Genotyping of Listeria by Polymerase Chain Reaction (PCR) and its Epidemiological Significance

The purpose of the study. The article covers the issues of genotyping of listeria by polymerase chain reaction (PCR) and its epidemiological significance. It is known that molecular genetic methods allow to detect specific microbial pathogens, virulence markers, antimicrobial resistance genes faster and with greater sensitivity than traditional culture methods. Therefore, the development of detection methods and genotyping by polymerase chain reaction (PCR) is relevant. Materials and methods. For the detection and genotyping of Listeria, the technology of DNA chips is becoming increasingly important, which can significantly expand the possibilities of molecular detection. Chip technology can be used to simultaneously identify a whole range of pathogenic microorganisms, to determine genetic virulence markers, the relationship to antibiotics, subtyping, as well as to determine the quality of microorganisms in samples. A simplified version of DNA chip technology is multiplex (numerical) PCR, which is used to detect and genotype listeria. Studies have shown that to detect Listeria spp. using a polymerase chain reaction, it is advisable to use the gene iap (invasive associated protein), known for 6 species of listeria, which encodes a protein P 60 that is common to all species of listeria, including L.murrayi. Computer analysis revealed areas with 100% homology, from which primers were selected for PCR detection of all types of listeria. Areas of genomes characterized by 100% homology were selected for further analysis and labeling of primer sets. The sequences of the constructed primers List 1 and List 2 allowed to identify 6 species of Listeria (L. monocytogenes, L. innocua, L. ivanovii, L. grayi, L. seeligeri, L. welshimeri). Increasing the length of the primer leads to the increasing of specificity of PCR analysis. The greater the length of the primer, the smaller the specific gravity of one error of the unpaired nucleotide. The degree of primer homology is a key parameter that indicates the "quality" of a set of primers. Results and discussion. It is established that a significant disadvantage of the vast majority diagnosed using PCR test systems is the lack of internal control of amplification. The negative result of PCR analysis may be due to the absence in the clinical material of a fragment of the Listeria genome, and the fact that the PCR product was not synthesized for other reasons. They may be as the following ones: operator errors, erroneously determined reaction mixture concentrations and PCR temperature parameters. False-negative results can also be caused by factors that inhibit thermostable DNA polymerase. In its turn, such inhibition of the enzyme responsible for amplification is caused by a very large amount of DNA - template, pre-treatment of clinical samples. It has been shown that 80% of clinical specimens contain a substance that inhibits DNA polymerase. Therefore, it is necessary to use internal control, the positive result of the reaction of which indicates the successful amplification, that is the absence of false positive results. Conclusion. There are several reasons why the accuracy of PCR analysis does not reach 100%. Accuracy depends on the technology (variety) of PCR - the method used (ordinary or fluorescent), detection of amplicons, PCR homogeneous or nested, nested in one test tube or in two test tubes, as well as the level of quality of the survey (primarily on the technical parameters of the amplifier). The test systems used can be used for PCR detection and are recommended as standard primer sets for the detection and cross-species testing of listeria, which is important for the timely implementation of appropriate anti-epidemic measures in listeriosis