Slaughter pigs as carrier of Listeria monocytogenes in Germany

Listeria (L.) monocytogenes as the cause of human listeriosis is widespread in the environment and a hazard considering food safety. Almost all animal species as well as humans can be asymptomatic carriers of this bacterium. In pigs, the tonsils are identified as the organ with the highest detection rate compared to other sample matrices. We sampled 430 pigs in total in two slaughterhouses in Northwest and East Germany, two structurally different and important regions in pig production, to re-examine pigs as a possible source of Listeria-contamination of pork products. We detected a low prevalence of L. monocytogenes in tonsil samples of 1.6% (7/430) on single animal level and of 11.6% (5/43) on herd level with no significant difference between the two German regions. Apart from L. monocytogenes, the usually non-pathogenic L. innocua had a prevalence of 1.2% (5/430) on single animal level. From 200 pigs from Northwest Germany, intestinal content samples were analysed in addition to tonsil samples from the same animals, but no positive sample was found for L. monocytogenes (0.0%, 0/200), while four pigs were positive for L. innocua (2.0%, 4/200). Although the prevalence of L. monocytogenes in tonsils is low, the risk of cross-contaminating meat with the pathogen is still given

Hepatitis E virus cross-contamination on the surface of porcine livers after storage in Euro meat containers in a German pig abattoir

Hepatitis E virus (HEV) is a foodborne zoonotic pathogen and known as the causative agent of hepatitis E in humans. The specific role of porcine liver as a vehicle for human HEV infections has been highlighted in different studies. Nevertheless, gaps of knowledge still exist regarding possible HEV cross-contamination both at consumer and production level. Furthermore, people working in the food production industry, e.g. veterinarians and abattoir employees, are exposed to an increased risk of HEV infection. The aim of the present study was to investigate HEV cross-contamination on the surface of porcine liver in a German abattoir. The sample set included 250 samples of porcine liver parenchyma and the corresponding 250 superficial layer samples of the same livers, which were analyzed for the presence of HEV ribonucleic acid (RNA). Afterwards, the initial status of the tested liver parenchyma was compared with the occurrence of HEV RNA in the corresponding superficial layer. HEV RNA was detectable in 34% (85/250) of superficial layer samples, with 58% (49/85) of the samples originated from initially HEV negative livers. To our knowledge, this is the first study that provides an insight in the potential of HEV cross-contamination at abattoir level in Germany. Furthermore, it could be identified that the joint storage of livers in Euro meat containers has a significant impact on the presence of HEV RNA on the surface of porcine liver

Distribution and Characteristics of Listeria spp. in Pigs and Pork Production Chains in Germany

Listeria (L.) monocytogenes is a foodborne pathogen that can cause disease, mainly in elderly, pregnant or immunocompromised persons through consumption of contaminated food, including pork products. It is widespread in the environment and can also be found in asymptomatic carrier animals, for example, in different tissues of pigs. To learn more about their nature, 16 Listeria spp. isolates found in tonsils and intestinal content of pigs and 13 isolates from the slaughterhouse environment were characterized using next-generation sequencing (NGS). A wide distribution of clonal complexes was observed in pigs, as well as in the pork production chain, suggesting multiple sources of entry. Hypervirulent clones were found in pig tonsils, showing the potential risk of pigs as source of isolates causing human disease. The presence of closely related isolates along the production chain suggests a cross-contamination in the slaughterhouse or recontamination from the same source, strengthening the importance of efficient cleaning and disinfection procedures. The phenotypical antimicrobial resistance status of L. monocytogenes isolates was examined via broth microdilution and revealed a low resistance level. Nevertheless, genotypical resistance data suggested multiple resistances in some non-pathogenic L. innocua isolates from pig samples, which might pose a risk of spreading resistances to pathogenic species

The occurrence of hepatitis E virus in fattening pigs at the time of slaughter - An analysis of the predictive power of meat juice serology on the presence of hepatitis E virus in liver and muscle in pigs and the occurrence of possible cross-contamination at the abattoir

Die Infektion mit dem Hepatitis-E-Virus (HEV) beim Schwein ist in der Regel durch einen subklinischen Verlauf gekennzeichnet und geht ohne makroskopische Veränderungen an Organen oder dem Schlachtkörper einher. Am Schlachthof gelingt die Identifizierung HEVinfizierter Schweine daher weder im Rahmen der amtlichen Schlachttier- noch während der amtlichen Fleischuntersuchung. Da zudem kein Monitoringprogramm zur Bekämpfung von HEV beim Schwein existiert, besteht jederzeit das Risiko, dass HEV-belastete Produkte vom Schwein in die Lebensmittelkette gelangen und bei rohem beziehungsweise unzureichend gegartem Verzehr zu einer lebensmittelbedingten HEV-Infektion beim Menschen führen können. Vor diesem Hintergrund sollte im Rahmen dieser Dissertation die Vorhersagekraft der serologischen Analyse von Fleischsaft für das Vorkommen von HEV in der Leber und in der Schinkenmuskulatur von Mastschweinen untersucht werden. Als weiteres Ziel galt die Untersuchung des Risikos einer Kreuzkontamination ausgehend von HEV-positiven Schweinelebern auf HEV-negative Schweinelebern während der üblichen gemeinsamen Lagerung in Eurofleischkisten im Schlachthof. Es wurden zu diesem Zweck 250 Mastschweine in die vorliegende Studie einbezogen und zwischen August und Dezember 2018 an einem Schlachthof in Nordwestdeutschland beprobt. Dabei erfolgte die Auswahl der in der Studie involvierten Schweine nach dem Zufallsprinzip. Die Entnahme der vier Probenmatrices Zwerchfellpfeiler, Schinkenmuskulatur, Leberparenchym sowie Gewebe der Leberoberfläche je Schwein fand an fünf Schlachttagen statt, wobei die Tagesschlachtzahl bis zu 5.500 Schweine betrug. Der Nachweis von HEV-Antikörpern im Fleischsaft mittels ELISA-Technologie resultierte in einer HEV-Seroprävalenz von 62 % (155/250) bei den in dieser Studie involvierten Mastschweinen auf Einzeltierebene und in einer Seroprävalenz von 72 % (18/25) auf Herdenebene. Die im Europavergleich hohe HEV-Prävalenz in Schweinelebern (17 %; 43/250) wurde mithilfe der real-time RT-PCR analysiert, wobei für HEV-seropositive Schweine ein signifikant höheres Risiko für das Vorkommen von HEV-RNA in der Leber ermittelt werden konnte. Die Leberproben von HEV-seronegativen Schweinen erwiesen sich in dieser Studie hingegen alle als HEV-negativ, was statistisch in einem signifikant geringen Risiko für das Vorkommen von HEV-RNA in der Leber von seronegativen Schweinen zum Zeitpunkt der Schlachtung resultierte. In dem Zusammenhang konnte gezeigt werden, dass ein steigender prozentualer Wert der im ELISA gemessenen optischen Dichte (OD%) die Wahrscheinlichkeit des Vorkommens von HEV in der Leber von Mastschweinen erhöht (OR = 1,016; p < 0,001). Darüber hinaus wurden in einer weiteren Untersuchung die HEV-PCR-Ergebnisse der Oberfläche mit dem initialen HEV-Status des Parenchyms der jeweils identischen Leber verglichen, was in Deutschland erstmalig zu Erkenntnissen hinsichtlich einer potenziellen HEV-Kreuzkontamination ausgehend von Schweinelebern auf Schlachthofebene führte. Bei 23,8 % (49/207) der initial HEV-negativen Lebern konnte nach gemeinsamer Lagerung in Eurofleischkisten mit anderen Lebern HEV-RNA auf der Oberfläche detektiert werden. Der Anteil an Lebern mit einer HEV-positiven Oberfläche variierte zwischen den Eurofleischkisten stark, obwohl der initiale HEV-Status der Lebern berücksichtigt wurde und zeigt damit eine mögliche Kreuzkontamination ausgehend von HEV-positiven Lebern während der Lagerung in Kisten auf. Ein Nachweis von HEV-RNA in der Schinkenmuskulatur der hier untersuchten Schweine gelang nicht. Zusammenfassend betrachtet zeigen die Ergebnisse dieser Studie erstmals eine signifikante Vorhersagekraft der positiven HEV-Fleischsaftserologie auf das Vorkommen von HEV-RNA in Schweineleber. Zudem kann die Lagerung von Schweinelebern in Eurofleischkisten im Schlachthof zu einer HEV-positiven Leberoberfläche führen, auch bei initial HEV-negativen Lebern. HEV-seropositive Schweine beziehungsweise die Leber HEV-seropositiver Schweine stellen daher scheinbar ein potenzielles Risiko für lebensmittelbedingte HEV-Infektionen beim Menschen beziehungsweise für Kreuzkontaminationen im Schlachthof dar.Hepatitis E virus (HEV) infection in pigs is characterized by a subclinical course and is associated with no macroscopic lesions in organs or the carcass. Therefore, the identification of pigs infected by HEV is not possible either during official ante-mortem or post-mortem inspection at the abattoir. As no monitoring programme for HEV control in pigs exists, there is always the risk that HEV contaminated products from pigs enter the food chain and can lead to foodborne HEV infection in humans if consumed raw or undercooked.In this context, the aim of this doctoral thesis was to investigate the predictive power of serological analysis of meat juice for the presence of HEV in the liver and ham muscle of fattening pigs. The additional objective was to investigate the risk of cross-contamination originating from HEV positive pig livers to HEV negative pig livers during the standard joint storage in Euro meat containers at the abattoir. For this purpose, 250 fattening pigs were included in the present study and were sampled between August and December 2018 at an abattoir in northwestern Germany. Pigs involved in this study were selected randomly. Collecting of the four matrices diaphragm pillar, ham muscle, liver parenchyma and tissue of the liver surface per pig was performed on five slaughter days, with daily slaughter numbers up to 5,500 pigs. HEV antibody detection in meat juice by ELISA technology resulted in an HEV seroprevalence of 62 % (155/250) in the fattening pigs involved in this study at single animal level and a seroprevalence of 72 % (18/25) at herd level. The high HEV prevalence of porcine livers (17 %; 43/250), compared to other European countries, was analyzed by realtime RT-PCR, which revealed a significantly higher risk for the presence of HEV RNA in the liver of HEV seropositive pigs. In contrast, liver samples obtained from HEV seronegative pigs were all found to be HEV negative in this study, resulting statistically in a significantly low risk for the presence of HEV RNA in the livers of seronegative pigs at the time of slaughter. It could be demonstrated that an increasing percentage value of optical density (OD%) measured by ELISA increased the probability of HEV presence in the liver of fattening pigs (OR 1.016; p < 0.001). Furthermore, in an additional investigation, HEV PCR results of the liver surface were compared with the corresponding initial HEV status of the liver parenchyma, providing for the first time insights into potential HEV cross-contamination of pig livers at abattoir level in Germany. In 23.8 % (49/207) of initially HEV negative livers, HEV RNA was detected on the surface after joint storage in Euro meat containers with other livers. The proportion of pig livers with an HEV positive surface varied largely between the Euro meat containers, although the initial HEV status of the livers was taken into account, indicating possible crosscontamination originating from HEV positive livers during storage in Euro meat containers. HEV RNA could not be detected in ham muscle samples of the pigs analyzed in this study. In conclusion, the results of this study show for the first time a significant predictive power of positive HEV meat juice serology on the presence of HEV RNA in pig liver. In addition, storage of pig livers in Euro meat containers at the abattoir can result in an HEV positive liver surface, even in initially HEV negative livers. Therefore, HEV seropositive pigs or the livers of HEV seropositive pigs seem to pose a potential risk for foodborne HEV infections in humans respectively for cross-contamination in the abattoir

Comparative Study of Fresh and Frozen Broiler Neck Skin Sampled for Process Hygiene Purposes

The objective of the study was to determine the effect of freezing broiler neck skin samples before their microbial analysis, compared to freshly examined samples regarding total viable count (TVC) and Enterobacteriaceae count (EC). For this, 300 neck skin samples were taken at a German commercial broiler abattoir and each neck skin sample was cut into two parts. One randomly selected part underwent microbial examination after storage at 4 °C overnight; the other part was frozen at −30 °C for eight weeks before analysis in the same laboratory. Log cfu/g values of TVC and EC were separately compared between the fresh and frozen neck skin samples. A difference up to 0.5 log values was set as acceptable, i.e., fresh and frozen samples with counts that differed by this amount were considered as not different. The differences between the grouped samples of fresh and frozen broiler neck skin regarding both TVC and EC levels were less than 0.5 log values. Thus, it can be assumed that broiler neck skin samples, both fresh and frozen for eight weeks, are suitable for microbiological examination, as the TVC and EC results showed equivalence. Therefore, freezing broiler neck skin samples can be an option to maintain viable bacteria levels in broiler neck skin samples taken for microbiological examination in process control, when freezing and later examination is necessary due to insufficient laboratory capacity for the examination of fresh neck skin samples