Serotype identification and antibiotic resistance analysis of Listeria monocytogenes isolates recovered from animal products in 2021–2024

Introduction. Listeria monocytogenes is a pathogenic microorganism that causes a large number of deaths due to the consumption of contaminated animal products. This underpins the relevance of monitoring the spread of the listeriosis agent in raw materials, animal products, and environmental objects, as well as the antibiotic resistance of isolates. Objective. Serotype identification and antibiotic resistance analysis of Listeria monocytogenes isolates recovered from animal products in 2021–2024. Materials and methods. The work was performed at the Microbiology Unit of the Vladimir Testing Laboratory, the Federal Centre for Animal Health. Listeria genus bacteria isolates were identified using time-of-flight mass spectrometry. Antibiotic resistance of isolates belonging to the species Listeria monocytogenes was determined by the disk diffusion method. The values of the growth retardation zones were interpreted according to the Russian recommendations “Determination of the sensitivity of microorganisms to antimicrobial drugs” (IACMAC, version 2025-01). Listeria serological groups were identified using real-time polymerase chain reaction (qPCR) with primers manufactured by Syntol (Russia). Results. The article presents the results of antibiotic resistance testing of 77 Listeria monocytogenes isolates detected in animal products in 2021–2024, as well as their differentiation by serogroups. Listeria monocytogenes was most frequently detected in poultry products. The detected isolates showed maximum resistance to cefuroxime, sulfamethoxazole/trimethoprim, norfloxacin, rifampicin, levofloxacin, and kanamycin. Moreover, most isolates exhibited resistance to more than one antimicrobial medicinal product. The study established the belonging of the Listeria monocytogenes isolates to the following serogroups: IIa (serotypes 1/2a, 3a) – 92.2%; IIc (serotypes 1/2c, 3c) – 5.2%; IVb (serotypes 4b, 4d, 4e) – 2.6%. Conclusion. The spread of resistance, including multidrug resistance, among Listeria monocytogenes isolates detected in animal products in 2021–2024 was demonstrated. The study identified the presence of listeria belonging to group IVb (serotypes 4b, 4d, 4e). However, the dominant part of Listeria monocytogenes isolates was classified as group IIa (serotypes 1/2a, 3a).