Transmission of MRSA along the meat supply chain

Methicillin-resistente Staphylococcus aureus (MRSA) zählen zu den bedeutendsten antibiotikaresistenten Pathogenen, die vor allem in Krankenhäusern aber auch außerhalb von Einrichtungen des Gesundheitswesens weit verbreitet sind. Seit einigen Jahren ist eine neue Generation von MRSA auf dem Vormarsch, die vor allem Nutztierbestände als neue Nische besiedelt. Diese sogenannten Nutztier-assoziierten MRSA wurden wiederholt bei wirtschaftlich bedeutenden Nutztieren sowie daraus gewonnenem Fleisch nachgewiesen. Im Rahmen der vorliegenden Arbeit wurde ein methodischer Ansatz verfolgt, um die Hypothese einer möglichen Übertragung von Nutztier-assoziierten MRSA entlang der Lebensmittelkette vom Tier auf dessen Fleisch zu bestätigen. Angepasst an die Unterschiede in den verfügbaren Daten wurden dafür zwei neue Konzepte erstellt. Zur Analyse der Übertragung von MRSA entlang der Schlachtkette wurde ein mathematisches Modell des Schweineschlachtprozesses entwickelt, welches dazu geeignet ist, den Verlauf der MRSA-Prävalenz entlang der Schlachtkette zu quantifizieren sowie kritische Prozessschritte für eine MRSA-Übertragung zu identifizieren. Anhand von Prävalenzdaten ist es dem Modell möglich, die durchschnittlichen MRSA-Eliminations- und Kontaminationsraten jedes einzelnen Prozessschrittes zu schätzen, die anschließend in eine Monte-Carlo-Simulation einfließen. Im Ergebnis konnte gezeigt werden, dass es generell möglich ist, die MRSA Prävalenz im Laufe des Schlachtprozesses auf ein niedriges finales Niveau zwischen 0,15 bis 1,15% zu reduzieren. Vor allem das Brühen und Abflämmen der Schlachtkörper wurden als kritische Prozesse im Hinblick auf eine MRSA-Dekontamination identifiziert. In Deutschland werden regelmäßig MRSA-Prävalenz und Typisierungsdaten auf allen Stufen der Lebensmittelkette verschiedener Nutztiere erfasst. Um die MRSA-Daten dieser Querschnittstudie hinsichtlich einer möglichen Übertragung entlang der Kette zu analysieren, wurde ein neuer statistischer Ansatz entwickelt. Hierfür wurde eine Chi-Quadrat-Statistik mit der Berechnung des Czekanowski-Ähnlichkeitsindex kombiniert, um Unterschiede in der Verteilung stammspezifischer Eigenschaften zwischen MRSA aus dem Stall, von Karkassen nach der Schlachtung und aus Fleisch im Einzelhandel zu quantifizieren. Die Methode wurde am Beispiel der Putenfleischkette implementiert und zudem bei der Analyse der Kalbfleischkette angewendet. Die durchgehend hohen Ähnlichkeitswerte zwischen den einzelnen Proben weisen auf eine mögliche Übertragung von MRSA entlang der Lebensmittelkette hin. Die erarbeiteten Methoden sind nicht spezifisch bezüglich Prozessketten und Pathogenen. Sie bieten somit einen großen Anwendungsbereich und erweitern das Methodenspektrum zur Bewertung bakterieller Übertragungswege.Methicillin resistant Staphylococcus aureus (MRSA) is one of the most important antibiotic-resistant pathogens in hospitals and the community. Recently, a new generation of MRSA, the so called livestock associated (LA) MRSA, has emerged occupying food producing animals as a new niche. LA-MRSA can be regularly isolated from economically important live-stock species including corresponding meats. The present thesis takes a methodological approach to confirm the hypothesis that LA-MRSA are transmitted along the pork, poultry and beef production chain from animals at farm to meat on consumers` table. Therefore two new concepts were developed, adapted to differing data sets. A mathematical model of the pig slaughter process was developed which simulates the change in MRSA carcass prevalence during slaughter with special emphasis on identifying critical process steps for MRSA transmission. Based on prevalences as sole input variables the model framework is able to estimate the average value range of both the MRSA elimination and contamination rate of each of the slaughter steps. These rates are then used to set up a Monte Carlo simulation of the slaughter process chain. The model concludes that regardless of the initial extent of MRSA contamination low outcome prevalences ranging between 0.15 and 1.15 % can be achieved among carcasses at the end of slaughter. Thus, the model demonstrates that the standard procedure of pig slaughtering in principle includes process steps with the capacity to limit MRSA cross contamination. Scalding and singeing were identified as critical process steps for a significant reduction of superficial MRSA contamination. In the course of the German national monitoring program for zoonotic agents MRSA prevalence and typing data are regularly collected covering the key steps of different food production chains. A new statistical approach has been proposed for analyzing this cross sectional set of MRSA data with regard to show potential farm to fork transmission. For this purpose, chi squared statistics was combined with the calculation of the Czekanowski similarity index to compare the distributions of strain specific characteristics between the samples from farm, carcasses after slaughter and meat at retail. The method was implemented on the turkey and veal production chains and the consistently high degrees of similarity which have been revealed between all sample pairs indicate MRSA transmission along the chain. As the proposed methods are not specific to process chains or pathogens they offer a broad field of application and extend the spectrum of methods for bacterial transmission assessment

Modeling the transmission of livestock associated methicillin-resistant Staphylococcus aureus along the pig slaughter line

AbstractThe study introduces a new approach for a qualitative transmission assessment of MRSA throughout the pig slaughter process. Based on prevalence data found in literature the MRSA contamination and elimination rates of each individual slaughter step were estimated. The rates were used to set up a Monte Carlo simulation for modeling the propagation of MRSA along the process chain and to quantify the impact of a variable initial prevalence on the outcome prevalence of the carcasses. Sensitivity analyses for the model as well as three different scenarios were performed to estimate the impact of cross contamination during slaughter and to determine the process stages where hygiene interventions are most effective.Regardless of the initial extent of MRSA contamination low outcome prevalences ranging between 0.15 and 1.15% were achieved among pig carcasses indicating that the pig slaughter chain generally includes process steps with the capacity to limit carcass contamination. Especially scalding and singeing can lead to a significant reduction of superficial MRSA contamination during the first half of the slaughter process. Nevertheless, scenario analyses showed that the low MRSA outcome prevalence can only be guaranteed if recontamination during the ongoing slaughter process is obviated. In order to ensure a low MRSA load on pig carcasses at the end of slaughter the abattoir should primarily concentrate on controlling the process parameters of scalding and singeing and avoiding recontamination at subsequent process steps

Identification of the source of a Listeria monocytogenes outbreak by investigational tracing

AbstractThe number of identified listeriosis outbreaks has increased since the sequence typing of Listeria monocytogenes isolates was established in Germany. Due to the nature of the disease, listeriosis outbreaks are difficult to solve. We present investigational tracing as a simple and rapid method to conduct outbreak investigations. The method was applied in 2019 to stop a prolonged listeriosis outbreak in Germany. The starting point for the investigational tracing was nine health care facilities (HCF). Single cases developed listeriosis while they were staying at the nine facilities. Data were collected from companies that delivered foods to HCF and from ready-to-eat (RTE) foods that were consumed there. Following a step-wise approach, data analysis identified similarities in the food supply of the HCF. Food data were heterogeneous and needed to be standardised. Own brands and changing article numbers were challenging aspects during the identification of manufacturers. The analysis of the delivering companies revealed no similarities. Detailed information about the consumed risk foods for Listeria contamination became available for six HCF. All facilities served a wide variety of cold cut meat products to their in-patients. Investigational tracing revealed that only meat products from one out of 29 food business operators had been consumed in all six HCF. Further activities of the authorities enabled the identification of the outbreak strain on food products and in the processing environment of this company. A product recall and the measures taken stopped the listeriosis outbreak. Thus, investigational tracing can be crucial for the clarification of listeriosis outbreaks.</jats:p

Comparison of <i>spa</i> Types, SCC<i>mec</i> Types and Antimicrobial Resistance Profiles of MRSA Isolated from Turkeys at Farm, Slaughter and from Retail Meat Indicates Transmission along the Production Chain

<div><p>The prevalence of MRSA in the turkey meat production chain in Germany was estimated within the national monitoring for zoonotic agents in 2010. In total 22/112 (19.6%) dust samples from turkey farms, 235/359 (65.5%) swabs from turkey carcasses after slaughter and 147/460 (32.0%) turkey meat samples at retail were tested positive for MRSA. The specific distributions of <i>spa</i> types, SCC<i>mec</i> types and antimicrobial resistance profiles of MRSA isolated from these three different origins were compared using chi square statistics and the proportional similarity index (Czekanowski index). No significant differences between <i>spa</i> types, SCC<i>mec</i> types and antimicrobial resistance profiles of MRSA from different steps of the German turkey meat production chain were observed using Chi-Square test statistics. The Czekanowski index which can obtain values between 0 (no similarity) and 1 (perfect agreement) was consistently high (0.79–0.86) for the distribution of <i>spa</i> types and SCC<i>mec</i> types between the different processing stages indicating high degrees of similarity. The comparison of antimicrobial resistance profiles between the different process steps revealed the lowest Czekanowski index values (0.42–0.56). However, the Czekanowski index values were substantially higher than the index when isolates from the turkey meat production chain were compared to isolates from wild boar meat (0.13–0.19), an example of a separated population of MRSA used as control group. This result indicates that the proposed statistical method is valid to detect existing differences in the distribution of the tested characteristics of MRSA. The degree of similarity in the distribution of <i>spa</i> types, SCC<i>mec</i> types and antimicrobial resistance profiles between MRSA isolates from different process stages of turkey meat production may reflect MRSA transmission along the chain.</p></div

MRSA prevalence and distribution of <i>spa</i> types, SCC<i>mec</i> types and antimicrobial resistance clusters at different steps of the German turkey meat production chain in 2010.

a<p>MRSA isolates which did not exactly correspond to the monitoring sampling plan in terms of completeness of data reporting to the national level were excluded from prevalence estimations but included in further typing and strain comparisons.</p>b<p>Not typable.</p>c<p>Resistance cluster were calculated using Ward’s minimum variance with squared Euclidean distance.</p

Similarity matrix of <i>spa</i> types, SCC<i>mec</i> types and resistance profiles of MRSA isolated from the German turkey meat production chain in the course of the national monitoring for zoonotic agents in 2010 (95% confidence intervals).

a<p>PSI: Czekanowski index or proportional similarity index.</p>b<p>CI 95%: 95% confidence interval.</p

Antimicrobial resistance of MRSA in the German turkey meat production chain.

<p>Distribution of antimicrobial resistance of MRSA strains separated into CC398 and non CC 398 strains as well as different steps of the turkey meat production chain isolated from dust samples at turkey primary production (n = 32), carcasses at slaughter (n = 248) and meat at retail (n = 241). The MRSA strains were isolated in the course of the national monitoring for zoonotic agents in Germany in 2010.</p