Slaughter pigs as carrier of Listeria monocytogenes in Germany

Abstract

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.

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

“…Sixteen isolates of Listeria spp. (seven L. monocytogenes and nine L. innocua ) used in this study were found in porcine samples; their distribution and prevalence in pigs were reported by Oswaldi et al [ 18 ]. Two L. monocytogenes and five L. innocua isolates originated from slaughterhouse A, taken on sampling dates 1 to 4, whereas the remaining five L. monocytogenes and four L. innocua isolates came from slaughterhouse B on sampling dates 5 and 6.…”

“…The isolates were recovered by sampling 430 fattening pigs and the slaughterhouse environment in two industrial high-capacity pig slaughterhouses in Germany, as described by Oswaldi et al [ 18 ], later referred to as slaughterhouses A and B. Overall, 16 isolates of Listeria spp.…”

“…The samples from pig tonsils in slaughterhouse B were taken in October 2019 (sampling dates 5 and 6); no environmental samples were taken due to organizational reasons. Sample transportation and examination, as well as confirmation of presumptive isolates, were performed as described by Oswaldi et al [ 18 ]. All confirmed isolates were stored under cryopreservation conditions at −80 °C in cryovials (ROTI ® Store cryovials, Carl Roth GmbH + Co. KG, Karlsruhe, Germany).…”

“…The prevalence of Listeria spp. in pigs in German slaughterhouses was described by Oswaldi et al [ 18 ]. L. monocytogenes is frequently found in pork products worldwide [ 19 , 20 ], especially in products intended to be eaten raw (ready-to-eat products); this poses a threat to public health [ 21 ].…”

Drinking Pipes and Nipple Drinkers in Pig Abattoir Lairage Pens—A Source of Zoonotic Pathogens as a Hazard to Meat Safety

“…Studies show that Listeria spp. occur on pig farms, in abattoirs and in the food processing industry being isolated from the skin or faeces of pigs [31][32][33]. Therefore, infected pigs can transfer Listeria spp.…”