Particularities of laboratory diagnostics of Listeria spp

Abstract

Cite this article: Borovik, I. V., & Zazharska, N. M. (2019). Particularities of laboratory diagnostics of Listeria spp. Theoretical and Applied Veterinary Medicine, 7(4), 236‒244. doi: 10.32819/2019.74041 Abstract. The laboratory diagnosis of Listeria spp is imperfect, and the detection of Listeria spp pathogen from the products is complicated by the presence of other microflora. Detection of Listeria spp under laboratory conditions has been improved. The causative agent Listeria spp was isolated from food (meat and meat products, sour milk and hard cheese, fish), washes from environmental objects, pathological material (poultry corpses). The morphological properties of different reference strains of Listeria spp (L. monocytogenes, L. ivanovii, L. seeligeri, L. grayi, L. welshimeri, L. innocua, L. murray) were compared. It is noted that all species have a rod-shaped and coccygeal form of microorganism. In smears it is quite rare to find a pathogen in the form of a «V» shape. Nutrient selective media from different manufacturers (Graso Biotech, Merck, Biolife Italiana, BioMerieux, HiMedia, Lab M, Difco) were used to study the growth properties and identification of the pathogen. The best results are obtained with medium from Graso Biotech and Merck. The method of primary and secondary accumulation was improved to guarantee the increase in the concentration of the Listeria pathogen: increasing the weight of the sample and reducing the volume of the solvent, reducing the amount of Freser broth and increasing the volume of the original suspension. Improvements in the scheme of CAMP-test prevent the merger of the hemolysis zone of the studied cultures. It is recommended to combine СAMP-test with a hemolytic test (puncture method), which allows to observe mirror hemolysis. The reference strains of Staphylococcus aureus and Rhodococcus equi are classically used for the CAMP-test, but Listeria exhibits hemolytic properties with other types of microorganisms. According to our practical experience also β-hemolytic cultures: Bacillus subtilis, Streptococcus pyogenes, Streptococcus agalactiae or Clostridium perfringens. Cultures that do not have hemolytic properties – Escherichia сolі, Enterococcus faecalis. The determination of hemolytic properties of Listeria is offered by strains of microorganisms – Bacillus subtilis and Escherichia сolі. For the identification of the pathogen, the method of enzyme-linked immunosorbent fluorescence analysis on an automatic Vidas analyzer was used. This method shortens the study period to one day in case of a negative result as opposed to the classical one (5 days). We suggest using the Vidas Listeria Duo test system to identify L. monocytogenes and Listeria spp. Using the Listeria10300 API test system allows one to determine the biochemical properties of the pathogen in one day. According to the results of bioassay in mice pathogenic properties have both L. monocytogenes and L. ivanovii.