Quantitative microbiological risk assessment for the occurrence of listeriosis in Brazil due to the consumption of milk processed by pasteurization or thermosonication.

This study aimed to estimate the risk of listeriosis from the consumption of pasteurized milk in Brazil, comparing conventional treatment with the technology of thermosonication. The Quantitative Microbiological Risk Assessment (QMRA) model was developed, covering the entire milk production chain, from milking to the moment of consumption. In general, higher risks were observed in association with higher initial concentrations of the pathogen and the vulnerable population. The highest risk predicted (3.67 × 10-5) was related to the scenario considering the initial concentration range of L. monocytogenes between 4 and 6 log CFU/mL, with conventional treatment and considering the vulnerable population, resulting in one case of listeriosis every 27,248 servings. When considering thermosonication treatment, lower risks have been predicted. The scenario analysis indicated that the steps related to storage conditions in retail and at the consumer's home (post-processing steps) are the most influential in the associated risk, in all scenarios. The predictive parameters of inactivation related to the applied treatment also have a considerable influence on the risk. The results point to the influence of the stages of the dairy production chain and the thermosonication treatment applied in the food safety of milk, subsidizing information for industrial application and for regulatory agencies.

Risk factors for listeriosis due to sausage consumption in Mexico: consumer practices, bacterial survival, and quantitative microbial risk assessment.

Listeriosis is a foodborne disease caused by Listeria monocytogenes (Lm), which represents a public health problem. Lm has been identified as an important contaminating bacterium of ready-to-eat meat products (RTEM) in Mexico. The objective was to explore the risk factors for acquiring listeriosis due to sausage consumption by defining the consumer profile, evaluating the survival of Lm in sausage (5, 10, and 25 °C for 32 days) and performing a quantitative microbiological risk assessment. The survey of 100 participants revealed that the factors compromising the safety of the RTEM by the consumer are the extension of the shelf life. Acquiring packaged RTEM was observed as a safe habit. All respondents stated that they were unaware of listeriosis, but 18% reported infections linked to RTEM, mainly sausage. The sausage supports the growth of Lm, whose population increases in congruence with temperature (25 °C > 10 °C >5 °C) and storage time (P ≤ 0.05). The increase in temperature decreases the adaptation time (Lag25 °C = 1.0 h, Lag10 °C= 92.5 h, Lag5 °C = 226.1 h) and increases the growth rate (µ25 °C = 4.43 CFU/h, µ10 °C = 0.075 CFU/h, µ5 °C = 0.0026 CFU/h) of Lm on the sausage. The risk of listeriosis due to sausage consumption increased according to the increase in temperature: 5.53 × 10-8-1.42 × 10-5 (5 °C), 0.00616-0.111 (10 °C), and 0.109-1.00 (25 °C). Consumer education in the hygienic management of RTEM and information on associated pathogens will minimize the risk of disease.

Assessment of the influence of selected stress factors on the growth and survival of Listeria monocytogenes.

BACKGROUND: Listeria monocytogenes are Gram-positive rods, which are the etiological factor of listeriosis. L. monocytogenes quickly adapts to changing environmental conditions. Since the main source of rods is food, its elimination from the production line is a priority. The study aimed to evaluate the influence of selected stress factors on the growth and survival of L. monocytogenes strains isolated from food products and clinical material. RESULTS: We distinguished fifty genetically different strains of L. monocytogenes (PFGE method). Sixty-two percent of the tested strains represented 1/2a-3a serogroup. Sixty percent of the rods possessed ten examined virulence genes (fbpA, plcA, hlyA, plcB, inlB, actA, iap, inlA, mpl, prfA). Listeria Pathogenicity Island 1 (LIPI-1) was demonstrated among 38 (76.0%) strains. Majority (92.0%) of strains (46) were sensitive to all examined antibiotics. The most effective concentration of bacteriophage (inhibiting the growth of 22 strains; 44.0%) was 5 × 108 PFU. In turn, the concentration of 8% of NaCl was enough to inhibit the growth of 31 strains (62.0%). The clinical strain tolerated the broadest pH range (3 to 10). Five strains survived the 60-min exposure to 70˚C, whereas all were alive at each time stage of the cold stress experiment. During the stress of cyclic freezing-defrosting, an increase in the number of bacteria was shown after the first cycle, and a decrease was only observed after cycle 3. The least sensitive to low nutrients content were strains isolated from frozen food. The high BHI concentration promoted the growth of all groups. CONCLUSIONS: Data on survival in stress conditions can form the basis for one of the hypotheses explaining the formation of persistent strains. Such studies are also helpful for planning appropriate hygiene strategies within the food industry.

Assessment of the molecular epidemiology and genetic multiplicity of Listeria monocytogenes recovered from ready-to-eat foods following the South African listeriosis outbreak.

Following the recent listeriosis outbreak in South Africa, this study was carried out to assess the safety level of various common ready-to-eat foods (RTE) obtained from supermarkets and grocery stores in major towns and cities within the Amathole, Chris Hani and Sarah Baartman Districts Municipalities, Eastern Cape Province, South Africa. A sum of 239 food samples was collected from these locations, and Listeria monocytogenes (Lm) was isolated in line with the recommended techniques by the International Organization for Standardization EN ISO 11290:2017 parts 1 and 2. Identification of the pathogen and detection of various associated virulence genes was done using Polymerase Chain Reaction (PCR) techniques. From the RTE food samples processed, Lm was detected in 107 (44.77%) of the samples. Russian sausage was the most contaminated (78.57%), followed by sliced polony (61.90%), muffins (58.33%), polony (52.63%), and pies (52.38%), while all vetkoek samples examined were negative for Lm. Although the prevalence of Lm in the food samples was very high, concentrations were generally < 100 CFU/g. Strains of Lm recovered from the RTE foods were predominantly epidemiological strains belonging to serotypes 1/2a, 1/2b and 4b. The prevalence of 10 virulence genes including the inlA, InlC, inlJ, plcA, hlyA, plcB, prfA, mpl, inlB, and actA were detected among Lm isolates. Most of the isolates (69.07%) demonstrated the potential for biofilm formation and were categorized as weak (14.95%), moderate (13.40%) and strong (40.72) biofilm formers. Furthermore, molecular typing revealed high levels of genetic diversity among Lm isolates. The findings of this investigation suggested that the presence of Lm in the RTE foods may constitute potential threats to the food sector and could pose public health hazards to consumers, particularly the high-risk group of the population. We, therefore, recommend that adequate food monitoring for safety and proper regulation enforcement in the food sector must be ensured to avoid any future listeriosis outbreak that could be linked to RTE foods in South Africa.

A quantitative risk assessment of Listeria monocytogenes from prevalence and concentration data: Application to a traditional ready to eat (RTE) meat product.

Ready to Eat (RTE) cooked meat products are among the most consumed RTE food subcategories in the EU/EEA. They are also associated with the highest number of identified listeriosis cases per year (>850), thus posing a public health risk especially among the susceptible population. This study estimated the risk of listeriosis from Italian head cheese (Coppa di Testa) consumption using a Quantitative Microbiological Risk Assessment (QMRA) based on data of prevalence and starting concentrations of Listeria monocytogenes in the product during a 3-year period (n = 1568). A consumer survey (n = 162) was conducted to provide information on domestic storage time and consumption habits, and storage conditions were determined from recordings of temperatures of domestic refrigerators (n = 57). A probabilistic model was designed for the evaluation of the growth of L. monocytogenes at each stage of the product pathway from production to consumption, using Monte Carlo simulations and employing the @Risk software. Risks associated to consumption of vacuum-packed and sliced-at-retail head cheese were assessed: The model predicted that the risk of listeriosis per serving of vacuum-packed product was in the 10-4 and 10-6 range (mean) for the high-risk and general populations respectively, and listeriosis cases were estimated to be greater than those due to consumption of sliced product (with risks in the range of 10-7 and 10-8). Overall, the model predicted that the mean number of listeriosis cases ranged from 0.001 to 0.24 and from 0.06 to 10 per one hundred thousand people, for the healthy and the high-risk population, respectively. Scenario analyses indicated that better control of the temperature of domestic refrigerators is effective in reducing the predicted risk of listeriosis for the longer stored vacuum-packed product by ~80 % for both the healthy and high-risk populations, whereas a shorter use-by-date of 30 days is an effective risk mitigation measure for both types of packed product. Model assumptions, as well as data gaps are discussed.

Quantitative risk assessment of Listeria monocytogenes in ready-to-eat (RTE) cooked meat products sliced at retail stores in Greece.

A quantitative microbial risk assessment (QMRA) model predicting the listeriosis risk related to the consumption of Ready- To- Eat (RTE) cooked meat products sliced at retail stores in Greece was developed. The probability of illness per serving assessed for 87 products available in the Greek market was found highly related to the nitrite concentration; products having a lower concentration showed a higher risk per serving. The predicted 95th percentiles of the annual listeriosis cases totaled 33 of which 13 cases were <65 years old and 20 cases ≥65 years old. The highest number of cases was predicted for mortadella, smoked turkey, boiled turkey and parizer, which were the most frequently consumed product categories. Two scenarios for assessing potential interventions to reduce the risk were tested: setting a use-by date of 14 days (these products have no use-by date based on current European Union legislation) and improving the temperature control during domestic storage. The two scenarios resulted in a decrease of the 95th and 99th percentiles of the total annual cases by 97% and 88%, respectively.

MALDI-ToF MS: A Rapid Methodology for Identifying and Subtyping Listeria monocytogenes.

Listeria monocytogenes is a major food-borne pathogen and causative agent of a fatal disease, listeriosis. Stringent regulatory guidelines and zero tolerance policy toward this bacterium necessitate rapid, accurate, and reliable methods of identification and subtyping. Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-ToF MS) has recently become a method of choice for routine identification of pathogens in clinical settings and has largely replaced biochemical assays. Identification relies on well-curated databases such as SARAMIS. Extensive use of SARAMIS to generate consensus mass spectra, in conjunction with statistical analysis, such as partial least square-discriminant analysis and hierarchical cluster analysis, is useful in subtyping bacteria. While MALDI-ToF MS has been extensively used for pathogen detection, its application in bacterial subtyping has been limited. The protocol describes a MALDI-ToF MS workflow as a single tool for simultaneous identification and subtyping of L. monocytogenes directly from solid culture medium.

Growth of Listeria monocytogenes in ready-to-eat "shrimp cocktail": Risk assessment and possible preventive interventions.

The present study investigated the presence, growth potential, and public health risk posed by Listeria monocytogenes in a ready-to-eat "shrimp cocktail". The pathogen was detected in 4 out of the 104 samples, and there were no counts above the enumeration limit (1 Log colony-forming unit (CFU)/g); the product was a suitable substrate for pathogen growth owing to its chemical/physical properties. A stochastic quantitative microbial risk assessment (QMRA) was performed to estimate the expected number of invasive listeriosis cases caused by the consumption of 10,000 servings of the product on the last day of its shelf life, considering a population comprising healthy consumers, those susceptible, and transplant recipients. The model predicted no cases for this scenario. Uncertainties were included by considering alternative scenarios; even when considering an increased mean bacterial concentration (up to 3-4 Log CFU/g), no cases were estimated. Following a producer's demand, the exposure assessment model was also used to estimate the probability of the product exceeding the threshold of 2 log CFU/g during the shelf life. The possibility of Listeria growth in the product could not be avoided. Therefore, a modification of the production process was tested to re-classify the product as unsuitable for Listeria growth (EC Reg. 2073/2005). The shrimps were conditioned in three different organic acid solutions comprising: acetic acid (1500 ppm) (A); benzoic acid (1500 ppm) + acetic acid (500 ppm) + lactic acid (750 ppm) (BLA); and lactic acid (4500 ppm) + sodium acetate (2500 ppm) (LSA). Testing was conducted over various treatment durations (1 day-5 days). Treatment for 2 days in the LSA solution was selected based on efficacy, the absence of consumer-perceptible sensorial modifications, and the producers' production rate requirements. The concentration of L. monocytogenes decreased when the new process was applied, which confirmed the usefulness and effectiveness of the treatment relative to the traditional process. Thus, the product obtained by the modified production process did not support the growth of L. monocytogenes.

Virulence assessment of Listeria monocytogenes grown in different foods using a Galleria mellonella model.

Various produce including cantaloupe, caramel-coated apples, and packaged salads, have been recognized in recent years as vehicles for listeriosis, a human foodborne disease caused by intracellular pathogen Listeria monocytogenes. Our knowledge regarding the role of these foods in L. monocytogenes virulence, however, is limited. Understanding their role in modulating L. monocytogenes virulence can be useful in risk assessments and for developing control measures. In this study, we employed the Galleria mellonella larvae model to evaluate virulence potential of fifteen clinical, environmental and food isolates of L. monocytogenes, related to three major outbreaks, after growth on different foods. The non-human pathogen Listeria innocua was also included in the panel. Strains were inoculated in parallel in 5ml of brain heart infusion (BHI) broth, and on the surfaces of cantaloupe and apple fragments (5g each) at about 105 colony forming units (CFU)/ml/fragment. One set of inoculated broth and food fragments was incubated at 10°C for 5 days while the second set was kept at 25°C for 3 days. L. monocytogenes cells were recovered from the fruits and BHI, washed twice, re-suspended in saline, and used to inoculate G. mellonella larvae at final concentrations of 106 and 105 CFU/larva. The larvae were incubated at 37°C and monitored for mortality (LT50-time taken to kill 50% of the larvae) and phenotypic changes over seven days. L. monocytogenes grown on cantaloupe and apple flesh surfaces resulted in higher virulence than when grown in BHI. L. monocytogenes infection at 106 CFU/larvae resulted in an average LT50 of ≤ 30, 36 and 47 hours on cantaloupe, apples and BHI, respectively. These results represent a 2.5-4-fold increased mortality compared with an LT50 ≥120 hours in larvae infected with the same doses of L. innocua grown in corresponding matrices. Similar trends were also recorded with doses of about 105 CFU /larvae.

Toward a Better Understanding of Listeriosis Risk among Older Adults in the United States: Characterizing Dietary Patterns and the Sociodemographic and Economic Attributes of Consumers with These Patterns.

ABSTRACT: Older adults are at higher risk of invasive listeriosis compared with the general population. Some foods are more likely than others to be contaminated with or to contain high levels of Listeria monocytogenes. The objectives of this study were to (i) determine dietary consumption patterns among older adults in the United States; (ii) evaluate sociodemographic and economic characteristics of older adults associated with each pattern; (iii) determine intake of foods associated with larger relative risk of listeriosis within these patterns; and (iv) rank these patterns based on risk. Data related to older adults (age 60 and older) participating in the cross-sectional National Health and Nutrition Examination Surveys (NHANES) 2009 to 2010, 2011 to 2012, and 2013 to 2014 (n = 4,967) were included in these analyses. Cluster analysis was used to define dietary patterns based on 24-h dietary recalls from day 1 and day 2. Mean intake of foods associated with higher risk of listeriosis was examined within each pattern, and analysis of variance with Dunnett's method of adjustment was used to evaluate significant differences in mean intake of foods. Patterns were ranked based on relative risk of listeriosis, using outbreak illness attribution data. Five distinct dietary patterns were identified. Patterns ranked at highest relative risk of listeriosis, based on U.S. outbreak illness attribution data, were characterized by relatively higher intakes of fruits, vegetables, and cheeses (∼13% respondents) or cereal, milk, and yogurt (∼14% respondents). Individuals consuming these dietary patterns differed in sex, race, food security, self-rated diet quality, and self-rated health. Cluster analysis, despite methodological limitations, provides new information on consumption, sociodemographic, and economic characteristics of subgroups within susceptible populations, which may be used to target educational messages.

Assessment of memory formation by metabolically engineered antigen-specific CD8 T cells.

The formation of memory CD8+ T cells is crucial for host protection upon reencounter of the same pathogen. Moreover, long-lasting anti-tumoral effects of immunomodulatory drugs largely depend on the induction of immunological memory. While the transcriptional processes behind memory T cell differentiation have been described in detail, it is only recently becoming clear that memory T cell formation and maintenance are tightly controlled by specific metabolic pathways. Therefore, metabolic engineering of CD8+ T cells in order to promote their memory formation represents a valuable strategy to improve vaccination efficacy and cancer immunotherapy. Here, we describe several mouse in vitro and in vivo assays that can be used to evaluate whether a specific metabolic pathway is involved in memory CD8+ T cell differentiation. To this end, a metabolic process can be tested by either genetic deletion or pharmaceutical inhibition/activation of the key enzyme involved. The in vitro assays might allow for rapid screening of multiple candidate pathways, while the in vivo assays are required to reliably determine the quality and functionality of the generated memory CD8+ T cells.

An Assessment of Listeriosis Risk Associated with a Contaminated Production Lot of Frozen Vegetables Consumed under Alternative Consumer Handling Scenarios.

Frozen foods do not support the growth of Listeria monocytogenes (LM) and should be handled appropriately for safety. However, consumer trends regarding preparation of some frozen foods may contribute to the risk of foodborne listeriosis, specifically when cooking instructions are not followed and frozen products are instead added directly to smoothies or salads. A quantitative microbial risk assessment model FFLLoRA (Frozen Food Listeria Lot Risk Assessment) was developed to assess the lot-level listeriosis risk due to LM contamination in frozen vegetables consumed as a ready-to-eat food. The model was designed to estimate listeriosis risk per serving and the number of illnesses per production lot of frozen vegetables contaminated with LM, considering individual facility factors such as lot size, prevalence of LM contamination, and consumer handling prior to consumption. A production lot of 1 million packages with 10 servings each was assumed. When at least half of the servings were cooked prior to consumption, the median risk of invasive listeriosis per serving in both the general and susceptible population was <1.0 × 10-16 with the median (5th, 95th percentiles) predicted number of illnesses per lot as 0 (0, 0) and 0 (0, 1) under the exponential and Weibull-gamma dose-response functions, respectively. In scenarios in which all servings are consumed as ready-to-eat, the median predicted risk per serving was 1.8 × 10-13 and 7.8 × 10-12 in the general and susceptible populations, respectively. The median (5th, 95th percentile) number of illnesses was 0 (0, 0) and 0 (0, 6) for the exponential and Weibull-Gamma models, respectively. Classification tree analysis highlighted initial concentration of LM in the lot, temperature at which the product is thawed, and whether a serving is cooked as main predictors for illness from a lot. Overall, the FFLLoRA provides frozen food manufacturers with a tool to assess LM contamination and consumer behavior when managing rare and/or minimal contamination events in frozen foods.

Prevalence, virulence characterization, and genetic relatedness of Listeria monocytogenes isolated from chicken retail points and poultry slaughterhouses in Turkey.

Listeria monocytogenes is one of the most important foodborne pathogens and is a causal agent of listeriosis in humans and animals. The aim of this study was to determine the prevalence, serogroups, antibiotic susceptibility, virulence factor genes, and genetic relatedness of L. monocytogenes strains isolated from 500 poultry samples in Turkey. The isolation sources of 103 L. monocytogenes strains were retail markets (n = 100) and slaughterhouses (n = 3). L. monocytogenes strains were identified as serogroups 1/2a-3a (75.7%, lineage I), 1/2c-3c (14.56%, lineage I), 1/2b-3b-7 (5.82%, lineage II), 4a-4c (2.91%, lineage III), and 4b-4d-4e (0.97%, lineage III). Most of the L. monocytogenes strains (93.2%) were susceptible to the antibiotics tested. PCR analysis indicated that the majority of the strains (95% to 100%) contained most of the virulence genes (hylA, plcA, plcB, prfA, mpl, actA, dltA, fri, flaA inlA, inlC, and inlJ). Pulsed-field gel electrophoresis (PFGE) demonstrated that there were 18 pulsotypes grouped at a similarity of > 90% among the strains. These results indicate that it is necessary to prevent the presence of L. monocytogenes in the poultry-processing environments to help prevent outbreaks of listeriosis and protect public health.

Listeria monocytogenes risk assessment on cold smoked and salt-cured fishery products in Finland - A repeated exposure model.

Listeria monocytogenes causes severe consequences especially for persons belonging to risk groups. Finland is among the countries with highest number of listeriosis cases in the European Union. Although most reported cases appear to be sporadic and the maximum bacterial concentration of 100 cfu/g is not usually exceeded at retail, cold smoked and salt-cured fish products have been noted as those products with great risk especially for the elderly. In order to investigate the listeriosis risk more carefully, an exposure assessment was developed, and laboratory results for cold smoked and salt-cured salmon products were exploited. L. monocytogenes exposure was modeled for consumers in two age groups, the elderly population as a risk group and the working-age population as a reference. Incidence was assessed by estimating bacterial growth in the food products at three temperatures. Bayesian estimation of the risk was based on bacterial occurrence and product consumption data and epidemiological population data. The model builds on a two-state Markov chain describing repeated consumption on consecutive days. The cumulative exposure is probabilistically governed by the daily decreasing likelihood of continued consumption and the increasing bacterial concentrations due to growth. The population risk was then predicted with a Poisson distribution accounting for the daily probabilities of purchasing a contaminated product and the cumulative total probability of infection from its use. According to the model presented in this article, elderly Finns are at a greater risk of acquiring listeriosis than healthy adults. The risk for the elderly does not fully diminish even if the products have been stored at the recommended temperature (between 0 and 3 °C). It can be concluded that the stage after retail, i.e. food handling and storage by consumer or professional kitchens, is essential to protection against listeriosis. The estimation model provides means for assessing the joint impacts of these effects.

Assessment of the bioprotective potential of lactic acid bacteria against Listeria monocytogenes on vacuum-packed cold-smoked salmon stored at 8 °C.

Smoked salmon is a highly appreciated delicatessen product. Nevertheless, this ready-to-eat (RTE) product is considered at risk for Listeria monocytogenes, due to both the prevalence and growth potential of this bacteria on the product. Biopreservation may be considered a mild and natural effective strategy for minimizing this risk. In this study, we evaluated the following three potential bioprotective lactic acid bacterial strains against L. monocytogenes in three smoked salmon types with different physicochemical characteristics, primarily fat, moisture, phenol and acid acetic content: two bacteriocin-like producers that were isolated from smoked salmon and identified as Lactobacillus curvatus and Carnobacterium maltaromaticum and a recognized bioprotective bacteriocin producer from meat origin, Lactobacillus sakei CTC494. L. sakei CTC494 inhibited the growth of L. monocytogenes after 21 days of storage at 8 °C in all the products tested, whereas L. curvatus CTC1742 only limited the growth of the pathogen (<2 log increase). The effectiveness of C. maltaromaticum CTC1741 was dependent on the product type; this strain limited the growth of the pathogen in only one smoked salmon type. These results suggest that the meat-borne starter culture, L. sakei CTC494, may potentially be used as a bioprotective culture to improve the food safety of cold-smoked salmon.

Quantitative risk assessment of Listeria monocytogenes in bulk cooked meat from production to consumption in China: a Bayesian approach.

BACKGROUND: To estimate the public health risk related to cooked meat in bulk products contaminated with Listeria monocytogenes, a generic Bayesian network (BN) risk-assessment model was developed to simulate influencing factors and processes of products from the industry level to the consumer level. To quantify the model, parameter values of prior distributions were acquired from the literature, websites, and expert opinions. Using the Markov chain Monte Carlo (MCMC) simulation approach, posterior probability distributions were calculated according to the incorporated evidence, which allowed us to predict various risks affected by processing variability from production to consumption. RESULTS: The average risks of listeriosis from consuming cooked meat in bulk products are 8.40 × 10-7 , 2.58 × 10-8 , 8.24 × 10-7 , and 1.05 × 10-6 per meal for children, young people, elderly people, and pregnant women, respectively. The estimated mean number of listeriosis cases is 5 per 100 000 people per year in China. CONCLUSION: Although only a conceptual BN model is given, it manifests the principles and characteristics of mathematical methods. The BN model can also provide significant benefits for quantitative risk assessment by incorporating all available data and by updating beliefs. © 2018 Society of Chemical Industry.

Confirmation and Identification of Listeria monocytogenes, Listeria spp. and Other Gram-Positive Organisms by the Bruker MALDI Biotyper Method: Collaborative Study, First Action 2017.10.

The Bruker MALDI Biotyper® method utilizes matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) MS for the rapid and accurate confirmation and identification of Gram-positive bacteria from select media types. This alternative method was evaluated using nonselective and selective agar plates to identify and confirm Listeria monocytogenes, Listeria species, and select Gram-positive bacteria. Results obtained by the Bruker MALDI Biotyper were compared with the traditional biochemical methods as prescribed in the appropriate reference method standards. Sixteen collaborators from 16 different laboratories located within the European Union participated in the collaborative study. A total of 36 blind-coded isolates were evaluated by each collaborator. In each set of 36 organisms, there were 16 L. monocytogenes strains, 12 non-monocytogenes Listeria species strains, and 8 additional Gram-positive exclusivity strains. After testing was completed, the total percentage of correct identifications (to both genus and species level) and confirmation from each agar type for each strain was determined at a percentage of 99.9% to the genus level and 98.8% to the species level. The results indicated that the alternative method produced equivalent results when compared with the confirmatory procedures specified by each reference method.

Romer Labs RapidChek®Listeria monocytogenes Test System for the Detection of L. monocytogenes on Selected Foods and Environmental Surfaces.

The Romer Labs RapidChek® Listeria monocytogenes test system (Performance Tested Method 011805) was validated against the U.S. Department of Agriculture-Food Safety and Inspection Service Microbiology Laboratory Guidebook (USDA-FSIS/MLG), U.S. Food and Drug Association Bacteriological Analytical Manual (FDA/BAM), and AOAC Official Methods of Analysis (AOAC/OMA) cultural reference methods for the detection of L. monocytogenes on selected foods including hot dogs, frozen cooked breaded chicken, frozen cooked shrimp, cured ham, and ice cream, and environmental surfaces including stainless steel and plastic in an unpaired study design. The RapidChek method uses a proprietary enrichment media system, a 44-48 h enrichment at 30 ± 1°C, and detects L. monocytogenes on an immunochromatographic lateral flow device within 10 min. Different L. monocytogenes strains were used to spike each of the matrixes. Samples were confirmed based on the reference method confirmations and an alternate confirmation method. A total of 140 low-level spiked samples were tested by the RapidChek method after enrichment for 44-48 h in parallel with the cultural reference method. There were 88 RapidChek presumptive positives. One of the presumptive positives was not confirmed culturally. Additionally, one of the culturally confirmed samples did not exhibit a presumptive positive. No difference between the alternate confirmation method and reference confirmation method was observed. The respective cultural reference methods (USDA-FSIS/MLG, FDA/BAM, and AOAC/OMA) produced a total of 63 confirmed positive results. Nonspiked samples from all foods were reported as negative for L. monocytogenes by all methods. Probability of detection analysis demonstrated no significant differences in the number of positive samples detected by the RapidChek method and the respective cultural reference method.