Institute of Bacterial Infections and Zoonoses (IBIZ)

Listeriosis is a significant zoonotic bacterial disease affecting humans and various animal species worldwide. It is caused by Listeria monocytogenes and Listeria ivanovii, both of which are pathogenic to animals and humans and share common virulence factors. Listeria monocytogenes is a Gram-positive, non-spore-forming, motile, facultative anaerobic, intracellular rod-shaped bacterium. This highly virulent foodborne pathogen is commonly found in soil, silage, and other environmental sources, and can survive freezing, drying, and heat. In humans, infection is primarily linked to consumption of contaminated raw foods, including raw meat, milk, cheeses, ice cream, raw vegetables, and smoked fish. Clinical manifestations in humans include sepsis, fever, foodborne illness, encephalitis, and intrauterine or cervical infections in pregnant women, which may lead to spontaneous abortion.

Listeriosis in animals is mainly sporadic and associated with the consumption of spoiled feed. Main clinical signs include septicemia, abortion or latent infection, and gastrointestinal complications. In ruminants, the most common form affects the central nervous system, causing encephalitis or meningoencephalitis, results in a condition known as "circling disease." Listeriosis in animals is a nationwide concern in Germany, with annual incidence rates rising. The disease primarily affects food-producing animals such as cattle, sheep, and goats, resulting in economic losses and public health risks. Listeriosis also impacts wildlife, including foxes, raccoons, fallow deer, roe deer, wild rabbits, wild pigs, and poultry such as chickens, pigeons, and waterfowl.

Listeria isolates are traditionally classified by antigen-based serotyping, which uses somatic O and flagellar H antigens to distinguish four serogroups (1/2, 3, 4, 7) and 14 serovars (1/2a, 1/2b, 1/2c, 3a, 3b, 3c, 4a, 4b, 4ab,4c, 4d, 4e, 4h and 7). Of these, serotypes 1/2a, 1/2b, and 4b account for 95% of human illness cases, with serotype 4b most often linked to outbreaks. In addition to antigen-based methods, however, Listeria isolates are also classified molecularly into five genotypes (IIa, IIb, IIc, IVa, and IVb).

In our laboratory, Listeria detection is performed by culturing the pathogen from animal samples and subsequently testing antibiotic susceptibility to identify the effective antibiotics, as well as molecular characterization of the genogroups using multiplex PCR and WGS.

The main tasks of the animal listeriosis laboratory are to support state laboratories by conducting confirmatory tests and providing regular interlaboratory comparison tests.

• Development and validation of diagnostic methods for animal listeriosis.
• Participate in action plans, develop recommendations and advice, and prepare expert opinions to enhance preparedness for animal listeriosis risks.
• Conduct prevalence and resistance studies on Listeria monocytogenes.
• Develop techniques for phenotypic and molecular characterization of Listeria monocytogenes.
• Listeriae strain collection from different animal species, production of reference material, and conduct of interlaboratory tests.
• Promote awareness and strengthen competence regarding animal listeriosis.
• Annual reporting and publication of work findings

• Our research focuses on the molecular characterization of Listeriamonocytogenes of animal origin, aiming to determine genogroup and thereby emphasizing our dedication to understanding pathogen diversity and resistance development.
• Antimicrobial susceptibility testing (AST) and identification of resistance genes in animal isolates help elucidate how resistance develops in animal-derived isolates.
• Genomic surveillance employing Next-Generation Sequencing (NGS) examines host and pathogen factors related to virulence mechanisms and infection in Listeria monocytogenes. 

• Isolation and bacteriological identification
• Utilization of molecular techniques for genogrouping.
• Antibiotic resistance testing through both traditional and emerging methods.
• Application of next-generation sequencing

• Wareth G, Neubauer H. The striking incidence of animal listeriosis in Germany (2014-2024) indicates a persis-tent but neglected risk for One Health. Vet Res. 2025 Mar 8;56(1):53. https://doi/10.1186/s13567-025-01481-4.
• Ruppitsch W, Pietzka A, Prior K, Bletz S, Fernandez HL, Allerberger F, et al. Defining and evaluating a core genome multilocus sequence typing scheme for whole-genome sequence-based typing of Listeria monocytogenes. J Clin Microbiol. 2015;53(9):2869–76. doi.org/10.1128/JCM.01193-15.
• Doumith M, Buchrieser C, Glaser P et al. (2004): Differentiation of the major Listeria mono-cytogenes serovars by multiplex PCR. J Clin Microbiol 42 (8), 3819-3822. doi/10.1128/JCM.42.8.3819-3822.2004.   
• Verordnung (EU) 2024/2895 der Kommission vom 20. November 2024 zur Änderung der Verordnung (EG) Nr. 2073/2005 hinsichtlich Listeria monocytogenes.
• Tiergesundheitsgesetz – TierGesG