains was used to inoculate cheese on the first day of shelf-life, and samples were stored until the end of shelf-life at 7–9 °C. Growth potential was considered as the difference (a) between median contamination at the end and at the beginning of the test or (b) between the highest value at the end of the test and the lowest value at its beginning. L. monocytogenes always decreased in unripened acid-curd cheeses but showed extended growth in 21 out of 25 batches of ripened soft cheese. Contrasting results were obtained for semi-hard cheeses, as important intra- and inter-batch variability was observed. For the latter, the recommended method based on medians to calculate the growth potential led to erroneous food safety considerations, and it should always be advised to focus on absolute levels.

Antimicrobial and Antioxidative Effects of Plant Powders in Raw and Cooked Minced Pork.

It is a challenge for scientists to find new plant-based food constituents simultaneously possessing antimicrobial and antioxidative properties to prolong the shelf life of meat products. In this study, various plant powders and their blends were added to minced pork to carry out a complex study of their effect on sensory characteristics, microbial growth, and lipid oxidation of the meat in raw and cooked forms during storage. Microbiological shelf life parameters were evaluated by determining the total counts of microorganisms, yeasts, and molds. The growth potential of Listeria monocytogenes was estimated by challenge testing. The impact on lipid oxidation processes was assessed using thiobarbituric acid reactive substances (TBARS) and high performance liquid chromatography (HPLC) methods. The results showed that the blend of rhubarb petioles and tomato powder added a pleasant color and a combined taste to the product, similar to the taste of salt. In raw samples, considerable microbial growth inhibition was achieved with rhubarb petioles, tomato, and their mixture. Nine treatments of cooked samples had a stronger inhibitory effect on microbial growth compared to control treatments. Among all plant powders, tomato was the most effective inhibitor of yeast and mold growth. However, the challenge test revealed that L. monocytogenes growth in cooked samples was not inhibited during shelf life. In raw samples, rhubarb roots combined with blackcurrant or chokeberry berries effectively inhibited lipid oxidation, and in cooked samples, rhubarb petioles showed a similar effect. In conclusion, it was found that powdered plant materials are well suited for use as antimicrobial and antioxidative agents in minced meat products.

Shelf life and growth potential of Listeria monocytogenes in steak tartare

The evaluation of the microbiological shelf-life under refrigeration conditions of steak tartare showed Total Viable Counts (excluding LAB) around 4 Log CFU/g at the beginning of the study, with a gradual increase reaching 7 Log CFU/g after 12 days. LAB represented the main microflora. A significant acidification was detected at the end of the shelf life. Total Volatile Basic Nitrogen concentration changed slightly during the shelf life. After an initial increase (until T5), all the colour indices were stable. The growth potential of Listeria monocytogenes was also evaluated in accordance with EURL Lm guidelines by conducting challenge tests. The growth potential calculated during the challenge test performed on three different batches indicated the absence of a significant growth (δ < 0.5 Log CFU/g). When considering intermediate sampling times, a maximum increase of 0.51 Log CFU/g was detected at T5 in one batch. Finally, daily thresholds (maximum tolerable L. monocytogenes counts) were calculated to highlight the maximum acceptable load of remaining shelf life to avoid the overcoming of the legal limit of 100 CFU/g. Considering the worst-case scenario, a total increase of 0.89 Log CFU/g in 12 days was estimated, obtaining a “safety initial concentration” of 1.11 Log CFU/g of the pathogen.

Growth Potential of Listeria monocytogenes in Chef-Crafted Ready-to-Eat Fresh Cheese-Filled Pasta Meal Stored in Modified Atmosphere Packaging

This study evaluated the growth of lactic acid bacteria (LAB) in a fresh, filled-pasta meal, stored in modified atmosphere packaging and the influence of lactic acid (LA) and pH on the growth of Listeria monocytogenes (Lm). Samples were taken from three lots manufactured by a local catering company and stored at both 6 and 14°C. LAB numbers, LA concentration, pH, and the presence of Lm were evaluated at 1, 4, 6, 8, 10, 12, and 14 days of shelf life and the undissociated LA concentration ([LA]) was calculated. The LAB maximum cell density was greater in the products stored at 14°C than those stored at 6°C (10.1 ± 1.1 versus 5.6 ± 1.5 log CFU/g) and [LA] at 14 days was 9 to 21 ppm at 6°C and 509 to 1,887 ppm at 14°C. Challenge tests were made to evaluate the interference of LAB and [LA] on Lm growth. Aliquots of the samples (25 g) were inoculated at 1 to 10 days of shelf life and incubated at 9°C for 7 days, and the difference between Lm numbers at the end and at the beginning of the test (δ) was calculated. Logistic regression was used to model the probability of growth of Lm as a function of LAB and [LA]. The products inoculated at 1 day of shelf life had δ values between 4.2 and 5.6 log CFU/g, but the growth potential was progressively reduced during the shelf life. Lm growth was never observed in the products stored at 14°C. In those stored at 6°C, it grew only in the samples with LAB <5.7 log CFU/g. LAB interaction might thus inhibit the growth of Lm in temperature-abused products and limit its growth in refrigerated products. Logistic regression estimated that the probability of Lm growth was <10% if LAB was >6.6 log CFU/g or log[LA] was >2.2 ppm. The growth or inactivation kinetic of Lm was investigated with a homogenate of three samples with LAB numbers close to the maximum population density. After an initial growth, a subsequent reduction in the number of Lm was observed. This means that the maximum numbers of Lm might not be detected at the end of the product shelf life.

Growth potential of Listeria monocytogenes in twelve different types of RTE salads: Impact of food matrix, storage temperature and storage time

Listeriosis is a food borne disease associated with high hospitalization and fatality rates; in 2014, EU member states reported 2194 cases with 98.9% hospitalization rates and 210 fatalities. Proper risk analysis and the development of effective food safety strategies critically depend on the knowledge of the growth characteristics of L. monocytogenes on the product in question. Ready-to-eat (RTE) salads present a challenge in this context due to the absence of a heat treatment step before consumption. This study provides challenge-test based data of the growth characteristics of L. monocytogenes on twelve RTE salads. The food matrix, storage time and storage temperature were factors with a significant impact on the growth of L. monocytogenes. While most tested salads permitted a significant increase of L. monocytogenes in at least one of the tested conditions, no growth was observed on celeriac, carrot and corn salad products. There was a considerable increase in growth at 8 °C compared to 5 °C. Our data indicate that the reduction of the storage temperature at retail level to 5 °C and product shelf life could help mitigate the risk of L. monocytogenes in RTE salads.

Growth potential of Listeria monocytogenes in six different RTE fruit products: impact of food matrix, storage temperature and shelf life.

We tested the growth potential of Listeria monocytogenes on six RTE fruit products at low (4°C at the factory followed by 8°C retail/home storage) and abusive (4°C followed by 12°C) storage temperatures. Sliced coconut and fresh cut cantaloupe, as well as a fruit mix containing diced pineapple, cantaloupe, apples and grapes supported the growth of L. monocytogenes with a growth potential δ>0.5 log CFU/g over six days. Mangoes, a mix of diced kiwi, cantaloupe and pineapple as well as a mix of diced pineapple, mango, grapefruit, kiwi and pomegranate did not support a growth potential that exceeded 0.5 log CFU/g over six days. The growth potential of L. monocytogenes correlated significantly with the pH; no product with a pH below 4 showed a significant growth potential of L. monocytogenes. Time after inoculation was also a significant predictor of the growth potential, while the fruit type and storage temperature were not.

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

Growth potential of Listeria monocytogenes in soft, semi-soft and semi-hard artisanal cheeses after post-processing contamination in deli retail establishments

Opportunities for post-processing contamination of cheese may occur in deli retail establishments, either during the further cheese ripening (at maximum 14 °C), during storage and display in the refrigeration cabinet (at maximum 7 °C) or during slicing. A L. monocytogenes post-processing contamination was simulated by inoculation either on the cheese slicing surface or the cheese rind of three soft cheeses (one white-molded raw cow's milk cheese, one pasteurized cow's milk cheese with spicy herbs, one washed rind pasteurized cow and sheep's milk cheese) and two semi-hard cheeses (one smear-ripened raw cow's milk cheese and one natural-ripened raw cow's milk cheese). L. monocytogenes challenge testing was performed on 3 batches of each cheese to assess the growth potential of L. monocytogenes after 14 days storage at either 7 or 14 °C. Substantial growth of L. monocytogenes (>0.5 log CFU/g) was obtained in 79.2% of all individual challenge tests (n = 178) that were performed although huge variation in growth potential was noted among the different cheese types and storage conditions. The growth potential on soft cheeses stored at 7 °C ranged from 1.8 to 4.0 log units and from 3.6 to 5.5 log units upon storage at 14 °C, whilst on semi-hard cheese, this was in general lower, and ranged from 0.1 to 1.4 log units at 7 °C and from 0.0 to 3.0 log units at 14 °C. Overall, increased outgrowth of L. monocytogenes was noted when inoculation was performed on the cheese slicing surface compared to the cheese rind. Thus if occasional post-processing contamination takes place during storage or handling of the cheese, L. monocytogenes has the potential to grow to elevated numbers throughout a reasonably expected storage period of up to 14 days notwithstanding the presence of high numbers of indigenous lactic acid bacteria in these cheeses. Also for a defined cheese type both a considerable inter-batch and intra-batch variability was sometimes noted from the replicate testing, indicating no consistent behavior of L. monocytogenes in these fermented dairy products. As such it is recommended that appropriate hygienic measures are taken to prevent post-processing contamination. Noting the growth potential, absence of L. monocytogenes in 25 g of cheese using a multiple sample subunit approach (n = 5) at the time of production is important to ensure compliance to EU legislation 2073/2005.

Growth potential of Listeria monocytogenes in artificially contaminated celery and chicken salad

In a recent outbreak of listeriosis, celery, an ingredient of chicken salad, was identified as the vehicle for contamination. Epidemiological studies showed that the contaminated celery and chicken salad were contained with very low levels of L. monocytogenes. As infectious dose of L. monocytogens is considered to be high, questions were raised about the possibility of the of L. monocytogenes growth in these products before they were consumed. In this study the growth potential of three strains of L. monocytogenes representing three major serotypes were studied as a function of three different storage temperatures (5, 10 and 25 °C) and different incubation period (30 days at 5 °C, 12 days at 10 °C and 7 days at 25 °C) in cut celery and chicken salad prepared as per the recipe of the outbreak chicken salad. The growth of all three strains in celery and in laboratory made chicken salads was comparable. At 5 °C and 10 °C all three strains grew in celery by 1–2 log within 30 and 12 days, respectively. The growth of these strains under similar conditions in laboratory made chicken salad was 5–6 logs. The growth at 25 °C increased to 4–6 logs both in celery and laboratory made chicken salad within 3–4 days. These data show that celery and chicken salad can support L. monocytogenes growth and can reach high numbers even at refrigerated temperature if stored for a long time.

Thermal Inactivation and Growth Potential of Listeria Monocytogenes in Smoked Tench.

An experimental study for the evaluation of Listeria monocytogenes inactivation during a hot smoking process in tench was performed using Listeria innocua strains. Furthermore, the survival of L. monocytogenes in smoked tench was determined after post-processing in contaminated samples, evaluating the growth potential during storage. L innocua was not detected after the smoking process. In the challenge test, the growth potential of L. monocytogenes was 5.68 log colony forming unit g–1. The results showed that hot smoking at an inner temperature around 72°C is able to eliminate the microorganism. Nevertheless, the product is able to support the growth of the pathogen if post-process contamination occurs, as the food is suitable for Listeria multiplication. Product recontamination should be prevented by means of appropriate application of hygiene measures.

Recovery and Growth Potential of Listeria monocytogenes in Temperature Abused Milkshakes Prepared from Naturally Contaminated Ice Cream Linked to a Listeriosis Outbreak.

The recovery and growth potential of Listeria monocytogenes was evaluated in three flavors of milkshakes (vanilla, strawberry, and chocolate) that were prepared from naturally contaminated ice cream linked to a listeriosis outbreak in the U.S. in 2015, and were subsequently held at room temperature for 14 h. The average lag phase duration of L. monocytogenes was 9.05 h; the average generation time was 1.67 h; and the average population level increase per sample at 14 h was 1.14 log CFU/g. Milkshake flavors did not significantly affect these parameters. The average lag phase duration of L. monocytogenes in milkshakes with initial contamination levels ≤ 3 CFU/g (9.50 h) was significantly longer (P < 0.01) than that with initial contamination levels > 3 CFU/g (8.60 h). The results highlight the value of using samples that are contaminated with very low levels of L. monocytogenes for recovery and growth evaluations. The behavior of L. monocytogenes populations in milkshakes prepared from naturally contaminated ice cream linked to the listeriosis outbreak should be taken into account when performing risk based analysis using this outbreak as a case study.