Retrospective analysis of a listeria monocytogenes contamination episode in raw milk goat cheese using quantitative microbial risk assessment tools

in Journal of Food Protection (2012), 75(12), 2122-2135

In 2005, the Belgian authorities reported a Listeria monocytogenes contamination episode in cheese made from raw goat's milk. The presence of an asymptomatic shedder goat in the herd caused this ... [more ▼]

In 2005, the Belgian authorities reported a Listeria monocytogenes contamination episode in cheese made from raw goat's milk. The presence of an asymptomatic shedder goat in the herd caused this contamination. On the basis of data collected at the time of the episode, a retrospective study was performed using an exposure assessment model covering the production chain from the milking of goats up to delivery of cheese to the market. Predictive microbiology models were used to simulate the growth of L. monocytogenes during the cheese process in relation with temperature, pH, and water activity. The model showed significant growth of L. monocytogenes during chilling and storage of the milk collected the day before the cheese production (median increase of 2.2 log CFU/ml) and during the addition of starter and rennet to milk (median increase of 1.2 log CFU/ml). The L. monocytogenes concentration in the fresh unripened cheese was estimated to be 3.8 log CFU/g (median). This result is consistent with the number of L. monocytogenes in the fresh cheese (3.6 log CFU/g) reported during the cheese contamination episode. A variance-based method sensitivity analysis identified the most important factors impacting the cheese contamination, and a scenario analysis then evaluated several options for risk mitigation. Thus, by using quantitative microbial risk assessment tools, this study provides reliable information to identify and control critical steps in a local production chain of cheese made from raw goat's milk. © International Association for Food Protection. [less ▲]

Case study of contamination by Listeria monocytogenes in raw goat milk cheese: development of a quantitative risk assessment model of the production chain

Conference (2011, August 03)

Introduction: Quantitative Risk assessment could be applied in industries as a tool to control and manage the safety of food products. Purpose: A contamination by Listeria monocytogenes of cheeses made ... [more ▼]

Introduction: Quantitative Risk assessment could be applied in industries as a tool to control and manage the safety of food products. Purpose: A contamination by Listeria monocytogenes of cheeses made from raw milk was reported by the Belgian food agency. This contamination was caused by the presence of an asymptomatic “shedder” goat in the herd. With field and laboratory collected data, a quantitative risk assessment model of the production chain was developed. Methods: A modular risk model was built to simulate the food production pathway covering the milking of goats until the final product for the customers. A dynamic square root model was used to predict the growth rate in relation with the temperature, the pH and the water activity along the production chain with predictive microbiology modules. Results: The shedder goat was identified from the herd and milk samples were taken from the two different parts of the mammary gland with 2.6 log cfu (colonies forming units) Listeria monocytogenes/ml for the right part and absence in 25 ml for the left part of the mammary gland. Numbering of Listeria monocytogenes was carried out on the final products with 3.6 log cfu/g in the fresh not ripened cheeses. The modular risk assessment shows a significant growth of Listeria monocytogenes during chilling and storage of the milk collected the day before the cheese production (increase of 0.6 log cfu/ml) and during adjunction of ferment and rennet to milk (increase of 0.8 log cfu/ml). The model confirms the results obtained in the final products. Significance: The modular risk model gives valuable informations to identify and to control critical steps in the food production chain of goat cheese made from raw milk. Only one shedder goat can cause a high risk to become ill for the consumers of contaminated products. [less ▲]

Assessing interventions by quantitative risk assessment tools to reduce the risk of human salmonellosis from fresh pork meat in Belgium.

in Journal of Food Protection (2009), 72

Salmonella dans la filière porcine : de l'abattoir au consommateur

Article for general public (2008)

Suite aux accords internationaux et à la modification de la législation européenne, l’analyse de risque est devenue une démarche systématique pour la maîtrise de la sécurité de la chaîne alimentaire ... [more ▼]

Suite aux accords internationaux et à la modification de la législation européenne, l’analyse de risque est devenue une démarche systématique pour la maîtrise de la sécurité de la chaîne alimentaire. L’analyse de risque permet de donner des réponses concrètes aux responsables de la santé, aux vétérinaires et aux industriels. Cette discipline permet de déterminer le risque pour une population donnée face à un danger, d’estimer le nombre de cas liés suite à l’ingestion d’une denrée contaminée, de simuler les conséquences d’un accident dans la chaîne alimentaire et de présenter les mesures de prévention efficaces. Elle permet également de proposer des scénarii possibles afin de réduire le nombre de cas et les coûts associés, d’évaluer l’effet de l’implémentation de mesures de gestion comme des critères de performance (par exemple des niveaux admissibles de contamination microbienne) ou des critères de traitement (par exemple une durée ou une température à une étape donnée), etc. L’analyse de risque peut être un guide quantitatif utile pour les prises de décision si elle s'appuie sur des études scientifiques solides et si elle est complétée par des décisions industrielles, sociales et politiques qui prennent en compte les limites de cette méthode. Actuellement, le Département des Sciences des Denrées alimentaires de la Faculté Vétérinaire de l’Université de Liège associés avec d’autres partenaires réalisent une évaluation quantitative de risque concernant Salmonella dans la filière porcine (projet METZOON). Le modèle développé simule la contamination par Salmonella de l’ensemble de la filière à partir de l’élevage de porc jusqu’à la consommation de la viande par la population. Le modèle fait appel aux résultats des plans de surveillance de l’AFSCA et à l’ensemble des études réalisées en Belgique sur les salmonelles dans la filière porcine. Plusieurs industriels ont également collaboré à cette étude. Le but est d’identifier les actions ayant le plus d’efficacité pour réduire la contamination de la chaîne alimentaire. En conclusion, le nombre de salmonelloses humaines a diminué ces dernières années en Belgique. L’implémentation des méthodes HACCP et des bonnes pratiques d’hygiène dans l’industrie, une meilleure surveillance des aliments par les autorités publiques, les campagnes de vaccination des poules pondeuses en production primaire sont les raisons essentielles de la diminution. Mais l’ensemble des acteurs de la filière doivent être conscients de leur responsabilité dans le but d’obtenir une viande indemne de salmonelles. Les bonnes pratiques de fabrication doivent être respectées tout au long de la chaîne de production, en accord avec les principes HACCP, avec des contrôles fréquents sur tous les points critiques. Une traçabilité complète de l’origine de la viande ou des produits de viande est nécessaire pour permettre aux autorités publiques et aux épidémiologistes d’établir l’origine d’épidémies et ainsi réagir au plus vite. Ce n’est qu’avec une collaboration continue de tous les acteurs que nous pourrons produire une viande sans salmonelles. [less ▲]

L'évaluation quantitative du risque microbiologique: revue de trois modèles liés à Salmonella dans les aliments.

in Annales de Médecine Vétérinaire (2008), 152

Following international agreements and european legislation, risk analysis has become a systematic approach to control the food chain safety. The microbial risks in the food chain and their consequences ... [more ▼]

Following international agreements and european legislation, risk analysis has become a systematic approach to control the food chain safety. The microbial risks in the food chain and their consequences for public health can be assessed and managed more effectively. This paper gives a general description of the risk analysis principles based on the Codex Alimentarius commission. This work highlights the advantages and disadvantages of risk analysis and also treats the problems to achieve a complete “farm to fork” model. Salmonella in different food types is taken as an example to illustrate quantitative risk assessment. Two models concerning eggs and broiler chickens developed by the World Health Organization/Food and Agriculture Organization consortium and a third model concerning pigs developed by the Veterinary Laboratories Agency of the United Kingdom are described. An analysis of the methods used for the construction of these two models is also presented. The interest of these three models is that they also include risk management options to limit the spread of food-borne infections. They also describe the final risk for a population following consumption of foodstuffs. These models are valuable tools for health officials but also for feed industry. [less ▲]

Risk factors for Salmonella and hygiene indicators in the 10 largest Belgian pig slaughterhouses.

in Journal of Food Protection (2008), 77

A survey was conducted to collect data on Salmonella prevalence, Escherichia coli counts (ECCs), and aerobic bacteria colony counts (ACCs) on pig carcasses after chilling at the 10 largest Belgian pig ... [more ▼]

A survey was conducted to collect data on Salmonella prevalence, Escherichia coli counts (ECCs), and aerobic bacteria colony counts (ACCs) on pig carcasses after chilling at the 10 largest Belgian pig slaughterhouses during 2000 through 2004. Potential risk factors of contamination associated with production parameters, technical descriptions of the installations, and cleaning and disinfection methods were assessed during investigations in the slaughterhouses. These variables were used first in a univariate analysis and then were extended to a multivariate analysis with a logistic mixed regression model for Salmonella and a linear mixed model for ECCs and ACCs with slaughterhouses as the random effect. The results indicated high variability concerning Salmonella contamination among the 10 slaughterhouses, with prevalence ranging from 2.6 to 34.3% according to the area of origin. The median ECC and median ACC ranged from 0.43 to 1.11 log CFU/cm2 and from 2.37 to 3.65 log CFU/cm2, respectively. The results of the logistic and linear regressions revealed that some working practices such as scalding with steam, second flaming after polishing, and complete cleaning and disinfection of the splitting machine several times a day were beneficial for reducing Salmonella prevalence, ECCs, and ACCs. Changing the carcass hooks just before chilling, using water as the cleaning method, and a higher frequency of disinfection of the lairage seemed to be protective against E. coli in the multivariate mixed linear model. The monitoring of critical points, slaughterhouse equipment, good slaughtering practices, and effective washing and disinfection are the keys to obtaining good microbiological results. [less ▲]

Use of a serological approach for prediction of Salmonella status in an integrated pig production system

in International Journal of Food Microbiology (2006), 108(2), 246-254

Relevance of a Salmonella serological detection technique was studied from complete results obtained from 9 pigs fattening units. Feces and overshoes were sampled at different periods after starting ... [more ▼]

Relevance of a Salmonella serological detection technique was studied from complete results obtained from 9 pigs fattening units. Feces and overshoes were sampled at different periods after starting fattening (2, 3 and 4 months) while caecal contents were taken on the slaughter line. The bacteriological technique used was based on a Diasalm enrichment and a commercial test was used for serology on an average of ten animals per batch. The aim of this work was to establish a correlation between serological results obtained at slaughter (10 samples/batch) and bacteriological results. In this context, two types of logistic regression models were tested by considering alternatively serology and Salmonella detection in caecal contents as the dependent variables. Firstly, beside the fact that all logistic regression models show weak correlations, the first finding was that positive results in overshoes taken at 2 and 3 months are slightly correlated with serological status of herds (odds-ratios of 4.96 and 2.55). Secondly, when batches were characterized as positive on the basis of serological results, the probability of Salmonella recovery in caecal contents was higher than when the batches were considered as negative (odds-ratios comprised between 4.36 and 5.81). A major conclusion is that serology can be used to follow the improvement of an integrated pig production system, but is not the unique solution for assessing risk of Salmonella shedding from specific herds. (c) 2006 Elsevier B.V. All rights reserved. [less ▲]

Pork quality as related to halothane genotype and slaughter conditions in a belgian study

in Proceedings of the 50th International Congress of Meat Science and Technology (2004, August)

The objectives of this study were to evaluate technological and organoleptic properties of pork meat representative of different Belgian production systems and to determine the contribution of significant ... [more ▼]

The objectives of this study were to evaluate technological and organoleptic properties of pork meat representative of different Belgian production systems and to determine the contribution of significant factors to meat quality variability, in particular the halothane genotype, fasting time, lairage time and slaughtering plant. A total of 521 pigs were used in five Belgian commercial slaughtering plants over a 1 ½ year period. 79% of pigs belonged to four different quality production systems. The remaining 21% were randomly sampled in standard production. The lairage time (LT) was measured at slaughter. In the slaughterline, the entire intestinal tractus (OW) and the carcass (HCW) were weighed, the pH1 and electrical conductivity (PQM1) were measured 45 min post mortem in the longissimus dorsi muscle. One 2.5 cm thick cut of this muscle was removed 24h post mortem for further measurements in the lab : ultimate pH (pHu), ultimate electrical conductivity (PQMu), color (CIE L*a*b*), drip loss (DL), cooking loss (CL) and tenderness (WBPSF). The halothane genotype (CC, CT and TT for homozygote negative, heterozygote negative and homozygote positive for the RYR1 gene mutation respectively). The data were analyzed using SAS and the General Linear Model (GLM) SAS procedure was used in order to estimate the influence of halothane genotype, LT and slaughterhouse on the variability of pH1, PQM1, pHu, PQMu, drip loss, cooking loss, CIE Lab and WBPSF. The relative weight of OW on HCW was included in the models as covariate and used as inverse indicator of the fasting time. Least Squares Means (LSM) were computed for significant effect in the models and compared pairwise by the Student’s t-test. A large variation was observed for the meat quality parameters, in particular for pH1 (from 5.30 to 6.85), DL (from 1.2 to 11.4%) and CIE L* (from 41.6 to 66.4%). The lowest values for pH1 and highest values for DL or CIE L* indicated the presence of pale, soft, exudative meat. For all parameters –except for the pHu, CL and WBPSF– a moderate to great part of variation was explained by the GLM models (R² = 0.22-0.56). The halothane genotype effect was highly significant (p<0.001) on most meat quality traits : pH1, PQM1, PQMu and color parameters (CIE Lab) but not significant on pHu and CL. The LT had a highly significant influence only on PQMu, CIE b and DL. There was a highly significant effect (p<0.01) of the slaughtering plant on pH1, PQM1, PQMu and color parameters (CIE Lab) and a significant influence (p<0.01) on the variability of DL and CL. By contrast, the fasting time had no effect on most meat quality parameters except on DL (p<0.01) and CL (p<0.001). As indicated by the regression coefficient, an increase of OW/hot HCW seems to be related to an increase of DL (p<0.01) or CL (p<0.001). From the halothane genotype Least Squares Means and their standard errors, it appeared that meat quality was negatively affected by the presence of the RYR1 mutation. DL differed significantly (p<0.05) between genotypes with the TT pigs having the highest DL (6.8%) while that of the CC (5.5%) was the lowest and that of CT intermediate (6.1%). CL was also significantly higher (p<0.05) in TT pigs indicating lower water holding capacity. Significant differences between CC and TT genotypes (p< 0.05) were observed in terms of pH1 (6.12 vs 5.69), PQM1 (4.9 vs 6.4) and PQMu (9.7 vs 12.7). The CIE L and b values (56.9% and 16.6) were significantly higher (p<0.05) in the TT group comparatively to CC (55.0% and 15.8%) or CT pigs (54.6% and 15.4). The higher L value of the TT genotypes indicated paler meat. The WBPSF was the lowest for CT pigs with no significant difference observed between the CC and TT genotypes. A significant effect (p<0.05) of the abattoir was observed for all meat quality parameters. Although it would be necessary to determine the reasons for abattoirs differences, the small and old structure of one of the abattoirs and the lack of training of the staff could partially explain the results. Further research is needed to evaluate the interaction terms and to identify slaughtering factors which could explain slaughterhouse differences in terms of meat quality. [less ▲]

Comparaison des analyses sérologiques et bactériologiques de détection des salmonelles dans le suivi sanitaire d'exploitations porcines

in 36èmes Journées de la Recherche Porcine (2004)

The significance of a Salmonella serological technique has been evaluated in 91 batches from 9 pigs fattening herds. Samples for bacteriology (method based on motility of Salmonella in semi-solid medium ... [more ▼]

The significance of a Salmonella serological technique has been evaluated in 91 batches from 9 pigs fattening herds. Samples for bacteriology (method based on motility of Salmonella in semi-solid medium) were taken at different steps during fattening: 2, 3 and 4 months after the beginning of the fattening period. The serological test (Salmotype Pig-LPSElisa) has been applied on meat juice obtained after thawing of diaphragm meat cuts taken on the slaughter line. The performances of the serological method were evaluated by choosing microbiological method as reference. Correlations were practiced by comparing results of optical densities of samples with cut-off values corresponding to 4 different antibody concentrations. Forty-eight different possibilities have thus been created depending on the percentage of positive samples above the cut-off value and in function of arithmetic and geometric means. The results have shown that negative predictive values ranged from 52.8 and 100 % and that the relative sensitivity varied between 4.5 and 100 %. One classification model appeared better than the others due to maximization of Kappa, negative predictive and relative sensitivity values: batch considered positive when at least 50 % of samples were characterized by an optical density higher than OD20% (optical density corresponding to an antibody concentration of 20 %). The present experiment showed the importance of good classification of individual serological results in order to strengthen the on-farm bacteriological surveillance of herds. [less ▲]

Stratégies de prévention et de surveillance de Salmonella dans la filière porcine : 1. guide destiné aux laboratoires et aux personnes en charge des prélèvements.

Book published by Les éditions de l'Université de Liège (2003)

Ce guide s’inscrit dans le cadre d’un projet de recherche co-financé par le Ministère de l’Agriculture de la Région Wallonne et le Ministère fédéral des Classes Moyennes et de l’Agriculture et intitulé « ... [more ▼]

Ce guide s’inscrit dans le cadre d’un projet de recherche co-financé par le Ministère de l’Agriculture de la Région Wallonne et le Ministère fédéral des Classes Moyennes et de l’Agriculture et intitulé « Recherche d’une méthodologie pour la mise en place et la surveillance d’une filière intégrée de production de viande porcine Salmonella-free ». Ce projet, d’une durée de quatre ans, a débuté en février 1999. Il est destiné à sensibiliser les différents acteurs de la filière porcine sur les risques liés aux salmonelles aussi bien pour les animaux que pour les humains. Il met l’accent sur l’importance d’une bonne hygiène d’abattage et de transformation de la viande, mais aussi et surtout sur le respect des règles d’hygiène élémentaires relatives à l’élevage et à l’engraissement. L’objectif est, avant tout, de donner, aux différents maillons de la chaîne de production, des recommandations à suivre pour tendre vers une production de viande porcine indemne de salmonelles. Il s’agit donc de mesures propres à la lutte contre Salmonella dans la filière porcine, complétant les réglementations en vigueur. D’autre part, un second guide a été élaboré. Il traite des plans d’échantillonnage, des techniques de prélèvement des échantillons en exploitation et à l’abattoir, des méthodes de détection ainsi que des méthodes de caractérisation des souches de salmonelles. Il s’adresse donc davantage aux responsables des contrôles et aux laboratoires de surveillance. De ce fait, le présent guide se contente de citer les méthodes de surveillance propres à chaque étude en renvoyant au guide technique. [less ▲]